ALBERT

Description: A numerical method for detection of unstable periodic orbits on attractors of nonlinear models is proposed.  The method requires similar techniques to data assimilation.  This fact facilitates its implementation for geophysical models.  This method was used to find numerically several low-period orbits for the barotropic ocean model in a square.  Some numerical particularities of application of this method are discussed. Knowledge of periodic orbits of the model helps to explain some of these features like bimodality of probability density functions (PDF) of principal parameters.  These PDFs have been reconstructed as weighted averages of periodic orbits with weights proportional to the period of the orbit and inversely proportional to the sum of positive Lyapunov exponents. The fraction of time spent in the vicinity of each periodic orbit has been compared with its instability characteristics. The relationship between these values shows the 93% correlation.  The attractor dimension of the model has also been approximated as a weighted average of local attractor dimensions in vicinities of periodic orbits.

Description: Based on quasilinear theory, a closure scheme for anisotropic multi-component fluid equations is developed for the wave-particle interactions of ions with electromagnetic Alfvén and ion-cyclotron waves propagating along the mean magnetic field. Acceleration and heating rates are calculated. They may be used in the multi-fluid momentum and energy equations as anomalous transport terms. The corresponding evolution equation for the average wave spectrum is established, and the effective growth/damping rate for the spectrum is calculated. Given a simple power-law spectrum, an anomalous collision frequency can be derived which depends on the slope and average intensity of the spectrum, and on the gyrofrequency and the differential motion (with respect to the wave frame) of the actual ion species considered. The wave-particle interaction terms attain simple forms resembling the ones for collisional friction and temperature anisotropy relaxation (due to pitch angle scattering) with collision rates that are proportional to the gyrofrequency but diminished substantially by the relative wave energy or the fluctuation level with respect the background field. In addition, a set of quasilinear diffusion equations is derived for the reduced (with respect to the perpendicular velocity component) velocity distribution functions (VDFs), as they occur in the wave dispersion equation and the related dielectric function for parallel propagation. These reduced VDFs allow one to describe adequately the most prominent observed features, such as an ion beam and temperature anisotropy, in association with the resonant interactions of the particles with the waves on a kinetic level, yet have the advantage of being only dependent upon the parallel velocity component.

Description: Ocean surface, grazing-angle radar backscatter data from two separate experiments, one of which provided coincident time series of measured surface winds, were found to exhibit signatures of deterministic chaos. Evidence is presented that the lowest dimensional underlying dynamical system responsible for the radar backscatter chaos is that which governs the surface wind turbulence. Block-averaging time was found to be an important parameter for determining the degree of determinism in the data as measured by the correlation dimension, and by the performance of an artificial neural network in retrieving wind and stress from the radar returns, and in radar detection of an ocean internal wave. The correlation dimensions are lowered and the performance of the deterministic retrieval and detection algorithms are improved by averaging out the higher dimensional surface wave variability in the radar returns.

Description: Application of the Brown-Samelson theorem, which shows that particle motion is integrable in a class of vorticity-conserving, two-dimensional incompressible flows, is extended here to a class of explicit time dependent dynamically balanced flows in multilayered systems. Particle motion for nonsteady two-dimensional flows with discontinuities in the vorticity or potential vorticity fields (modon solutions) is shown to be integrable. An example of a two-layer modon solution constrained by observations of a Gulf Stream ring system is discussed.

Description: A nonlinear nested model for mudslide-induced tsunamis is proposed in which three phases of the life of the wave, i.e. the generation, far-field propagation and costal run-up are described by means of different mathematical models, that are coupled through appropriate matching procedures. The generation and run-up dynamics are simulated through a nonlinear shallow-water model with movable lateral boundaries: in the generation region two active layers are present, the lower one describing the slide descending on a sloping topography. For the intermediate phase, representing wave propagation far from the generation region, the hydrostatic assumption is not assumed as appropriate in general and, therefore, a nonlinear model allowing for weak phase dispersion, namely a Kadomtsev-Petviashvili equation, is used. This choice is made in order to assess the relevance of dispersive features such as solitary waves and dispersive tails. It is shown that in some realistic circumstances dispersive mudslide-induced tsunami waves can be produced over relatively short, distances. In such cases the use of a hydrostatic model throughout the whole tsunami history turns out to give erroneous results. In particular, when solitary waves are generated during the tsunami propagation in the open sea, the resulting run-up process yields peculiar wave forms leading to amplified coastal inundations with respect to a mere hydrostatic context.

Description: The theory of scale similarity and breakdown coefficients is applied here to intermittent rainfall data consisting of time series and spatial rain fields. The probability distributions (pdf) of the logarithm of the breakdown coefficients are the principal descriptor used. Rain fields are distinguished as being either multiscaling or multiaffine depending on whether the pdfs of breakdown coefficients are scale similar or scale dependent, respectively. Parameter  estimation techniques are developed which are applicable to both multiscaling and multiaffine fields. The scale parameter (width), σ, of the pdfs of the log-breakdown coefficients is a measure of the intermittency of a field. For multiaffine fields, this scale parameter is found to increase with scale in a power-law fashion consistent with a bounded-cascade picture of rainfall modelling. The resulting power-law exponent, H, is indicative of the smoothness of the field. Some details of breakdown coefficient analysis are addressed and a theoretical link between this analysis and moment scaling analysis is also presented. Breakdown coefficient properties of cascades are also investigated in the context of parameter estimation for modelling purposes.

Description: By using a Hamiltonian method, non-linear three-wave interaction in a class of systems related to the shallow water model is considered and a general coupling coefficient is presented. In the special case where two inertial waves and one Rossby wave interact resonantly, it is found that even a very small shear of the background velocity can be important in the interaction process. The stability of the system is considered by using a pseudo-energy method. Some implications for the dynamics of atmospheric flows are pointed out.

Description: The paper concerns the temporal evolution of the Rayleigh-Taylor instability of two superimposed fluids in a vertical channel. At large times the instability results in the formation of a wide nearly-steady bubble of the lighter fluid rising through the channel, and thin long unsteady jets of the heavier fluid flowing down the channel walls. The jet flow appears to be tractable asymptotically by the method of matched expansions. The solution has been obtained with the planar tips of jets characterized by the jump of the interface slope.

Description: When a pollutant is released into the ocean or atmosphere under turbulent conditions, even a steady release is captured by large eddies resulting in localized patches of high concentration of the pollutant. If such a cloud of pollutant subsequently enters a stable stratification-either a pycnocline or thermocline-then internal waves are excited. Since large solitary internal waves have a recirculating core, pollutants may be trapped in the sclitary wave, and advected large distances through the waveguide provided by the stratification. This paper addresses the mechanisms, through computer and physical simulation, by which a localized release of a dense pollutant results in solitary waves that trap the pollutant or disperse the pollutant faster than in the absence of the waves.

Description: It is a common procedure in climate modelling to specify dynamical system components from an external source; a prominent example is the forcing of an atmospheric model with observed sea surface temperatures. In this paper, we examine the dynamics of such forced models using a simple prototype climate system. A particular fully coupled run of the model is designated the "true" solution, and an ensemble of perturbed initial states is generated by adding small errors to the "true" initial state. The perturbed ensemble is then integrated for the same period as the true solution, using both the fully-coupled model and a model in which the ocean is prescribed exactly from the true solution at every time step. Although the prescribed forcing is error-free, the forced-atmosphere ensemble is shown to converge to spurious solutions. Statistical tests show that neither the time-mean state nor the variability of the forced ensemble is consistent with the fully-coupled system. A stability analysis reveals the source of the inconsistency, and suggests that such behaviour may be a more general feature of models with prescribed subsystems. Possible implications for model validation and predictability are discussed.

Description: A one-dimensional form of the equation of motion with forcing and dissipation is formulated in the spectral domain and used to make long term integrations from which the spectral distribution of the kinetic energy is determined The forcing in the wave number domain is determined in advance and kept constant for the duration of the time integrations. The dissipation is proportional to the second derivative of the velocity. The applied equation is made non-dimensional by selecting a length scale from which the time scale and the velocity scale may be determined. The resulting equation contains no parameters apart from the forcing. The integrations use a large number of spectral components and no approximation is made with respect to the non-linear interaction among the spectral components. Starting from an initial state in which all the velocity components are set to zero the equation is integrated for a long time to see if it reaches a steady state. The spectral distribution of the kinetic energy is determined in the steady state, and it is found that the distribution, in agreement with observational studies, may be approximated by a power law of the form n-3 within certain wave number regions. The wave numbers for which the -3 power law applies is found between the region of maximum forcing and the dissipation range. The intensity of the maximum forcing is varied to see how the resulting steady state varies. In addition, the maximum number of spectral components is varied. However, the available computing power sets an upper limit to the number of components.

Description: The nonlinear dustgrain-charging and the influence of the ion density and temperature on electrostatic waves in a dusty plasma having trapped ions are investigated by numerical calculation. This work is the first approach to the effect of trapped ions in dusty plasmas. The nonlinear variation of the dust-charge is examined, and it is shown that the characteristics of the dustcharge number sensitively depend on the plasma potential, Mach number, dust mass-to-charge ratio, trapped ion density and temperature. The fast and slow wave modes are shown in this system. An increase of the ion temperature decreases the dust-charging rate and the propagation speed of ion waves. It is found that the existence of electrostatic ion waves sensitively depends on the ion to electron density ratio. New findings of the variable-charge dust grain particles, ion density and temperature in a dusty plasma with trapped ions are predicted.

Description: In this paper we investigate whether observed intraseasonal variability in the equatorial Pacific can be attributed to finite amplitude waves resulting from unstable air-sea interactions. Within a Zebiak - Cane type model of the coupled equatorial ocean - atmosphere, the nonlinear equilibration of instabilities of a simple basic state is considered with periodic conditions on the ocean boundaries. Three mechanisms exist which can induce a finite amplitude equilibration on a time scale ε2t. Here t is the characteristic time scale of growth of the disturbance and ε the relative distance from the instability threshold. For each equilibration mechanism, the finite amplitude and period of the equilibrium state are computed as a function of ε and substantial amplitude can be reached for a reasonable degree of supercriticality. Thereafter the analysis is extended to include time-dependent external forcing. It is shown that interannual variability may result through the interaction of the response of a weak annual external forcing and the finite amplitude development of the intraseasonal instabilities.

Description: A one-dimensional Burridge-Knopoff spring-block model with slip-dependent friction was studied to explore the possibility of a solitary wave solution existing for the problem of earthquake faulting. The result may be used as an alternative case of the crack model (e.g., Madariaga and Cochard, 1996) and the spring-block model with velocity-dependent friction (e.g., Carlson and Langer, 1989) in the understanding of the mechanism of the self-healing slip pulse proposed by Heaton (1990). In general, the conditions for a solitary wave solution to exist are discussed by the trajectory in the phase space. By taking the first order approximation, it is demonstrated that a solitary wave solution exists in which the slip behaves as a propagating solitary wave with the propagation velocity less than that of an acoustic (seismic) wave, and the source time function at each position remains the same. As an alternative approach other than numerical calculations, the analytical solution, although simple, sheds light on some of the properties of the self-healing slip pulse. From the solution it is seen that the width of the pulse depends on its propagation velocity and the friction, consistent with experience in physics. It is pointed out that the self-healing slip pulse may exist for a broad class of frictional constitutive laws which, to some extent, explains the fact that the self-healing slip pulse may be observed for a variety of earthquakes occurring within different seismogenic environments.

Description: We consider solitary waves propagating on the interface between two fluids, each of constant density, for the case when the upper fluid is bounded above by a rigid horizontal plane, but the lower fluid has a variable depth. It is well-known that in this situation, the solitary waves can be described by a variable-coefficient Korteweg-de Vries equation. Here we reconsider the derivation of this equation and present a formulation which preserves the Hamiltonian structure of the underlying system. The result is a new variable-coefficient Korteweg-de Vries equation, which conserves energy to a higher order than the more conventional well-known equation. The new equation is used to describe the transformation of an interfacial solitary wave which propagates into a region of decreasing depth.

Description: The run-up of solitary-type pulses propagating at a small angle with respect to the shore normal is analysed by means of a weakly-two-dimensional extension of a solution of the nonlinear shallow water equations for a non-breaking, solitary pulse incident and reflecting on an inclined plane beach similar to that of Synolakis (1987). A simple analytic expression for the longshore velocity of the solitarytype pulse is given along with examples of computations. The proposed solution can be employed in modelling run-up flow properties of solitary-type pulses (e.g. tsunamis, primary waves of wave groups propagating in shallow waters, ...). The hodograph transformation that is used and the flow properties are illustrated in terms of contour plots. A limiting pulse amplitude is defined such that breakdown of the solution occurs. A solution for the run-up of multiplesolitary-pulses in shallow waters is also described. Some of the salient characteristics are illustrated and discussed. Breakdown conditions are analytically defined also for the multiple-solitary-pulses solution. A strong condition is given which couples information on both pulses amplitudes and distances. An easier (but weaker) version of the criterion is given in terms of a pair of decoupled formulae one for the Pulses amplitudes and the second for their initial positions. Very large run-up is achieved because of the merging of two or more solitary pulses which are smaller than the limiting Pulse. The role of pulse separation within a group of solitary Pulses is also analysed in terms of both a 'nonlinearity parameter' N and a 'groupiness parameter' G. It is found that a critical distance exists between two pulses which minimizes the back-wash velocity and, as a consequence, the nonlinearity parameter N.

Description: The dynamics of weakly nonlinear wave trains in unstable media is studied. This dynamics is investigated in the framework of a broad class of dynamical systems having a Hamiltonian structure. Two different types of instability are considered. The first one is the instability in a weakly supercritical media. The simplest example of instability of this type is the Kelvin-Helmholtz instability. The second one is the instability due to a weak linear coupling of modes of different nature. The simplest example of a geophysical system where the instability of this and only of this type takes place is the three-layer model of a stratified shear flow with a continuous velocity profile. For both types of instability we obtain nonlinear evolution equations describing the dynamics of wave trains having an unstable spectral interval of wavenumbers. The transformation to appropriate canonical variables turns out to be different for each case, and equations we obtained are different for the two types of instability we considered. Also obtained are evolution equations governing the dynamics of wave trains in weakly subcritical media and in media where modes are coupled in a stable way. Presented results do not depend on a specific physical nature of a medium and refer to a broad class of dynamical systems having the Hamiltonian structure of a special form.

Description: A new model for simulating non-negative random processes is developed. The model is based on a bounded random multiplicative cascade with a lognormal generator with the scale parameter dependent on the number of steps in the cascade. It is shown, both analytically and numerically, that the simulated field has multiaffine properties within some restricted range of scales. This type of random processes is defined here as quasi-multiaffine. A procedure for retrieving the modelling parameters from real data is also discussed.

Description: TOPEX/POSEIDON (T/P) sea level deviation (SLD) time series from 3 October 1992 to 15 May 1997 combined with upper ocean thermal structures are used to observe the characteristics and analyze the dynamics of equatorial waves in the Pacific Ocean. The evolution of the Kelvin wave propagating along an eastward shoaling thermocline in the equatorial Pacific is investigated. The behaviour of this wave as it propagates eastward can be approximately described with the solutions of the perturbed Korteweg-de Vries (PKDV) equation and modified Green's Law. Assuming that the nonlinear term and dispersive term of this equation are balanced, the amplitude increases as the thermocline decreases to the power -3/8. Approaching the eastern Pacific, the nonlinearity increases and the relation changes to the power -9/8. The dispersion relation, and mass and energy conservations are investigated. The results indicate that under a varying thermocline, the nonlinear Kelvin solitary waves indeed exist in the real ocean.

Description: Hide (Nonlinear Processes in Geophysics, 1998) has produced a new mathematical model of a self-exciting homopolar dynamo driving a series- wound motor, as a continuing contribution to the theory of the geomagnetic field. By a process of exact perturbation analysis, followed by combination and partial solution of differential equations, the complete nonlinear quenching of current fluctuations reported by Hide in the case that a parameter ε has the value 1 is proved via the Popov theorem from feedback system stability theory.

Description: We consider particle motion in nonautonomous 1 degree of freedom Hamiltonian systems for which H(p,q,t) depends on N periodic functions of t with incommensurable frequencies. It is shown that in near-integrable systems of this type, phase space is partitioned into nonintersecting regular and chaotic regions. In this respect there is no different between the N = 1 (periodic time dependence) and the N = 2, 3, ... (quasi-periodic time dependence) problems. An important consequence of this phase space structure is that the mechanism that leads to fractal properties of chaotic trajectories in systems with N = 1 also applies to the larger class of problems treated here. Implications of the results presented to studies of ray dynamics in two-dimensional incompressible fluid flows are discussed.

Description: The behaviour of the error growth is analyzed in several simple examples of systems with external time-dependent forcings. in some systems oscillations of the error around the saturation level can be observed. A common feature of these examples is the error growth dependence on initial time. In the examples here considered the improvement in the predictability derived from an adequate choice of the Initial time is comparable to those obtained by reducing the initial errors.

Description: The rupture on a fault resulting in an earthquake is clearly a complex process. In order to better understand this process the continuum version of the slider-block model has been considered in some detail. In particular, the role of a cohesive breakaway zone is considered. Solutions of a "piston" problem and a "shock-tube" problem are obtained. For the "dirven" problem the cohesive breakaway solution is combined with a viscous resistance on the fault to obtain solutions that are reasonably realistic in terms of fault rupture.

Description: This paper presents developments of the Harniltonian Approach to problems of fluid dynamics, and also considers some specific applications of the general method to hydrodynamical models. Nonlinear gauge transformations are found to result in a reduction to a minimum number of degrees of freedom, i.e. the number of pairs of canonically conjugated variables used in a given hydrodynamical system. It is shown that any conservative hydrodynamic model with additional fields which are in involution may be always reduced to the canonical Hamiltonian system with three degrees of freedom only. These gauge transformations are associated with the law of helicity conservation. Constraints imposed on the corresponding Clebsch representation are determined for some particular cases, such as, for example. when fluid motions develop in the absence of helicity. For a long time the process of the introduction of canonical variables into hydrodynamics has remained more of an intuitive foresight than a logical finding. The special attention is allocated to the problem of the elaboration of the corresponding regular procedure. The Harniltonian Approach is applied to geophysical models including incompressible (3D and 2D) fluid motion models in curvilinear and lagrangian coordinates. The problems of the canonical description of the Rossby waves on a rotating sphere and of the evolution of a system consisting of N singular vortices are investigated.

Description: A general coupling coefficient for three wave interactions in an ideal MHD plasma is presented. Using a special stratified background atmosphere, an explicit symmetric form of the coupling coefficient is derived.

Description: Soil moisture gradients along hillslopes in humid watersheds, although indicated by vegetation gradients and by studies using models, have been difficult to confirm empirically. While soil properties and topographic features are the two general physio-graphic factors controlling soil moisture on hillslopes, studies have shown conflicting results regarding which factor is more important. The relative importance of topographic and soil property controls was examined in an upland forested watershed at the Coweeta Hydrologic Laboratory in the southern Appalachian mountains. Soil moisture was measured along a hillslope transect with a mesic-to-xeric forest vegetation gradient over a period spanning precipitation extremes. The hillslope was transect instrumented with a time domain reflectometry (TDR) network at two depths. Soil moisture was measured during a severe autumn drought and subsequent winter precipitation recharge. In the upper soil depth (0-30 cm), moisture gradients persisted throughout the measurement period, and topography exerted dominant control. For the entire root zone (0-90 cm), soil moisture gradients were found only during drought. Control on soil moisture was due to both topography and storage before drought. During and after recharge, variations in soil texture and horizon distribution exerted dominant control on soil moisture content in the root zone (0-90 cm). These results indicate that topographic factors assert more control over hillslope soil moisture during drier periods as drainage progresses, while variations in soil water storage properties are more important during wetter periods. Hillslope soil moisture gradients in southern Appalachian watersheds appear to be restricted to upper soil layers, with deeper hillslope soil moisture gradients occurring only with sufficient drought.

Description: Dambos, seasonally saturated wetlands, are widespread in headwater catchments in southern Africa and play an important role in the regional hydrological cycle. However, the processes influencing runoff from these catchments are poorly understood. This paper reports an isotopic investigation of runoff-generating mechanisms within a Zimbabwean catchment containing a dambo. Hydrograph separation using deuterium reveals that, once the dambo is saturated, up to 70% of total storm flow can be considered "new" water (i.e. derived directly from rainfall generating the runoff event). However, both the total proportion and the instantaneous maximum amount of "new" water in hydrographs are sensitive to rainfall characteristics and antecedent conditions. These results are (1) compatible with observations made in catchments in temperate climates when wetlands are present, and contrast with results obtained when wetlands are absent and (2) consistent with saturation overland flow, generated in saturated regions of the dambo, being the major storm runoff mechanism. To reconcile these observations with past perceptions that dambos attenuate flood flows, a dual role for dambos in storm flow production is postulated.

Description: The use of the nonparametric nearest-neighbour resampling technique is studied for generating time series of daily rainfall and temperature for seven stations in the German part of the Rhine basin. The emphasis is on the reproduction of extreme N-day precipitation amounts. The daily temperatures are used to determine snow accumulation and melt in winter. Two versions of the resampling method, conditional on the atmospheric circulation and unconditional, show comparable results. For precipitation, the autocorrelation properties are well reproduced, whereas for temperature the autocorrelation coefficients are systematically underpredicted. The distributions of the N-day annual maximum precipitation amounts are adequately preserved. Despite the systematic underprediction of the temperature autocorrelation, the distributions of N-day maximum snowmelt are well reproduced. A 1000-year simulation for the seven stations shows that unprecedented rainfall situations can be generated.

Description: By using topographic indices as derived from a Digital Terrain Models (DTM), it is possible to represent the heterogeneity within a landscape. This heterogeneity can reflect both long term evolutionary patterns seen in a landscape and the short term forcing of flow dynamics during storm events. By spatial analysis, the linkage between the geomorphological- hydrological-plant physiological phenomena can be examined. In this study, a direct link will be established between the topographically-driven hydrological phenomena and the eco-physiological response. The topographic distribution function of TOPMODEL is used to control the spatial and temporal flux of the channel flow and water table. The plant physiological model GAS-FLUX is used to give a spatially and temporally dissaggregated species-sensitive estimate of evapotranspiration flux. Evapotranspiration is sensitive to the vegetation phonology, to tundra community physiology and to the temperature regime. A simple linking of TOPMODEL and the GAS-FLUX model is applied to a summer snow-free period to the Imnavait catchment, Alaska (2.2 km2). A species-sensitive evapotranspiration model proved to give the highest quality results when validated against flow observations. Predicted dynamics of variable source area and the component hydrological processes are illustrated.

Description: A modification to the well-known water quality model "Quality Simulation Along River Systems" (QUASAR) is presented, extending its utility to real-time forecasting applications such as the management and control of pollution incidents. Two aggregated dead-zone (ADZ) parameters, namely time delay and dispersive fraction, are incorporated into the existing model formulation, extending the current continuously stirred tank reactor based model processes to account for advective and active mixing volume dispersive processes. The resulting river water quality model combines the strengths of the QUASAR model, which has proven non-conservative pollutant modelling capabilities, with the accurate advection and dispersion characterisation of the ADZ model. A discrete-time mathematical representation of the governing equations is developed that enables efficient system identification methods of parameter estimation to be utilised. The enhanced water quality model and associated methods of parameter estimation are validated using data from tracer experiments conducted on the River Mimram. The revised model produces accurate predictions of observed concentration-time curves for conservative substances.

Description: A one-dimensional model is used to investigate the relationship between land subsidence and compaction of basin sediments in response to sediment loading. Analysis of the model equations and numerical experiments demonstrate quasi-linear systems behaviour and show that rates of land subsidence due to compaction: (i) can attain a significant fraction (〉40%) of the long-term sedimentation rate; (ii) are hydrodynamically delayed with respect to sediment loading. The delay is controlled by a compaction response time τc that can reach values of 10-5-107 yr for thick shale sequences. Both the behaviour of single sediment layers and multiple-layer systems are analysed. Subsequently the model is applied to the coastal area of the Netherlands to illustrate that lateral variability in compaction-derived land subsidence in sedimentary basins largely reflects the spatial variability in both sediment loading and compaction response time. Typical rates of compaction-derived subsidence predicted by the model are of the order of 0.1 mm/yr but may reach values in excess of 1 mm/yr under favourable conditions.

Description: A simple distributed rainfall-runoff model, configured on a square grid to make best use of weather radar data, was developed in Part 1 (Bell and Moore, 1998). The simple form of the basic model, referred to as the Simple Grid Model or SGM, allows a number of model variants to be introduced, including probability-distributed storage and topographic index representations of runoff production and formulations which use soil survey and land use data. These models are evaluated here on three catchments in the UK: the Rhondda in south Wales, the Wyre in north-west England and the Mole in the Thames Basin near London. Assessment is initially carried out in simulation mode to focus on the conversion of rainfall to runoff as influenced by (i) use of radar or raingauge input, (ii) choice of model variant, and (iii) use of a lumped or distributed model formulation. Weather radar data, in grid square and catchment average form, and raingauge data are used as alternative estimates of rainfall input to the model. Results show that when radar data are of good quality, significant model improvement may be obtained by replacing data from a single raingauge by 2 km grid square radar data. The performance of the Simple Grid Model with optimised isochrones is only marginally improved through the use of different model variants and is generally preferred on account of its simplicity. A more traditional lumped rainfall-runoff model, the Probability-Distributed Moisture model or PDM, is used as a benchmark against which to assess the performance of the distributed models. This proves hard to better, although the distributed formulation of the Grid model proves more reliable for some storm and catchment combinations where spatial effects on runoff response are evident. Assessment is then carried out in updating mode to emulate a real-time forecasting environment. First, a state updating form of the Grid Model is developed and then assessed against an ARMA error-prediction technique. Both state updating and error prediction give much improved model performance when compared with simulation mode results. No one updating technique is superior, with the simulation model formulation having greatest impact on forecast accuracy. However, when the results from the different catchments are considered together it is apparent that in the rapidly responding Rhondda catchment state updating gives slightly better results, while in the slower responding Wyre and Mole catchments, error prediction is slightly superior. This is attributed to the greater difficulty of reliably adjusting states when there are significant time delays associated with the catchment response. In general, the influence of rainfall input type, model variant and distributed versus lumped model reflect the results obtained in simulation mode. Updating doesn't fully compensate for a poor rainfall input or a deficient rainfall-runoff model formulation, especially for longer forecast lead times.

Description: The possibility of modelling the temporal structure of rainfall in southern Sweden by a simple cascade model is tested. The cascade model is based on exact conservation of rainfall volume and has a branching number of 2. The weights associated with one branching are 1 and 0 with probability P(1/0), 0 and 1 with P(0/1), and Wx/x, and 1 - Wx/x, 0 〈 Wx/x, 〈 1, with P(x/x), where Wx/x is associated with a theoretical probability distribution. Furthermore, the probabilities p are assumed to depend on two characteristics of the rainy time period (wet box) to be branched: rainfall volume and position in the rainfall sequence. In the first step, analyses of 2 years of 8-min data indicates that the model is applicable between approximately 1 hour and 1 week with approximately uniformly distributed Wx/x values. The probabilities P show a clear dependence on the box characteristics and a slight seasonal nonstationarity. In the second step, the model is used to disaggregate the time series from 17- to 1-hour resolution. The model-generated data reproduce well the ratio between rainy and nonrainy periods and the distribution of individual volumes. Event volumes, event durations, and dry period lengths are fairly well reproduced, but somewhat underestimated, as was the autocorrelation. From analyses of power spectrum and statistical moments the model preserves the scaling behaviour of the data. The results demonstrate the potential of scaling-based approaches in hydrological applications involving rainfall disaggregation.

Description: This paper compares direct measurements of evaporation with the values predicted for reference transpiration. The measurements of actual evaporation were made using an eddy correlation device on a grass field adjacent to the river Thames. Measurements of soil moisture and the driving meteorological variables were also made. The results showed that, during a period with minimal rainfall but no water stress, the cumulative values of reference transpiration compared very well with the cumulative measured evaporation and changes in soil moisture content. However, the values on specific days did not compare well. Following significant rainfall, the measured evaporation increased for a few days, probably due to evaporation of free water from the canopy or soil. Reference transpiration fell consistently below the measured evaporation once the soil moisture deficits exceeded 140 to 150 mm.

Description: A survey and resurvey of 77 headwater streams in Wales provides an opportunity for assessing changes in streamwater chemistry in the region. The Model of Acidification of Groundwater In Catchment (MAGIC) has been calibrated to the second of two surveys, taken in 1994-1995, using a Monte-Carlo methodology. The first survey, 1983-1984, provides a basis for model validation. The model simulates a significant decline of water quality across the region since industrialisation. Agreed reductions in sulphur (S) emissions in Europe in accordance with the Second S Protocol will result in a 49% reduction of S deposition across Wales from 1996 to 2010. In response to these reductions, the proportion of streams in the region with mean annual acid neutralising capacity (ANC) 〉 0 is predicted to increase from 81% in 1995 to 90% by 2030. The greatest recovery between 1984 and 1995 and into the future is at those streams with low ANC. In order to ensure that streams in the most heavily acidified areas of Wales recover to ANC zero by 2030, a reduction of S deposition of 80-85% will be required.

Description: Two methods for modelling regional responses of lake water quality to changes in acidic deposition in southernmost Norway were examined. Both methods are based upon the MAGIC model but differ in mode of regional application; one uses site-specific while the other uses Monte-Carlo methods for model calibration. The simulations of regional responses from both methods were compared with observed responses based on data from three lake surveys in southernmost Norway conducted in 1974, 1986 and 1995. The regional responses of the two modelling approaches were quite similar and agreed well with the observed regional distributions of lakewater chemistry variables. From 1974 to 1986 the observed data indicated that despite a decline of approximately 10% in sulphate (SO4) deposition, the mean acid neutralizing capacity (ANC) of lakes in southernmost Norway declined by approximately 6 μeq l-1. Both modelling approaches simulated no change or a very small decline in mean ANC for that period. From 1986 to 1995 the observed data indicated that, in response to an approximate 40% decline in SO4 deposition, the mean ANC of lakes in southernmost Norway increased by 11-16 μeq l-1. The modelling approaches simulated increases of 9-10 μeq l-1 in mean ANC for the same period. Both simulations and observations indicate that 〉 65% of lakes in southernmost Norway were acidic in 1974 and 1995. Both simulation methods predict that 〉65% of the lakes in southernmost Norway will have positive ANC values within 10 years of reductions of SO4 deposition to 20% of 1974 levels. Of the two regionalization methods the site-specific method appears preferable, because whereas the Monte-Carlo method gives results for a region as a whole, the site-specific method also reveals patterns within the region. The maintenance of a one-to-one correspondence between simulated and observed systems means that simulation results can be mapped for a geographically explicit presentation of model results. The ability to examine geographic patterns of response is becoming increasingly important in regional assessments.

Description: The results from an application of MAGIC (Model of Acidification of Groundwater In Catchments) to 733 Scottish catchments are presented. The availability of representative, good quality soil data is frequently limiting factor for biogeochemical modelling, particularly those involving modelling at various spatial scales. This study tests the sensitivity of MAGIC to soil input data derived from two different methodologies; the "nearest neighbour method" considers the closest representative soil profile to a catchment, and the "spatial weighting method" of all soil types identified in a catchment, based on a soil physico-chemical classification of Scotland. Soil data (soil depth, density, cation exchange capacity and base saturation) calculated using the "nearest neighbour method" and the "spatial weighting method" were highly variable, although the range of upper and lower limits were greater for soil data produced using the nearest neighbour method. In contrast to the predominantly organic soil data calculated by the nearest neighbour method, the spatially weighted soil parameters included a greater proportion of mineral soils. With regard to simulated surface water Acid Neutralising Capacity (ANC) for 1851, 1997 and 2050, MAGIC predictions were similar irrespective of the methodology used to determine soil input parameters. However, soil input data derived from both methods resulted in variable base saturation predictions. It is concluded that the "nearest neighbour" methodology is most appropriate if the objective is to determine the predicted response of the most acid- sensitive sites within a region in line with the approach used in Critical Laod mapping. On the other hand, "spatial weighting" integrates catchment soils and represents a more robust methodology by which to determine changes in median soil and water response in a regional context. The anticipated reductions in S emissions associated with the Second S Protocol are predicted to have a marginal beneficial effect on the recovery of soils and surface waters of Scotland.

Description: A two-layer application of the catchment-based soil and surface water acidification model, MAGIC, was applied to 21 sites in the UK Acid Waters Monitoring Network (AWAMN), and the results were compared with those from a one-layer application of the model. The two-layer model represented typical soil properties more accurately by segregating the organic and mineral horizons into two separate soil compartments. Reductions in sulphur (S) emissions associated with the Second S Protocol and different forestry (land use) scenarios were modelled, and their effects on soil acidification evaluated. Soil acidification was assessed in terms of base saturation and critical loads for the molar ratio of base cations (CA2+ + MG 2+ + K+) to aluminium (Al) in soil solution. The results of the two-layer application indicate that base saturation of the organic compartment was very responsive to changes in land use and deposition compared with the mineral soil. With the two- layer model, the organic soil compartment was particularly sensitive to acid deposition, which resulted in the critical load being predicted to be exceeded at eight sites in 1997 and two sites in 2010. These results indicate that further reductions in S deposition are necessary to raise the base cation (BC):Al ratio above the threshold which is harmful to tree roots. At forested sites BC:Al ratios were generally well below the threshold designated for soil critical loads in Europe and forecasts indicate that forest replanting can adversely affect the acid status of sensitive term objectives of protecting and sustaining soil and water quality. Policy formulation must seek to protect the most sensitive environmental receptor, in this case organic soils. It is clear, therefore, that simply securing protection of surface waters, via the critical loads approach, may not ensure adequate protection of low base status organic soils from the effects of acidification.

Description: The theory of the geomorphological unit hydrograph (GUH) is examined critically and it is shown that the inherent assumption that the operation of the drainage network may be modelled by a corresponding network of linear reservoirs so restricts the instantaneous unit hydrograph (IUH) shape that the effects of further restrictions, reflecting the constraints imposed by the geomorphological laws of the channel network, cannot easily be identified. Without such identification, the geomorphological unit hydrograph theory is untestable and must remain only a plausible hypothesis providing an indication of a two-parameter IUH whose shape and scale factors must still be related empirically to appropriate catchment characteristics.

Description: The Model of Acidification of Groundwater In Catchments (MAGIC) has been calibrated to 94 catchments in Wales, enabling the quantification of regional response to reduced emissions under the second sulphur protocol and incorporating the potential impact of future changes in afforestation. To calibrate the model the methodology utilises, for each site, the best available data derived from databases which are consistent across the whole region but which vary in spatial resolution. The calibrated model closely matches observed stream water chemistry across the region. The predicted future response is a reduction in acidity of surface waters in the region. The recovery is less marked at forested catchments, and some forested sites undergo a further decrease in acid neutralising capacity (ANC). The predictions from the multiple-site method are statistically consistent with those produced by an alternative regional modelling method which is based upon Monte-Carlo procedures. The multiple-site method, however, has the advantage of providing future predictions which are also spatially distributed across the region.

Description: Major, minor and trace element chemistry of runoff at stormflow and baseflow from 67 catchments (2 to 5 ha in area) has been determined to investigate the effects of clear felling and replanting of conifers on stream water quality across Wales. Samples, collected by local forestry workers (Forest Enterprise staff) on a campaign basis on up to eight occasions, were for 16 mature first rotation standing forest: the remainder represented areas completely clear felled from less than one to up to forty years previously. As the waters drain acidic and acid sensitive soils, acidic runoff is often encountered. However, higher pH values with associated positive alkalinities and base cation enrichments are observed due to the influence of weathering reactions within the bedrock. There is little systematic variation in water quality between baseflow and stormflow for each site indicating a complex and erratic contribution of waters from the soil and underlying parent material. 80% or more of the data points show hardly any changes with felling time, but there are a few outlier points with much higher concentrations that provide important information on the processes operative. The clearest outlier felling response is for nitrate at five of the more recently felled sites on brown earth, gley and podzolic soil types. ANC, the prime indicator of stream acidity, shows a diverse response from both high to low outlier values (〉+400 to -300 μEq/l). In parallel to nitrate, aluminium, potassium and barium concentrations are higher in waters sampled up to 4 years post felling, but the time series response is even less clear than that for nitrate. Cadmium, zinc and lead and lanthanides/actinides show large variations from site to site due to localized vein ore-mineralization in the underlying bedrock. The survey provides a strong indication that forest harvesting can have marked local effects on some chemical components of runoff for the first four years after felling but that this is confined to a small number of sites where nitrate production and aluminium leaching are high. In general, deforestation leads to a reversal of acidification when the nitrate pulse is low. The variability in water quality from catchment to catchment is too high for generalized conclusions to be made over the extent of the potential changes from site to site. The value of an organised campaign of opportunistic sampling using an infrastructure of enthusiastic staff from regionally dispersed organisations associated with environmental matters (in this case the forestry industry) is highlighted.

Description: A dynamic, process-based model of surface water acidification, MAGIC, has been applied to over a thousand sites across the UK. The model is calibrated to surface water samples collected during a survey for the Critical Loads programme, and utilises the best available and consistent estimates of soil physical and chemical properties, rainfall and runoff volumes, and deposition chemistry. A total of 698 sites were calibrated successfully. At these sites, surface water chemistry was reconstructed from 1850 to the present day, and forecast to 2050 based on future decreases in sulphur (S) deposition in response to the Second S Protocol. Model outputs capture distinct regional patterns of acidification and recovery. the most acidic present-day conditions are found in acid-sensitive regions of Northern England (the Pennines, Lake District and North York Moors). Although a significant proportion of sites in these areas failed to calibrate, those that did are predicted to have experienced severe historic decreases in acidic neutralising capacity (ANC) in response to high levels of acidic deposition. The model also indicates significant acidification in the moderate deposition areas of Wales and Galloway, whereas in the low deposition region of northern Scotland, acidification has been minor even in areas of acid-sensitive geology. ANC is forecast to recover at virtually all sites, with the greatest recovery predicted for areas currently subject to high deposition. The model indicates that the Second S Protocol, however, will not be sufficient to produce full recovery, with average ANC increases to 2050 counteracting just 27% of the simulated decline from 1850 to present day. Acidic conditions (ANC 〈 0) are predicted to persist until 2050 at a significant number of sites in Northern England, Wales and Galloway.

Description: An electrical circuit analogue of a river catchment is described from which is derived an hydrological model of river flow called the River Electrical Water Analogue Research and Development (REWARD) model. The model is based upon an analytic solution to the equation governing the flow of electricity in an inductance-capacitance-resistance (LCR) circuit. An interpretation of L, C and R in terms of catchment parameters and physical processes is proposed, and tested for the River Irwell catchment in northwest England. Hydrograph characteristics evaluated using the model are compared with observed hydrographs, confirming that the modelling approach does provide a reliable framework within which to investigate the impact of variations in model input data.

Description: The MERLIN model was applied on the results of a field-scale manipulation experiment with decreased nitrogen (N) deposition in an N saturated forest ecosystem in the Netherlands. The aim was to investigate the mechanisms that could explain the observed rapid response of nitrate as a result of the decreased N input. Calibrating the model to pre-treatment data revealed that, despite the high atmospheric N input, the trees relied on N mineralised from refractory organic matter (ROM) for their growth. MERLIN could simulate only the fast response of nitrate leaching after decreased input if this ROM mineralisation rate was decreased strongly at the time of the manipulation experiment.

Description: Dynamics of C and N in forest soils in the Nutrient Cycling and Soil Acidification Model (NUCSAM) are described by the transformation and decomposition of three organic matter compartments, litter, fermented material and humic material. These three compartments are allocated to the morphological distinguishable L, F and H horizons of the organic layer. Changes in the pools of these organic compartments are described with first order equations for decomposition and transformation. Rate constants for decomposition and transformation were derived by calibrating the model to measured organic matter pools in organic layers of a chrono-sequence of five first succession Scots pine stands between 15 and 120 years old. Simulated pools of organic matter in the organic layers were in agreement with measured pools in the five pine stands, except for the first thirty years of the H-horizon. During this period, an increase in organic matter in the H horizon was simulated while no H horizons were observed in the field. The simulated total pool of organic matter in the organic layer agreed well with values from a field inventory in 20 other Scots pine stands, but the simulated distribution over the three horizons differed from the field measurements which varied among sites. For the Scots pine stands the model was able to simulate the organic matter accumulation in the top 40-cm of the mineral soil; derived almost completely from fine root turnover. The accumulated pool of nitrogen in the organic layer was in agreement with measured pools for the oldest Scots pine stand but was too high for the younger stands. Especially, the accumulation of N in the F-horizon was too fast, presumably due to an overestimated retention of nitrogen.

Description: A simple dynamic soil model developed to analyse the effects of atmospheric deposition and nutrient cycling on terrestrial ecosystems, SMART 2, was applied to the Kangasvaara catchment in eastern Finland. Given the historical deposition and forest growth patterns and reasonable values for the input parameters, SMART 2 was calibrated successfully to reproduce present-day soil and Kangasvaara catchment on the soil and runoff water chemistry under a future deposition scenario (GRP scenario). These impacts were also compared to the effects of further reducing the deposition of sulphur and nitrate under the maximum feasible reduction (MFR) scenario. The model demonstrates the consequences of breaking the nutrient cycle, and predicts that final cutting results in increased leaching of inorganic nitrogen and base cations from the cut part of the catchment for about 10 years. The resulting concentrations in the stream will depend on the ability of the buffer zones surrounding the stream to capture and utilize these nutrients.

Description: The catchment scale-experiments of the RAIN and CLIMEX projects conducted on boreal forest ecosystems at Risdalsheia, southernmost Norway, provide a unique set of data on the flux of nitrogen (N) in runoff following changes in N deposition, carbon dioxide (CO2) level and temperature. MERLIN (Model of Ecosystem Retention and Loss of Inorganic Nitrogen), a recently-developed model that focuses on N leaching, provides a means by which these data can be placed into a quantitative framework. The features of the N flux in runoff at Risdalsheia to be explained include (1) leaching of about 30-50 mmol m-2 yr-1 (30-40% of N deposition) during the period 1985-1997 at reference catchments, (2) rapid and dramatic reduction in N leaching following experimental reduction in N deposition in 1985 at KIM catchment, (3) increased flux of about 5 mmol m-2 yr-1 following onset of 3-5°C warming and increased CO2 in 1995 at KIM catchment, and (4) increased flux of about 12 mmol m-2 yr-1 following 3-5°C warming of soil in 1995 at EGIL catchment. One set of calibrated model parameters is sufficient to simulate the changes in N runoff at both experimental catchments for both of the manipulations. The model support the conceptual picture of the soil as the major sink for N inputs from deposition with N accumulating in both the forest floor (labile organic matter LOM) and the bulk soil (refractory organic matter ROM). As the molar carbon/nitrogen (C/N) ratio of LOM decreases to below 23, progressively less N is immobilised and more goes to runoff. The model also supports the conceptual picture of increased rate of decomposition of old soil organic matter in response to higher temperature. An increase of 5% is sufficient to produce the 5-12 mmol m-2 yr-1 increase in N flux in runoff observed at the 2 experimental catchments. The MERLIN simulations are consistent with measurements of increase in net mineralisation rates (per catchment area by 70 mmol m-2 yr-1) and N contents in foliage in treated and reference areas before and after onset of treatment. Runoff provides a very sensitive indicator of changes in N cycling within the ecosystem. Small changes in key processes such as N mineralisation give rise to large relative changes in N flux. Uncertainties in measurements are generally much larger than changes indicated by the model calibration.

Description: A simple mass balance has been used to estimate soil calcium depletion during the growth of a 50 year old Sitka spruce crop on acid, base-poor peaty podzol soils in upland Wales. Growth of the crop will deplete the soil calcium reserve by an amount (205 kg Ca ha-1) approximately equivalent to the exchangeable calcium pool to the bottom of the profile and equal to 14% of the total soil calcium reserve to the bottom of the B horizon. Despite these predictions, measurements of exchangeable calcium show no differences beneath mature forest and acid grassland, implying that i) weathering rates in forest soils are greater than long-term estimates and predictions by the PROFILE soil chemistry model ii) the trees can access other sources of calcium or iii) there are significant errors in the mass balance. Following stem-only harvesting, growth of a 50 year old second rotation crop will lead to further depletion of soil calcium, but this amount (79 kg Ca ha-1), is less than for a second rotation crop following whole-tree harvesting (197 kg Ca ha-1). After the first crop, stem-only harvesting would allow a further 18 rotations before depletion of the total calcium reserve to the bottom of the B horizon. Whole-tree harvesting would allow for seven rotations after the first crop. These calculations assume that all sources of calcium are equally available to the crop. This can only be resolved by dynamic modelling of the calcium cycle at the ecosystem scale based on appropriate field measurements. The potential for significant soil acidification is therefore greater following whole-tree harvesting and, in line with current recommendations (Nisbet et al., 1997), this technique should probably be avoided on acidic, nutrient-poor soils unless remedial measures are included to enhance the soil base cation status.

Description: An order-of-magnitude argument shows that the different surface temperatures of soil and sparse vegetation affect carbon assimilation and soil respiration significantly. However, regulation of assimilation through associated modulation of in-canopy carbon dioxide levels is weak. It is shown that for many vegetation types, the use of a two-layer representation of vegetation is essential to predict, accurately, terrestrial carbon fluxes, primarily through allowing different surface energy balances.

Description: Rainfall interception losses were monitored for twelve months and related to vegetation and rainfall characteristics at the Wanariset Sangai on the upper reaches of the Mentaya river, Central Kalimantan. The rainfall interception losses were quantified for one hectare each of unlogged and logged humid tropical rainforests. The results show that interception loss is higher in the unlogged forest (11% of total gross rainfall) than in the logged forest (6%). Interception loss was also simulated by the modified Rutter model and Gash's original and revised models. Both the Rutter and revised Gash models predicted total interception loss over a long period adequately, and resulted in estimates of the interception loss that deviated by 6 to 14% of the measured values, for both the unlogged and logged plots.

Description: Distance from the sea, proximity of mountains, continentality and elevation are all useful covariates to assist the mapping of extreme rainfalls. Regression models linking these and other variables calculated from a digital terrain model have been built for estimating the median annual maximum rainfall, RMED. This statistic, for rainfall durations between 1 hour and 8 days, is the index variable in the rainfall frequency analysis for the new UK Flood Estimation Handbook. The interpolation of RMED between raingauge sites is most challenging in mountainous regions, which combine the greatest variation in rainfall with the sparsest network of gauges. Sophisticated variables have been developed to account for the influence of topography on extreme rainfall, the geographical orientation of the variables reflecting the prevailing direction of rain-bearing weather systems. The different processes of short and long-duration extreme rainfall are accounted for by separate regression models. The technique of georegression combines estimates from regression models with a map of correction factors interpolated between raingauge locations using the geostatistical method of kriging, to produce final maps of RMED across the UK.

Description: Data on the water quality of streams draining a range of acidic and acid sensitive, mainly afforested, upland catchments in mid- and north-Wales and northern-England are described to investigate the acidification effects of conifer harvesting in relation to natural variability. Most sites show a large range in pH and major cation and major anion concentrations. The waters draining from the smaller catchments are more acidic and aluminium bearing reflecting a higher proportion of runoff from the acidic soils in each area. However, there is often a less acidic component of runoff under base-flow conditions due to ground-water contributions particularly within the larger streams. Higher concentrations of nitrate occur for sites which have been felled although declines in concentration occur several years after felling. Multiple regression analysis reveals the importance of cation exchange and within catchment acidification associated with sulphate and nitrate generation. Sulphate also has a component associated with weathering but the patterns vary from catchment to catchment. Analysis of the influence of changing anion concentrations associated with tree harvesting reveals that the acidification induced by increases in nitrate can be offset or reversed by the lowering of chloride and sulphate concentrations due to decreased atmospheric scavenging by the vegetation, reduced evapotranspiration and increased surface runoff diluting the acidity generated. It is concluded that contemporary UK forestry guidelines with an emphasis on phased harvesting of catchments over several years and careful harvesting methodologies can alleviate most problems of stream acidification associated with felling activities and in some cases can reverse the acidification pattern.

Description: Bacteriophages are increasingly used as tracers for quantitative analysis in both hydrology and hydrogeology. The biological particles are neither toxic nor pathogenic for other living organisms as they penetrate only a specific bacterial host. They have many advantages over classical fluorescent tracers and offer the additional possibility of multi-point injection for tracer tests. Several years of research make them suitable for quantitative transport analysis and flow boundary delineation in both surface and ground waters, including karst, fractured and porous media aquifers. This article presents the effective application of bacteriophages based on their use in differing Swiss hydrological environments and compares their behaviour to conventional coloured dye or salt-type tracers. In surface water and karst aquifers, bacteriophages travel at about the same speed as the typically referenced fluorescent tracers (uranine, sulphurhodamine G extra). In aquifers of interstitial porosity, however, they appear to migrate more rapidly than fluorescent tracers, albeit with a significant reduction in their numbers within the porous media. This faster travel time implies that a modified rationale is needed for defining some ground water protection area boundaries. Further developments of other bacteriophages and their documentation as tracer methods should result in an accurate and efficient tracer tool that will be a proven alternative to conventional fluorescent dyes.

Description: A practical methodology for distributed rainfall-runoff modelling using grid square weather radar data is developed for use in real-time flood forecasting. The model, called the Grid Model, is configured so as to share the same grid as used by the weather radar, thereby exploiting the distributed rainfall estimates to the full. Each grid square in the catchment is conceptualised as a storage which receives water as precipitation and generates water by overflow and drainage. This water is routed across the catchment using isochrone pathways. These are derived from a digital terrain model assuming two fixed velocities of travel for land and river pathways which are regarded as model parameters to be optimised. Translation of water between isochrones is achieved using a discrete kinematic routing procedure, parameterised through a single dimensionless wave speed parameter, which advects the water and incorporates diffusion effects through the discrete space-time formulation. The basic model routes overflow and drainage separately through a parallel system of kinematic routing reaches, characterised by different wave speeds but using the same isochrone-based space discretisation; these represent fast and slow pathways to the basin outlet, respectively. A variant allows the slow pathway to have separate isochrones calculated using Darcy velocities controlled by the hydraulic gradient as estimated by the local gradient of the terrain. Runoff production within a grid square is controlled by its absorption capacity which is parameterised through a simple linkage function to the mean gradient in the square, as calculated from digital terrain data. This allows absorption capacity to be specified differently for every grid square in the catchment through the use of only two regional parameters and a DTM measurement of mean gradient for each square. An extension of this basic idea to consider the distribution of gradient within the square leads analytically to a Pareto distribution of absorption capacity, given a power distribution of gradient within the square. The probability-distributed model theory (Moore, 1985) can then be used directly to obtain the integrated runoff production for the square for routing to the catchment outlet. justification for the simple linkage function is in part sought through consideration of variants on the basic model where (i) runoff production is based on a topographic index control on saturation and (ii) absorption capacity is related to the Integrated Air Capacity of the soil, as obtained from soil survey. An impervious area fraction is also introduced based on the use of Landsat classified urban areas. The Grid Model and its variants are assessed in Part 2 (Bell and Moore, 1998), first as simulation models and then as forecasting models, following the development of updating procedures to accommodate recent observations of flow so as to improve forecast performance in a real-time context.

Description: The Coalburn experimental catchment, located in the Kielder Forest in northern Britain, was established in 1967 to study the hydrological impacts of upland coniferous plantation forestry. Results of 30 years' study (1967–96) are presented; they cover the transformation of the catchment from rough grazing through drainage and planting with conifers in 1972–73 and the subsequent forest development to canopy closure. In the early years of forest growth, the pre-planting forestry drainage dominated the hydrology and the observed changes were quite different from those normally associated with forestry; catchment evaporation was reduced, stream stormflow response times were shortened and dry weather baseflows were enhanced. These effects were sustained for an unexpectedly long period-up to one half of the forest plantation cropping cycle - before being reversed by the increasing influence of the growing forest. These results indicate that significant areas of young plantation forests may function hydrologically in ways very different from what is generally assumed from studies of mature forests. For large plantations, a mixed age forest structure may have hydrological as well as environmental advantages.

Description: Capacitance probes are a fast, safe and relatively inexpensive means of measuring the relative permittivity of soils, which can then be used to estimate soil water content. Initial experiments with capacitance probes used empirical calibrations between the frequency response of the instrument and soil water content. This has the disadvantage that the calibrations are instrument-dependent. A twofold calibration strategy is described in this paper; the instrument frequency is turned into relative permittivity (dielectric constant) which can then be calibrated against soil water content. This approach offers the advantages of making the second calibration, from soil permittivity to soil water content. instrument-independent and allows comparison with other dielectric methods, such as time domain reflectometry. A physically based model, used to calibrate capacitance probes in terms of relative permittivity (εr) is presented. The model, which was developed from circuit analysis, predicts, successfully, the frequency response of the instrument in liquids with different relative permittivities, using only measurements in air and water. lt was used successfully to calibrate 10 prototype surface capacitance insertion probes (SCIPS) and a depth capacitance probe. The findings demonstrate that the geometric properties of the instrument electrodes were an important parameter in the model, the value of which could be fixed through measurement. The relationship between apparent soil permittivity and volumetric water content has been the subject of much research in the last 30 years. Two lines of investigation have developed, time domain reflectometry (TDR) and capacitance. Both methods claim to measure relative permittivity and should therefore be comparable. This paper demonstrates that the IH capacitance probe overestimates relative permittivity as the ionic conductivity of the medium increases. Electrically conducting ionic solutions were used to test the magnitude of this effect on the determination of relative permittivity. The response was modelled so that the relative permittivity, independent of ionic conductivity, could be determined in solutions with an electrical conductivity of up to 0.25 S m-1. It was found that a solution EC of less than 0.05 S m-1 had little impact on the permittivity measurement.

Description: The aim of this paper is to improve the representation of root water uptake in the land surface scheme SECHIBA coupled to the LMD General Circulation Model (GCM). Root water uptake mainly results from the interaction between soil moisture and root profiles. Firstly, one aspect of the soil hydrology in SECHIBA is changed: it is shown that increasing the soil water storage capacity leads to a reduction in the frequency of soil water drought, but enhances the mean evapotranspiration. Secondly, the representation of the soil-vegetation interaction is improved by allowing a different root profile for each type of vegetation. The interaction between sub-grid scale variabilities in soil moisture and vegetation is also studied. The approach consists of allocating a separate soil water column to each vegetation type, thereby 'tiling' the grid square. However, the possibility of choosing the degree of soil moisture spatial heterogeneity is retained. These enhancements of the land surface system are compared within a number of GCM experiments.

Description: The continuing development of computational fluid dynamics is allowing the high resolution study of hydraulic and sediment transport processes but, due to computational complexities, these are rarely applied to areas larger than a reach. Existing approaches, based upon linked cross sections, can give a quasi two-dimensional view, effectively simulating sediment transport for a single river reach. However, a basin represents a whole discrete dynamic system within which channel, floodplain and slope processes operate over a wide range of space and time scales. Here, a cellular automaton (CA) approach has been used to overcome some of these difficulties, in which the landscape is represented as a series of fixed size cells. For every model iteration, each cell acts only in relation to the influence of its immediate neighbours in accordance with appropriate rules. The model presented here takes approximations of existing flow and sediment transport equations, and integrates them, together with slope and floodplain approximations, within a cellular automaton framework. This method has been applied to the basin of Cam Gill Beck (4.2 km2 ) above Starbotton, upper Wharfedale, a tributary of the River Wharfe, North Yorkshire, UK. This approach provides, for the first time, a workable model of the whole basin at a 1 m resolution. Preliminary results show the evolution of bars, braids, terraces and alluvial fans which are similar to those observed in the field, and examples of large and small scale non-linear behaviour which may have considerable implications for future models.

Description: Nitrogen processes are now included in a new version of MAGIC (version 7), a process-oriented catchment-scale model for simulating runoff chemistry. Net retention of nitrogen (N) is assumed to be controlled by plant uptake and the carbon/nitrogen (C/N) ratio of soil organic matter, the latter as evidenced by empirical data from forest stands in Europe. The ability of this version of MAGIC 7 to simulate and predict inorganic N concentrations in runoff is evaluated by means of data from whole-ecosystem manipulation experiments at Aber, Wales, UK, (nitrogen addition as part of the NITREX project) and Risdalsheia, Norway (exclusion of acid deposition as part of the RAIN project and climate change as part of the CLIMEX project). MAGIC 7 simulated the changes in N leaching satisfactorily as well as changes in base cations and acid neutralising capacity observed at these two sites. MAGIC 7 offers a potential tool for regional assessments and scenario studies of the combined effects of acid deposition, land-use and climate change.

Description: Very short-term rainfall forecasting models designed for runoff analysis of catchments, particularly those subject to flash-floods, typically include one or more variables deduced from weather radars. Useful variables for defining the state and evolution of a rain system include rainfall rate, vertically integrated rainwater content and advection velocity. The forecast model proposed in this work complements recent dynamical formulations by focusing on a formulation incorporating these variables using volumetric radar data to define the model state variables, determining the rainfall source term directly from multi-scan radar data, explicitly accounting for orographic enhancement, and explicitly incorporating the dynamical model components in an advection-diffusion scheme. An evaluation of this model is presented for four rain events collected in the South of France and in the North-East of Italy. Model forecasts are compared with two simple methods: persistence and extrapolation. An additional analysis is performed using an existing mono-dimensional microphysical meteorological model to produce simulated rain events and provide initialization data. Forecasted rainfall produced by the proposed model and the extrapolation method are compared to the simulated events. The results show that the forecast model performance is influenced by rainfall temporal variability and performance is better for less variable rain events. The comparison with the extrapolation method shows that the proposed model performs better than extrapolation in the initial period of the forecast lead-time. It is shown that the performance of the proposed model over the extrapolation method depends essentially on the additional vertical information available from voluminal radar.

Description: In the framework of simplified water balance models devoted to irrigation scheduling or crop modelling, the relative transpiration rate (the ratio of actual to maximal transpiration) is assumed to decrease linearly when the soil dries out below a critical available water value. This value is usually expressed as a fraction, F, of the maximal available soil water content. The present work aims to use the basic laws governing water transfer through the plants at a daily time step to compute F dynamically as the crop grows. It can be regarded as an expansion of Slabbers' (1980) approach to crop growing conditions. Starting from the mathematical representation given by single-root models (Gardner, 1960), an analytical expression for F is derived, using simplified hypotheses. This expression accounts for plant attributes such as the mean root radius, the critical leaf water potential for stomatal closure and the root length density profile growing with the crop. Environmental factors such as soil type and atmospheric demand also influence F. The structural influence of soil comes from the required introduction of the bulk soil hydraulic conductivity in the single-root model. The shape of the root length density profile is assumed to be sigmoidal and a new profile is calculated at each value of the rooting depth. A sensitivity analysis of F to all those factors is presented. The first general result is that F decreases as the root system grows in depth. Differences in the shape of the root profile can be responsible for differential water stress sensitivity in the early stages of growth. Yet, low critical leaf water potential can compensate partially for a poor root profile. Conversely, F is relatively insensitive to the average root radius. F sensitivity to soil type seems somewhat artificial: given the bulk soil hydraulic conductivity formula, the soil sensitivity results from F being expressed as a fraction of the maximal available soil water content. The atmospheric demand together with the rooting depth appear as the most important factors. However, when assuming predictable climatic and crop evolution, compensation occurs between those two effects leading to a relative stability of F when the crop is fully developed. Though relying on well-known physical laws, the present approach remains in the framework of single layer models with the same limitations.

Description: Chronic deposition of inorganic nitrogen (N) compounds from the atmosphere to forested ecosystems can alter the status of a forest ecosystem from N-limited towards N-rich, which may cause, among other things, increased leaching of inorganic N below the rooting zone. To assess the time aspects of excess N leaching, a process-oriented dynamic model, MERLIN (Model of Ecosystem Retention and Loss of Inorganic Nitrogen), was tested on an N-manipulated catchment at Gårdsjön, Sweden (NITREX project). Naturally generated mature Norway spruce dominates the catchment with Scots pine in drier areas. Since 1991, ammonium nitrate (NH4NO3) solution at a rate of about 35 kg N ha-1 yr-1 (250 mmol m-2 yr-1) has been sprinkled weekly, to simulate increased atmospheric N deposition. MERLIN describes C and N cycles, where rates of uptake and cycling between pools are governed by the C/N ratios of plant and soil pools. The model is calibrated through a hindcast period and then used to predict future trends. A major source of uncertainty in model calibration and prediction is the paucity of good historical information on the specific site and stand history over the hindcast period 1930 to 1990. The model is constrained poorly in an N-limited system. The final calibration, therefore, made use of the results from the 6-year N addition experiment. No independent data set was available to provide a test for the model calibration. The model suggests that most N deposition goes to the labile (LOM) and refractory (ROM) organic matter pools. Significant leaching is predicted to start as the C/N ratio in LOM is reduced from the 1990 value of 35 to

Description: Great effort has been dedicated to developing soil acidification models for use on different scales. This paper focuses on the changes in model performance of a site scale soil acidification model (NUCSAM) and a national to European scale soil acidification model (SMART 2). This was done to gain insight into the effects of model simplification. Because these models aim to predict the response to reduction in acid deposition, these models must be tested under such circumstances. A straightforward calibration and validation of the regional model, however, is hampered by lack of observations over a sufficient time period. Consequently, NUCSAM was calibrated and validated to a manipulation experiment involving reduced acid deposition in the Speuld forest, the Netherlands. SMART 2 was then used with calibrated input data from NUCSAM. The acid deposition was excluded by a roof beneath the canopy. The roofed area consists of a plot receiving pristine deposition levels of nitrogen (N) and sulphur (S) and a control plot receiving ambient deposition. NUCSAM was calibrated on the ambient plot, followed by a validation of both models on the pristine plot. Both models predicted soil solution concentrations within the 95% confidence interval of the observed responses for both the ambient plot and the pristine plot at 90 cm depth. Despite the large seasonal and vertical (spatial) variation in soil solution chemistry, the trends in annual flux- weighted soil solution chemistry, as predicted by SMART 2 and NUCSAM, corresponded well.The annual leaching fluxes below the root zone were also similar although differences exist for the topsoil. For the topsoil, NUCSAM simulated the nutrients and acid related constituents better than SMART 2. Both models overestimated the ammonium (NH4) concentration at 10 cm depth. SMART 2 underestimated calcium and magnesium (BC2+) concentration at 10 depth, whereas NUCSAM overestimated BC2+ concentration at 90 cm depth. NUCSAM predicted the effect of deposition reduction on N concentrations at both depths, whereas SMART 2 underestimated the effect of deposition reduction at 10 cm depth. Both models predicted faster effects of deposition reduction on aluminum (Al), sulphate (SO4) and base cations than was observed. Generally, it appeared that the differences were large during the period of profound deposition changes whereas small differences occurred during slight variations in deposition level. It is concluded that a simpler model description does not affect the model's performance significantly as regards flux-weighted annual average concentrations at greater depth. Model improvements must focus on processes related to N-dynamics.

Description: This paper describes a strategic approach for providing documentation of the surface energy exchange for heterogeneous land surfaces via the simultaneous, four-dimensional assimilation of several streams of remotely sensed data into a coupled land surface-atmosphere model. The basic concepts and underlying theory behind this proposed approach are presented with the intent that this will guide, facilitate, and stimulate future research focused on its practical implementation when appropriate data from the Earth Observing System (EOS) become available. The theoretical concepts that underlie the approach are derived from relationships between the values of parameters which control surface exchanges at pixel (or patch) scale and the area-average value of equivalent parameters applicable at larger, grid scale. A three-step implementation method is proposed which involves (a) estimating grid-average surface radiation fluxes from appropriate remotely sensed data; (b) absorbing these radiation flux estimates into a four-dimensional data assimilation model in which grid-average values of vegetation-related parameters are calculated from pertinent remotely sensed data using the equations that link pixel and grid scales; and (c) improving the resulting estimate of the surface energy balance-again using scale-linking equations by estimating the effect of soil-moisture availability, perhaps assuming that cloud-free pixels are an unbiased subsample of all the pixels in the grid square.

Description: Surveys of 485 lakes in Norway conducted in 1986 and again in 1995 reveal widespread chemical recovery from acidification. Sulphate concentrations in lakes have decreased by 40% in acidified areas in southern Norway. This decrease has been compensated about 25% by decreases in concentrations of base cations and of 75% by increased Acid Neutralising Capacity (ANC). The increased ANC in turn reflects lower concentrations of acidic cations Aluminum (ALn+) and Hydrogen (H+). A sub-set of 78 of the 485 lakes sampled yearly between 1986 and 1997 shows that, at first most of the decrease in non-marine sulphate (SO4*) was compensated by a decrease in base cations, such that ANC remained unchanged. Then as SO4* continued to decrease, the concentrations of non- marine calcium and magnesium ((Ca+Mg)*) levelled out. Consequently, ANC increased, and H+ and Aln+ started to decrease. In eastern Norway, this shift occurred in 1989–90, and came slightly later in southern and western Norway. Similar shifts in trends in about 1991–92 can also be seen in the non-acidified areas in central and northern Norway. This shift in trends is not as pronounced in western Norway, perhaps because of the confounding influence of sea-salt episodes on water chemistry. This is the first documented national-scale recovery from acidification due to reduced acid deposition. Future climate warming and potentially increased N-leaching can counteract the positive trends in recovery from acidification.

Description: In the Speuld forest, the Netherlands, the dynamic soil acidification model NuCSAM has been applied to a manipulation experiment in which part of the forest was roofed to control nitrogen (N) and sulphur (S) deposition. The roofed area was divided into two subplots watered artificially; one received ambient N and S deposition and one with pristine N and S deposition. Concentration measurements on each plots showed a high (time-dependent) spatial variability. Statistical analyses of the concentrations on both subplots showed small but significant effects of the reduction in deposition on nitrate (NO3) sulphate (SO4) and aluminum (Al) concentrations. The statistical significance of the effects was minimised by the large spatial variability within the plots. Despite these shortcomings, simulated concentrations were generally within the 95% confidence interval of the measurements although the effect of a reduction in N deposition on soil solution chemistry was underestimated due to a marked decline in N-uptake by the vegetation.

Description: The withdrawal of water from soil by vegetation, which in steady state conditions is equivalent to the transpiration rate, can be written in terms of water potential in the form of an Ohm's law analogy, known as van den Honert's equation: The difference between an effective soil water potential and the bulk canopy water potential is divided by an effective soil-plant resistance. This equation is commonly used, but little is known about the precise definition of its parameters. The issue of this paper is to bridge the gap between the bulk approach and a multi-layer description of soil-plant water transfer by interpreting the bulk parameters in terms of the characteristics of the multi-layer approach. Water flow through an elementary path within the soil or the root is assumed to follow an Ohm's law analogy, and the soil and root characterisics are allowed to vary with depth. Starting from the basic equations of the multi-layer approach, it is proved that the total rate of transpiration can also be expressed in the form of an Ohm's law analogy. This means that van den Honert's equation holds at canopy scale, insofar as the assumptions made on the physics of root water uptake hold. In the bulk formulation derived, the effective soil-plant resistance appears as a combination of the elementary resistances making up the multi-layer model; and the effective soil water potential is a weighted mean of the water potentials in each soil layer, the weighting system involving the complete set of elementary resistances. Simpler representations of soil-plant interaction leading to Ohm's law type formulations are also examined: a simplified multi-layer model, in which xylem (root axial) resistance is neglected, and a bulk approach, in which soil-root interaction is represented by only one layer. Numerical simulations performed in different standard conditions show that these simpler representations do not provide accurate estimates of the transpiration rate, when compared to the values obtained by the complete algorithm.

Description: Dryland salinity poses a major threat to agricultural production in the wheatbelt of Western Australia and much time and effort is expended on understanding the mechanisms which cause it and on developing techniques to halt or reverse its development. Whilst the location of much dryland salinity can be explained by its topographic position, a significant proportion of it cannot. This study investigated the hypothesis that major faults in the Yilgarn Craton represented in aeromagnetic data by intense curvilinear lows explained the location of areas of dryland salinity not explained by topography. Moreover, the causal mechanisms that might underpin a spatial relationship between major faults and dryland salinity were sought. In one fourth order catchment, nearly 85% of the salinity that was not explained topographically was within 2km of the centre line of a major fault, the remaining 15% being in the other 12km of the catchment. Three groups of similar third order catchments in the western wheatbelt of Western Australia were also investigated; in each case the catchment that was underlain by a major fault had dryland salinity an order of magnitude more than the unfaulted catchment(s). This evidence demonstrates a strong spatial association between major faults and the development of dryland salinity. Other evidence suggests that the underlying mechanism is hydraulic conductivity 5.2 to 2.9 times higher inside the fault zone compared to outside it and shows that geomorphology, salt store, regolith thickness, and degree of clearing are not the underlying mechanisms. In one of the groups of catchments, it has been calculated that an amount of recharge, significant in relation to recharge from rainfall, was entering from an adjacent catchment along a major fault. The paper concludes that geological features such as major faults affect the development of dryland salinity in the wheatbelt of Western Australia because of permeability differences in the regolith and therefore computer models of salinity risk need to take these differences into account. Techniques need to be developed to map, quickly and relatively cheaply, the geology-related permeability differences over wide areas of the landscape.

Description: European concerns about the consequences of anthropogenic impacts on environmental quality have led to the establishment of various dynamic modelling approaches through which the consequences of impacts over time can be assessed. Similarly, throughout Europe, there has been extensive collection of regional data on "environmental capital" resulting in the production of wide area mapping of environmental quality (soils, land use etc). The aim of the DYNAMO was to integrate data and models, specifically; (1) to enhance the existing process based models to evaluate the impacts of multiple drivers of environmental change; (2) to evaluate these models at intensively studied (and manipulated) catchments and stands; (3) to scale up in time from observations collected over several years to predict the long term impacts over decades, and (4) to scale up in space from the individual site level to regional, National and European scale. The project aims to develop and enhance regional modelling approaches so that European scale impacts of acidic deposition, land use (forestry practices) and global change can be determined without compromising process level understanding of ecosystem function. The DYNAMO project contributes to the EU TERI (Terrestrial Ecosystems Research Initiative) framework of the Environment and Climate Programme of the European Commission.

Description: An easily constructed and installed instrument for measuring colocated soil temperature and resistance profiles is described. Minimum disturbance to the soil structure is achieved. The system indicates the melting front of permafrost at a high Arctic field site and shows the effect and extent of summer rainfall events upon the soil water profile. The system is capable of long-term recording of soil moisture profiles at a frequency commensurate with eddy correlation measurements of the surface fluxes of water vapour and carbon dioxide; it thus provides the information necessary for understanding the processes involved in the soil-atmosphere exchange of water and carbon dioxide.

Description: Analytical and numerical solutions are obtained for dispersion of pollutants along unsteady groundwater flow in a longitudinal direction through semi-infinite aquifers the permeability of which is either uniform or varies with position. Sources of pollution are both a concentrated point input at the origin and a spatially distributed background source. One expression chosen to represent the seasonal pattern of the time dependent velocity is sinusoidal behaviour over a year. The solutions obtained predict the time and distance from the location at which an input concentration is introduced at which the pollution concentration becomes harmless. Also, the time period for rehabilitating a polluted aquifer for human use can also be assessed.

Description: Triserial planktonic foraminiferal species from the Palaeogene are classified into the Early Danian Guembelitria, with pore mounds on the test surface, and the Early Eocene-Late Oligocene Jenkinsina, which are also microperforate but lack pore mounds. The stratigraphic and palaeogeographic ranges are discussed, the holotype of G. cretacea Cushman (the type species of Guembelitria) is re-illustrated, and neotypes designated for G. danica (Hofker) and Jenkinsina triseriata (Terquem). Chiloguembelitria is shown to be a junior synonym of Guembelitria.

Description: Four species of the genus Boltovskoyella Malumián & Masiuk are recognized in Patagonia, among them, B. paleocenica sp. nov., which is described from Danian shallow marine sediments. Considering that the previous records of Boltovskoyella are from the Middle-Late Eocene, this new species represents the oldest known occurrence of the genus. Boltovskoyella seems to be endemic to Patagonia, shows opportunistic features and prefers temperate-warm water settings.

Description: A new Permian (Late Asselian–Dorashamian) ostracod fauna (66 species belonging to 35 genera) from Hydra Island (Greece) is described. Twelve new species are described: Hollinella (P.) hydraensis Crasquin-Soleau n.sp, Bairdia episkopiensis Crasquin-Soleau n.sp., Bairdia rigasensis Crasquin-Soleau n.sp., Bairdia thikiaensis Crasquin-Soleau n.sp., Chamishaella marmariensis Crasquin-Soleau n.sp., Cypridina gussevaae Crasquin-Soleau n.sp., Cyathus barmariensis Crasquin-Soleau n.sp., Cyathus klimakiensis Crasquin-Soleau n.sp., Bairdiacypris bistiensis Crasquin-Soleau n.sp., Shishaella hellenensis Crasquin-Soleau n.sp., Bairdia ishizakii Crasquin-Soleau n.sp., Petasobairdia kozuri Crasquin-Soleau n.sp. Forty-four other species are figured. This assemblage is characteristic of a shallow water platform. The palaeobiogeographic relationships are presented and represent significant additions to the Permian Palaeo-Tethyan ostracod faunas.

Description: Mashkovia is one of the provincial conodonts which developed during late Famennian time in the cratonic regions of Russia. In this study, the taxonomy of this genus is revised, based on diagnostic characters of the Pa elements, such as the morphology of the anterior part of the platform, the ornamentation and the shape of the secondary keels. As a consequence, four species, including M. silesiensis n. sp. now discovered in Upper Silesia of southern Poland, are distinguished. The apparent absence of Mashkovia from North America, Variscan Europe, Australia and Africa cannot be simply explained by using temperature or other global climatic factors as a reason for the provincialism. Currents and/or local palaeoecologic factors were probably more important in controlling the distribution of these conodonts.

Description: A combined geochemical and micropalaeontological study of the late Albian ‘Amadeus Segment’ of the Aptian–Albian organic-rich Scisti a Fucoidi Formation in central Italy shows that planktic foraminiferal assemblages record changes in abundance and composition which are markedly related to CaCO3 and Total Organic Carbon content of the sediments. The distribution pattern of different genera seems to record changes in nutrient supply and surface water temperature. Changes in palaeoceanographic regime are also reflected in abundance, composition and trophic structure of benthic foraminiferal assemblages as a response to variations of oxygen content and organic flux to the sea floor.

Description: Preserved valves of fossil glochidia have been recovered from Holocene lake marls at Quidenham Mere, UK. Detailed morphological comparisons with glochidia removed from live adult unionids have enabled confident identification of the fossil glochidia as those of Anodonta anatina. Fossil glochidia are potentially powerful tools in the interpretation of palaeoenvironments. Different species of freshwater mussels are known to release glochidia at different times of the year and, therefore, the occurrence of fossil glochidia can provide information on the season during which sediments accumulated. Furthermore, glochidia can provide information on the presence of certain fish species and on water depth.

Description: In order to establish the relationship between the smooth, microperforate praehedbergellid forms of the genus Blefuscuiana with the younger, macroperforate and muricate forms typical of Hedbergella, two similar taxa but with the different characters of the two genera, are studied here: Blefuscuiana praetrocoidea (Kretchmar & Gorbachik) and its descendant Hedbergella trocoidea (Gandolfi), the type species of Hedbergella, and which typifies the Hedbergellidae.B. praetrocoidea was only found in the Early Aptian in the North Tethys. H. trocoidea ranges from the Late Aptian to Early Albian (?M. Albian) and is a cosmopolitan species. It evolves into Ticinella roberti (Gandolfi), a Late Aptian–Albian species with fused portici. The evolution of the Praehedbergellidae into the Hedbergellidae appears to be related to a relative sea-level rise in the Late Aptian and Albian (and the opening of the Proto-Atlantic) which provided a number of deep-water niches which the Hedbergellidae occupied.

Description: Late Middle Miocene (Upper Badenian) strata of the Fore-Carpathian Depression of Poland yield a shallow-water ostracod fauna which contains the species Triebelina raripila (G. W. Müller, 1894) and Carinocythereis carinata (Roemer, 1838). The palaeobiogeographic distribution of the two main species suggests, that in the late Middle Miocene, Central Paratethys was still connected to the Mediterranean, although still separated from the Eastern Paratethys and from southeastern Eurasia. The continuous occurrence of Triebelina raripila and Carinocythereis carinata in the Mediterranean basins, from the Early Miocene to Recent, indicates that marine conditions existed throughout, thereby allowing them to survive the Late Miocene salinity crisis.

Description: Odontochitina tabulata, a new tabulated ceratioid species, has been recorded and described from core samples in Well C3-65 in the SE Sirte Basin. This species is characterizd by parasutural and pandasutural features reflecting clear gonyaulacacean paratabulation. It has a short stratigraphic range and is considered as a valuable stratigraphic marker for the Late Santonian–Early Campanian. The diagnosis of the genus Odontochitina Deflandre, 1935 is emended to include forms having a well defined gonyaulacacean paratabulation and narrow pandasutural and parasutural ridges.

Description: Well-preserved Lower Mississippian (Dinantian) miospore assemblages have been recovered from the upper Cuyahoga Formation (type Wooster Member) and overlying lower Logan Formation (Byer Member) at two localities in Wayne County, northeastern Ohio, USA. All six samples were productive and yielded assemblages that represent the middle Tournaisian Spelaeotriletes pretiosus–Raistrickia clavata (PC) Miospore Biozone of Western Europe including a new species of trilete, acamerate miospore, Mooreisporites streelii, described from the Wooster Shale. Significant numbers of latest Devonian and earlier Carboniferous miospores are reworked into all assemblages. The palynological evidence is consistent with a late Kinderhookian age for most of the Cuyahoga Formation, including its well known ammonoid fauna. However, the position of the boundary between the Kinderhookian and Osagean Series remains uncertain.

Description: The integrated use of calcareous nannofossil and dinoflagellate cyst events in a study of the late Pliensbachian–early Toarcian interval in central Italy has yielded a high resolution biostratigraphy. The use of both the first and last occurrences of selected taxa belonging to the two phytoplankton groups allows the dating of the sediments with a very refined detail, even when lithologies are unfavourable to the preservation of one fossil group. The evolutionary history of calcareous nannofossils and dinoflagellate cysts during the early Jurassic and its links with global events are responsible for the high potential of this integrated biostratigraphy.

Description: Two new species, Parkiella angulocamerata sp. nov. and P. globocamerata sp. nov., are described from the Late Cretaceous (late Maastrichtian) Central Pacific Ocean, DSDP Sites 465 and 171. Examination under the SEM revealed apertural features that were not documented in the original description of Parkiella. An ‘L’-shaped aperture was originally considered as a diagnostic character of Parkiella; we suggest that this is a preservational artefact and question its diagnostic value. The existence of internal toothplates determine both Parkiella described here as members of the family Turrilinidae Cushman 1927. Both species were found to be endemic to the tropical Pacific Ocean. They occurred in sequence throughout the Maastrichtian section at Site 465 with a minimum (one sample) stratigraphic overlap. Parkiella globocamerata is one of the few deep-sea benthic foraminiferal species that indeed became extinct at the Cretaceous/Palaeogene (K/Pg) boundary. However, we document a decrease in both relative abundance and accumulation rate of the species already prior to the K/Pg transition. We propose that the interval between the LO (Last Occurrence) of P. angulocamerata and the LO of P. globocamerata is indicative of uppermost Cretaceous (Micula prinsii Zone) strata in the tropical Pacific.

Description: A systematic study on the evolution and stratigraphic distribution of the species of Catinaster from several DSDP/ODP sites with magnetostratigraphic records is presented. The evolution of Catinaster from Discoaster is established by documentation of a transitional nannofossil species, Discoaster transitus. Two new subspecies, Catinaster coalitus extensus and Catinaster calyculus rectus are defined which appear to be intermediates in the evolution of Catinaster coalitus coalitus to Catinaster calyculus calyculus. The first occurrence of C. coalitus is shown to be in the lower part of C5n.2n at 10.7–10.9 Ma in the low to mid–latitude Atlantic and Pacific Oceans. The last occurrence of C. coalitus coalitus varies from the upper part of C5n.2n to the lower portion of C4A. Magnetobiostratigraphic evidence suggests that the FO of C. calyculus rectus is diachronous. Catinaster mexicanus occurs in the late Miocene and has been found only in the eastern equatorial Pacific, the Indian Ocean and the Gulf of Mexico.

Description: Sixteen box core samples of Recent sediment collected in three transects across the East Greenland shelf and slope were analysed for Ostracoda. The samples which range in depth from 274 m to 3355 m, yielded a total of 52 species belonging to 25 genera. No less than 26 of the species also occur in the adjacent Scoresby Sund fjord complex. The fauna represents an interesting mixture of high latitude shallow water Arctic species and others known from bathyal and abyssal depths in the North Atlantic, including some pandemic deep sea species. Many species occur in shallower water here than in the North Atlantic due to the colder water. The fauna comprised of three associations (Shelf/Upper Slope; Slope: Lower Slope/Abyss). A marked faunal turnover occurs at the Upper Slope. The study raises questions concerning the constancy and universality of the relationship between certain ostracod species and water masses.

Description: INTRODUCTIONBy far the most widely available computer programs for recording, manipulating, and displaying numerical data are spreadsheets, such as Microsoft Excel™ and Lotus 1-2-3™. These are powerful and flexible tools and for most workers this is an obvious way of recording micropalaeontological data. However, they have been primarily produced for business users and have limited abilities when it comes to plotting scientific graphs. This note describes some indirect but rapid methods, for using the standard graphing tools in such packages, to produce additional types of graphs of value to micropalaeontologists.STACKED HISTOGRAM CHARTSFigure 1 is a stacked histogram chart, produced in Microsoft Excel™. This type of diagram is useful, for instance, in displaying variations in size of a species between samples through a section. Stacked histogram charts are not directly supported by any spreadsheets that I have seen. As a result, they can usually only be produced by rather inefficient techniques. For example, making a separate chart for each sample and then combining them in a graphics program. The indirect approach used here is to separate each true data series with a mirror image padding data series, which is not displayed. The entire diagram is then plotted as a single chart. The steps for doing this are:(1) Enter the data (specimens per size class) in a spreadsheet (samples v. size classes).(2) Between each pair of data columns insert a column with equations which will calculate mirror image padding data. These will have the form C3 = . . .

Description: Pliensbachian and Toarcian Ostracoda first described by Exton (Geological Paper, Carleton University, Ottawa, 79: 1–104 1979) from the Lusitanian Basin, west-central Portugal have been re-examined. As a result, a greater diversity in the Ostracoda (80 species) is now recognized. Two species are newly described (Eucytherura zambujalensis sp. nov., Ektyphocythere mediodepressa sp. nov.) from the marls and calcareous shales of the Maria Pares Hill section near the village of Zambujal. Poor preservation precludes a complete taxonomic review of the present material. Five ostracod zones are proposed; Gammacythere ubiquita–Ogmoconchella gruendeli Zone, Poly cope cerasia–Polycope cincinnata Zone, Liasina lanceolata–Ogmoconcha convexa Zone, Bairdiacypris rectangularis–Kinkelinella sermoisensis Zone, and Cytherella toarcensis-Kinkelinella costata Zone. Although the ostracod assemblages possess strong similarities to those described from Northwest Europe, some of the Zambujal assemblages are dominated by the genus Polycope. A marked faunal turnover, in association with the extinction of the Metacopina occurs in the lower Subzone of the tenuicostatum Zone of Lower Toarcian age. These faunal events are discussed in relation to changing environmental conditions.

Description: The conception that the substratum of the "Lockerbraunerde" of the Hohe Vogelsberg Mountains should represent a Late-Pleistocene, periglacial aeolian sediment, is rejected. It is demonstrated primary by means of radio carbon-datings of fossil Ah-horizons that a large portion of this substratum consists of anthropogenic colluvium. Its development occured most likely already during the earlier Holocene. The findings that the "Deckschutt" and also the substratum of the "Lockerbraunerde" are representing contemporaneous developments of the Younger Dryas are substantiated,

Description: Vor etwa 35 000-40 000 Jahren schuf eine Episode neotektonischer Aktivität an der Indus-Sutur bei Lamayuru (Ladakh) einen See, von dem eine über 105 m mächtige Abfolge fluviolakustriner Ablagerungen erhalten ist. Die zwischen Ton/Silt/Sand eingelagerten lakustrinen Horizonte (Kalkschlämme) und karbonatreichen Schichten haben Süßwasser-Ostrakoden, Gastropoden und Charophyten geliefert. Insgesamt wurden 9 Fossilhorizonte angetroffen. Die hauptsächlichen Ostrakodentaxa sind llyocypris (l. gibba und I. bradyi), Eucypris und Candona. Bei den Gastropoden dominieren Lymnaea, Succinea und Gyraulus. Die Charophyten werden durch Chara globularis vertreten. Die paläoökologische Interpretation basiert auf den charakteristischen Faunen- und Florenelementen und auf der Natur der Sedimente. Es wird vermutet, daß der See während seiner ganzen Existenz ziemlich flach war und kaltes, extrem salzarmes, langsam fließendes, pflanzenreiches Wasser führte. Als ein offenes Becken mag er einen kontinuierlichen Abfluß während seiner ganzen Existenz gehabt haben. Die Entleerung des Sees wurde verursacht durch eine strukturelle Zerrüttung des Seebodens und die Ausfüllung durch riesige, durch einen weiteren Impuls tektonischer Aktivität ausgelöste Schuttmassen.

Description: Using detailed field evidence provided by trimlines on former nunataks, erratic boulders and the orientations of glacial striae, the surface geometry in the accumulation area during the Last Glacial Maximum was reconstructed for the area of SE Switzerland and adjacent Italy. Collectively, the trends of trimline elevations, flowlines deduced from glacial striae and bedrock morphology along the longitudinal valleys and their tributaries indicate that the former accumulation area consisted of an ice dome with the ice divide located over the area enclosed by Schlarignia, Cinuos-chel, Livigno and Piz Bernina. It attained a minimum altitude of approximately 3000 m. Modelling the topography of the ice surface using a Geographical Information System (GIS) is consistent with these results. The paleoclimatological signal included in this surface geometry was used to draw conclusions about the main atmospheric paleocireulation patterns and to outline the principal precipitation areas for the Alps during the last glaciation. It followed from this that ice build-up was principally related to dominating precipitation by southerly circulation (foehn). The prevaleance of foehn circulation most likely reflects a southward shift of the North Atlantic polar atmospheric front and of the accompanied storm track due to the advancing margin of sea ice. There exists good agreement between these assumptions and (a) results of global circulation models for the time of the LGM; (b) estimations of basal shear stress values and flow velocities for Ice Age glaciers; and (c) interpretations of paleowind indicators.

Description: The original tunnel valley theory was put forward by Ussing 1907. Its validity has, however, been doubted by most German geologists since then, especially because many so-called tunnel valleys are surprisingly wide (1 km or more). It was claimed that so wide tunnels or cavities under the ice were impossible. Since 1950, progress in glaciology (especially Nye 1952 and Shreve 1972) has caused a revival of the tunnel valley concept. Long and narrow ice tongues which have been postulated for North Germany by some researchers, according to Nye are only possible in mountainous terrain. On the other hand, Shreve's picture of the subgla-cial stream pattern matches precisely the known pattern of eskers and valley incisions in Denmark, Holstein, and Mecklenburg. Küster & Meyer (1979) and Ehlers & Linke (1989) interpret the buried valley incisions in northern Germany as eroded by subglacial streams. Until now, however, their large width has not been sufficiently explained. A group of Danish scientists including Ole Humlum has discussed this problem. A successive origin of the valleys appears to be most probable: during the winter with its reduced meltwater flow, the tunnel is narrowed by ice pressure. Therefore, it cannot carry the vastly increased amount of water during the spring, and a new tunnel has to be eroded, presumably partly into the substratum. Annual repetition of this process causes wide valley bottoms, only small parts of which were ever water-filled at any given time. It is shown that the morphology of the Danish tunnel valleys can be explained in every detail by such a sequence of events, and that no alternative theory can offer an equally satisfactory explanation.