ALBERT

Notes: The magnetometric resistivity (MMR) method uses a sensitive magnetometer to measure the low-level, low-frequency magnetic fields associated with the galvanic current flow between a pair of electrodes. While the MMR anomalies of simple structures such as dikes and vertical contacts have been determined analytically, there is a lack of systematic information on the expected responses from simple three-dimensional bodies. We determine the characteristic anomalies associated with square, plate-like conductors, which are excellent models of many base metal mineral deposits.The anomalies of plates of finite size are determined numerically using an integral equation method. A plate is subdivided into many sections and the current flow within each section is solved by equating the electrical field within each section to the tangential electrical field just outside it. When the plate size is small in relation to either the depth or the transmitter spacing, the shape and amplitude of the anomaly produced is closely approximated by a current dipole model of the same length and depth. At the other extreme, a large plate is represented by a half-plane. The dipole and half-plane models are used to bracket the behaviour of plates of finite size.The form of a plate anomaly is principally dependent on the shape, depth and orientation of the plate. A large, dipping plate near the surface produces a skewed anomaly highly indicative of its dip, but the amount of skew rapidly diminishes with increased depth or decreased size. Changes in plate conductivity affect the amplitude of the anomaly, but have little effect on anomaly shape. A current channelling parameter, determined from the conductivity contrast, can thus be used to scale the amplitude of an anomaly whose basic shape has been determined from geometrical considerations.The separation into geometrical and electrical factors greatly simplifies both the interpretation and modelling of MMR anomalies, particularly in situations with multiple plates. An empirical formula, using this separation, predicts the anomaly of two or more parallel plates with different conductances. In addition, the relation between the resolution of two vertical, parallel plates of equal conductance and their separation is determined.The ability of the integral equation method to model plate-like structures is demonstrated with the interpretation of an MMR anomaly in a survey conducted at Cork Tree Well in Western Australia. The buried conductor, a mineralized graphitic zone, is modelled with a vertical, bent plate. The depth to the top of the plate, and the plate conductance, is adjusted to fit the anomaly amplitude as closely as possible. From the modelling it would appear that this zone is not solely responsible for the observed anomaly.

Notes: SUMMARY. 1. Macroinvertebrates were sampled from three habitats at forty-five sites in the catchment of the Welsh River Wye. Species assemblages were ordinated by DECORANA. classified by TWIN-SPAN and related to physico-chemical factors using correlation and multiple discriminant analysis respectively.2. DECORANA axis 1 was correlated with pH or total hardness, whilst axis 2 correlated with slope or distance from source. TWINSPAN groupings were also related to hardness and, to a lesser extent, slope. Assemblages at soft-water sites (〈15gm−3 CaCO3) were composed mostly of Plecoptera but at hard-water sites, even at high slope (〉10 m km−1), the fauna was dominated numerically by Ephemerop-tera, net-spinning Trichoptera, Mollusca and Crustacea.3. We suggest that our data do not support the River Continuum Concept unless there are modifications to allow for multiple gradients.

Notes: SUMMARY. 1. A soft-water stream iti upland Wales was dosed with sulphuric acid and aluminiutn sulphate at two successive points to create sitnultaneous episodes of low pH, and low pH with increased aluminiutn. Chemical atid biological responses were measured before, during and after the episode and were compared with a reference zone.2. The pH fell frotn ∼7.0 to 4.28 (±0.18 SD) and 5.02 (±0.10) respectively in the acid and aluminium zones. Corresponding aluminium concentrations during the episode were 0.052 g Al m−3 (±0.008) and 0.347 g Al nr3 (±0.047), the former not differing significantly from the reference zone. The concentration of cadmium rose to 0.002- 0.011 g Cd m−3in both treated areas, but the concentrations of other metals were unchanged.3. In situ toxicity tests were performed with macroinvertebrates and fish. Chironomus riparius. Hydropsyche angustipennis and Dinocras cephalotes suffered no mortality. Ecdyonurus venosus, Baetis rhodani and Gammarus pulex showed up to 25% mortality in both treatment zones and further mortalities occurred after the episode. Brown trout Salmo trutta and salmon Valmo salar s howed 7–10% mortality in the acid zone, but 50–87% in the aluminium zone, where salmon had a significantly shorter LT50than trout.4. The drift of Simuliidae increased during treatment in both acid and aluminium zones. Drift densities of Dixa puherula, Protonemura meyeri, Ephemeralla ignita and Dicranota sp. increased in the aluminium zone. The most pronounced response was by Baetis rhodani in the aluminium zone where drift density increased by ×8.4 during the episode.5. Baetis rhodani was the only taxon to show a significant decline in benthic density during the treatment, and then only in the aluminium zone. Drift could account for most of the losses.6. The depth distribution of invertebrates in the substratum differed between zones following treatment. More individuals were present at the surface of the reference zone (1287 m−2±747) than at the surface of the other zones (〈400 m−2); however, densities at greater depths were similar. These patterns probably reflected differences prior to the treatments.

Notes: SUMMARY. 1. Single-station diel oxygen curves were used to monitor the oxygen metabolism of the Ogeechee River, a sixth-order blackwater river in the Coastal Plain of southeastern U.S.A., over a period of 4 years. Ecosystem production (P) and respiration (R) were estimated, and P/R ratios calculated to determine the extent of autotrophy characteristic of this type of river. The potential error in oxygen metabolism caused by photo-oxidation of dissolved organic carbon (DOC) in the water was measured and found to be minor.2. Rates of ecosystem primary production measured were intermediate compared to other rivers, ranging from 0.49 to 13.99g O2m−2 day −1.Primary production rates were highest during the summer when water levels were low. Regression analysis indicated that water depth and light absorption by DOM were significant predictors of primary production in this river. Incident light intensities were not significantly correlated with production rate.3. Respiration rates were unusually high, varying between 3.70 and 11.5 g O2 m−2 day − 1. System respiration also varied seasonally, but less than primary production. Rates were slightly higher in spring and summer.4. With one exception, P/R ratios were considerably lower than l throughout the study period, indicating that the Ogeechee River was highly heterotrophic. PIR ratios ranged from 0.09 to 1.3, and averaged 0.25.5. A carbon budget calculated for this river showed floodplain inputs were 7 times autochthonous production. Organic carbon turnover length was 690 km, considerably longer than has been reported for lower-order rivers.

Notes: Alfalfa juice, a highly proteinaceous liquid, was heated in steamfilled shell and tube and rotating coil heat exchangers to effect protein coagulation. The juice could be preheated prior to entering the heat exchanger by use of a recycle system. Lower fouling rates were obtained when the protein was denatured prior to contacting the exchanger surfaces and when the rotating coil exchanger was used. Chemical cleaning treatments could restore the heat transfer coefficient of a fouled exchanger to the original value.

Notes: Growth, size composition, condition factor and gonad index of the oil sardine, Sardinella longiceps Val., oscillated over an annual cycle in relation to upwelling. Growth in length was modelled using the formula of Pauly & Gaschütz (1979):〈displayedItem type="mathematics" xml:id="mu1" numbered="no"〉〈mediaResource alt="image" href="urn:x-wiley:00221112:JFB67:JFB_67_mu1"/〉where Lt= length cm at age t years, L∞= 23.8cm, K=0.97, to=0.70, C=1.08 and ts=−0.08. The relationship of growth rate, spawning, and condition factor, to upwelling and plankton blooms is discussed.

Notes: Tropical fish were collected by trawling in Yemeni waters. Age determinations were made on sections of vertebrae which were cross checked with scales. The values for the von Bertalanffy growth constants K were in the range 0.08–0.31. Total mortalities (Z) calculated from age compositions were in the range 0.31 to 0.67 for 11 species. The mean of 0.46 agreed closely with that derived from the formula of Pauly (1980a) of 0.45. Since the former included fishing mortality (F) in addition to natural mortality (M) it was suggested that a lower value be used in the Gulland (1968) yield formula: Y = 0.5 M Bo. Recruitment to the fishery for most species occurred by 3 years of age. The demersal fish stocks in Yemeni waters may not exceed 109×103 tonnes at the present time. Using a value for M of 0.3, the annual sustainable yield may be in the region of 16×103 tonnes.