ALBERT

Description: Tracer investigations were combined with a geographical information system (GIS) analysis of the 31 km2 Girnock catchment (Cairngorm Mountains, Scotland) in order to understand hydrological functioning by identifying dominant runoff sources and estimating mean residence times. The catchment has a complex geology, soil cover and topography. Gran alkalinity was used to demonstrate that catchment geology has a dominant influence on baseflow chemistry, but flow paths originating in acidic horizons in the upper soil profiles controlled stormflow alkalinity. Chemically based hydrograph separations at the catchment scale indicated that ∼30% of annual runoff was derived from groundwater sources. Similar contributions (23-36%) were estimated for virtually all major sub-basins. δ18O of precipitation (mean: -9.4‰; range: -16.1 to -5.0‰) and stream waters (mean: -9.1‰; range: -11.6 to -7.4‰) were used to assess mean catchment and sub-basin residence times, which were in the order ∼4-6 months. GIS analysis showed that these tracer-based diagnostic features of catchment functioning were consistent with the landscape organization of the catchment. Soil and HOST (Hydrology of Soil Type) maps indicated that the catchment and individual sub-basins were dominated by hydrologically responsive soils, such as peats (Histosol), peaty gleys (Histic Gleysols) and tankers (Umbric Leptosols and Histosols). Soil cover (in combination with a topographic index) predicted extensive areas of saturation that probably expand during hydrological events, thus providing a high degree of hydrological connectivity between catchment hillslopes and stream channel network. This was validated by aerial photographic interpretation and groundtruthing. These characteristics of hydrological functioning (i.e. dominance of responsive hydrological pathways and short residence times) dictate that the catchment is sensitive to land use change impacts on the quality and quantity of streamflows. It is suggested that such conceptualization of hydrological functioning using tracer-validated GIS analysis can play an important role in the sustainable management of river basins. Copyright © 2006 John Wiley & Sons, Ltd.

Description: This study focuses on understanding the temporal variability in hydrological and thermal conditions in a small mountain stream and its potential implication for two life stages of Atlantic salmon (Salmo salar) – stream resident juveniles and returning adult spawners. Stream discharge and temperature in the Girnock Burn, NE Scotland, were characterised over ten hydrological years (1994/1995–2003/2004). Attention was focussed on assessing variations during particular ecologically "sensitive" time periods when selected life-stages of salmon behaviour may be especially influenced by hydrological and thermal conditions. Empirical discharge data were used to derive hydraulic parameters to predict the Critical Displacement Velocity (CDV) of juvenile salmon. This is the velocity above which fish may no longer be able to hold station in the water column and thus can be used as an index of time periods where feeding behaviour might be constrained. In the Girnock Burn, strong inter- and intra-annual variability in hydrological and thermal conditions may have important implications for feeding opportunities for juvenile fish; both during important growth periods in late winter and early spring, and the emergence of fry in the late spring. Time periods when foraging behaviour of juvenile salmon may be constrained by hydraulic conditions were assessed as the percentage time when CDV for 0+ and 1+ fish were exceeded by mean daily stream velocities. Clear seasonal patterns of CDV were apparent, with higher summer values driven by higher stream temperatures and fish length. Inter-annual variability in the time when mean stream velocity exceeded CDV for 0+ fish ranged between 29.3% (1997/1998) and 44.7% (2000/2001). For 1+ fish mean stream velocity exceeded CDV between 14.5% (1997/1998) and 30.7% (2000/2001) of the time. The movement of adult spawners into the Girnock Burn in preparation for autumn spawning (late October to mid-November) exhibited a complex relationship with hydrological variability with marked inter-annual contrasts. In years when discharge in the period prior to spawning was low, fish movement was increasingly triggered by suboptimal flow increases as spawning time approached. In contrast, wet years with numerous events allowed a much more even distribution of fish entry. Elucidating links between discharge/temperature variability and foraging opportunities and upriver migration of adult Atlantic salmon have the potential to contribute to the improvement of conservation strategies in both regulated and unregulated rivers.

Description: Spatial and temporal variability in ground water-surface water interactions in the hyporheic zone of a salmonid spawning stream was investigated. Four locations in a 150-m reach of the stream were studied using hydrometric and hydrochemical tracing techniques. A high degree of hydrological connectivity between the riparian hillslope and the stream channel was indicated at two locations, where hydrochemical changes and hydraulic gradients indicated that the hyporheic zone was dominated by upwelling ground water. The chemistry of ground water reflected relatively long residence times and reducing conditions with high levels of alkalinity and conductivity, low dissolved oxygen (DO) and nitrate. At the other locations, connectivity was less evident and, at most times, the hyporheic zone was dominated by downwelling stream water characterized by high DO, low alkalinity and conductivity. Substantial variability in hyporheic chemistry was evident at fine (〈 10 m) spatial scales and changed rapidly over the course of hydrological events. The nature of the hydrochemical response varied among locations depending on the strength of local ground water influence. It is suggested that greater emphasis on spatial and temporal heterogeneity in ground water-surface water interactions in the hyporheic zone is necessary for a consideration of hydrochemical effects on many aspects of stream ecology. For example, the survival of salmonid eggs in hyporheic gravels varied considerably among the locations studied and was shown to be associated with variation in interstitial chemistry. River restoration schemes and watershed management strategies based only on the surface expression of catchment characteristics risk excluding consideration of potentially critical subsurface processes. © 2002 John Wiley and Sons, Ltd.

Description: The spatial and temporal variability of groundwater-surface-water (GW-SW) interactions was investigated in an intensively utilized salmon spawning riffle. Hydrochemical tracers, were used along with high-resolution hydraulic head and temperature data to assess hyporheic dynamics. Surface and subsurface hydrochemistry were monitored at three locations where salmon spawning had been observed in previous years. Temperature and hydraulic head were monitored in three nests of three piezometers located to characterize the head, the run and the tail-out of the riffle feature. Hydrochemical gradients between surface and subsurface water indicated increasing GW influence with depth into the hyporheic zone. Surface water was characterized by high dissolved oxygen (DO) concentrations, low alkalinity and conductivity. Hyporheic water was generally characterized by high levels of alkalinity and conductivity indicative of longer residence times, and low DO, indicative of reducing conditions. Hydrochemical and temperature gradients varied spatially over the riffle in response to changes in local GW-SW interactions at the depths investigated. Groundwater inputs dominated the head and tail of the riffle. The influence of SW increased in the area of accelerating flow and decreasing water depth through the run of the riffle. Temporal GW-SW interactions also varied in response to changing hydrological conditions. Gross changes in hyporheic hydrochemistry were observed at the weekly scale in response to changing flow conditions and surface water inputs to the hyporheic zone. During low flows, caused by freezing or dry weather, hyporheic, hydrochemistry was dominated by GW inputs. During higher flows hyporheic hydrochemistry indicated that SW contributions increased. In addition, high-resolution hydraulic head data indicated that rapid changes in GW-SW interactions occurred during hydrological events. The spatial, and possibly the temporal, variability of GW-SW interactions had a marked effect on the survival of salmon ova. It is concluded that hyporheic dynamics and their effect on stream ecology should be given increased consideration by fisheries and water resource managers. © 2004 John Wiley and Sons, Ltd.

Description: The spatio-temporal variability of stream water temperatures was investigated at six locations on the Girnock Burn (30km2 catchment), Cairngorms, Scotland over three hydrological years between 1998 and 2002. The key site-specific factors affecting the hydrology and climatology of the sampling points were investigated as a basis for physical process inference. Particular emphasis was placed on assessing the effects of riparian forest in the lower catchment versus the heather moorland riparian zones that are spatially dominant in the upper catchment. The findings were related to river heat budget studies that provided process detail. Gross changes in stream temperature were affected by the annual cycle of incoming solar radiation and seasonal changes in hydrological and climatological conditions. Inter-annual variation in these controlling variables resulted in inter-annual variability in thermal regime. However, more subtle inter-site differences reflected the impact of site-specific characteristics on various components of the river energy budget. Inter-site variability was most apparent at shorter time scales, during the summer months and for higher stream temperatures. Riparian woodland in the lower catchment had a substantial impact on thermal regime, reducing diel variability (over a period of 24 hours) and temperature extremes. Observed inter-site differences are likely to have a substantial effect on freshwater ecology in general and salmonid fish in particular. Keywords: temperature, thermal regime, forest, salmon, hydrology, Girnock Burn, Cairngorm

Description: This paper presents a novel method for assessing hyporheic water quality dynamics using advances in sensor technology. High-resolution (15 min) dissolved oxygen (DO) and hydraulic head data were combined to assess groundwater-surface water (GW-SW) interactions in the hyporheic zone. DO concentrations varied at fine temporal and spatial scales, depending on the relative contributions of GW and SW. The effect of sample frequency on observed patterns of variability was assessed with reference to studies of the ecology of salmon spawning habitat. Conventional approaches fail to capture the full range of temporal variability in hyporheic water quality and demonstrate the need to reassess the interpretations of previous studies of the hyporheic zone. © Crown Copyright 2006. Reproduced with the permission of Her Majesty's Stationery Office. Published by John Wiley & Sons, Ltd.

Description: Stream temperature was monitored at five mainstem locations and one tributary location on the Gimock Burn, a 31-km2 tributary catchment of the Aberdeenshire Dee in north-east Scotland. Stream temperature was recorded at 15-min resolution between April 2003 and March 2006 to investigate the influence of semi-natural riparian woodland on the spatial and temporal variability of stream temperature and the influence that this had on the performance of juvenile Atlantic salmon (Salmo salar). Two upstream sites were located in open moorland locations, while three downstream sites were located in areas of mixed deciduous/ coniferous woodland areas at progressive distances of 0.75, 1.5 and 2.0 km from the upstream edge of continuous riparian tree cover. The effects of riparian woodland on stream temperature varied through the year, increasing during the spring to a maximum in summer, before decreasing once again in autumn. Maximum, mean and diel temperature amplitude were lower and minimum temperatures higher at woodland sites when compared to those located in open moorland. Although significant differences in fish performance were detected between sites, the influence of temperature variability was unclear due to confounding factors, some of which could not be measured during the study. It is recommended that future studies should combine advances in field-based temperature monitoring with those in hydroclimatology to develop realistic process-based models that can be used for stream temperature prediction. Further advances are needed in understanding the relationship between naturally variable thermal regime and fish performance in order that ecological predictions can be usefully made from field and modelled temperature data. © Crown Copyright 2008. Reproduced with the permission of Her Majesty's Stationery Office. Published by John Wiley & Sons, Ltd.