Showing papers by "Chris Soulsby published in 2003"

Survival of salmonid eggs in a degraded gravel‐bed stream: effects of groundwater–surface water interactions

Abstract: The effect of hyporheic water quality on developing salmonids was assessed between spawning and hatch. Results from a low-lying degraded agricultural catchment (Newmills Burn) were compared with those from a near-pristine upland spawning stream (Girnock Burn), providing a set of comparisons beyond the range of hyporheic conditions present in the Newmills Burn. It was demonstrated that hyporheic water quality in the Newmills Burn varied temporally and spatially as a consequence of variable fluxes of chemically reduced groundwater through heterogeneous drift deposits. Mortality rates from samplers located within artificial redds ranged from 0 to 100% and showed a clear negative relationship with mean dissolved oxygen (DO) concentrations (r2 = 0.85, P < 0.01). Where embryo mortality was less than 100%, low DO appeared to affect rates of embryo development. Embryos exposed to lower DO concentrations were observed to have a higher percentage mass of yolk sac than those developing in more favourable conditions. The chemical characteristics of hyporheic water in the stream were indicative of the mixing of longer residence regional groundwater with local surface water at shallow depths. The hyporheic water of the Girnock Burn approximated closely to that of surface water suggesting a local origin. Hyporheic water quality affects egg survival and may limit recruitment when egg deposition is marginal or inadequate. A consideration of hyporheic dynamics and groundwater–stream interactions should form part of channel modification or restoration works in salmonid spawning streams. Copyright © 2003 John Wiley & Sons, Ltd.

Heterogeneity in ground water–surface water interactions in the hyporheic zone of a salmonid spawning stream

Abstract: 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.

A tracer‐based assessment of hydrological pathways at different spatial scales in a mesoscale Scottish catchment

Abstract: Geochemically based hydrograph separation techniques were used in a preliminary assessment to infer how runoff processes change with landscape characteristics and spatial scale (1–233 km2) within a mesoscale catchment in upland Scotland. A two-component end-member mixing analysis (EMMA) used Gran alkalinity as an assumed conservative tracer. Analysis indicated that, at all scales investigated, acidic overland flow and shallow subsurface storm flows from the peaty soils covering the catchment headwaters dominated storm runoff generation. The estimated groundwater contribution to annual runoff varied from 30% in the smallest (ca 1 km2) peat-dominated headwater catchment with limited groundwater storage, to >60% in larger catchments (>30 km2) with greater coverage of more freely draining soils and more extensive aquifers in alluvium and other drift. This simple approach offers a useful, integrated conceptualization of the hydrological functioning in a mesoscale catchment, which can be tested and further refined by focused modelling and process-based research. However, even as it stands, the simple conceptualization of system behaviour will have significant utility as a tool for communicating hydrological issues in a range of planning and management decisions. Copyright © 2002 John Wiley & Sons, Ltd.

Groundwater-surface water interactions in a braided river: a tracer-based assessment.

Abstract: Natural tracers (alkalinity and silica) were used to infer groundwater–surface-water exchanges in the main braided reach of the River Feshie, Cairngorms, Scotland. Stream-water samples were collected upstream and downstream of the braided section at fortnightly intervals throughout the 2001–2002 hydrological year and subsequently at finer resolution over two rainfall events. The braided reach was found to exert a significant downstream buffering effect on the alkalinity of these waters, particularly at moderate flows (4–8 m3 s−1/≅Q30–70). Extensive hydrochemical surveys were undertaken to characterize the different source waters feeding the braids. Shallow groundwater flow systems at the edge of the braided floodplain, recharged by effluent streams and hillslope drainage, appeared to be of particular significance. Deeper groundwater was identified closer to the main channel, upwelling through the hyporheic zone. Both sources contributed to the significant groundwater–surface-water interactions that promote the buffering effect observed through the braided reach. Their impact was less significant at higher flows (>15 m3 s−1/>Q10) when acidic storm runoff from the peat-covered catchment headwaters dominated, as well as under baseflow conditions (<4 m3 s−1/

Towards integrating tracer studies in conceptual rainfall-runoff models: recent insights from a sub-arctic catchment in the Cairngorm Mountains, Scotland

Abstract: Hydrochemical tracers (alkalinity and silica) were used in an end-member mixing analysis (EMMA) of runoff sources in the 10 km 2 Allt a' Mharcaidh catchment. A three-component mixing model was used to separate the hydrograph and estimate, to a first approximation, the range of likely contributions of overland flow, shallow subsurface storm flow, and groundwater to the annual hydrograph. A conceptual, catchment-scale rainfall-runoff model (DIY) was also used to separate the annual hydrograph in an equivalent set of flow paths. The two approaches produced independent representations of catchment hydrology that exhibited reasonable agreement. This showed the dominance of overland flow in generating storm runoff and the important role of groundwater inputs throughout the hydrological year. Moreover, DIY was successfully adapted to simulate stream chemistry (alkalinity) at daily time steps. Sensitivity analysis showed that whilst a distinct groundwater source at the catchment scale could be identified, there was considerable uncertainty in differentiating between overland flow and subsurface storm flow in both the EMMA and DIY applications. Nevertheless, the study indicated that the complementary use of tracer analysis in EMMA can increase the confidence in conceptual model structure. However, conclusions are restricted to the specific spatial and temporal scales examined.

Parameter identification for conceptual modelling using combined behavioural knowledge

Abstract: Improved methods for identification of conceptual parameter values are necessary if hydrological models are to be applied to catchments other than those to which they have been specifically calibrated. A technique has been devised to calculate conceptual parameter sets of a semi-distributed hydrological model using a soil hydrological classification in addition to topographic data. The method is tested in this paper by converting multiple parameter sets, calibrated to two separate catchments, into parameter sets for a third catchment. The prediction capabilities of the parameter sets are studied for the new catchment in terms of both simulation of total streamflow and the separation of that flow into three components, corresponding to groundwater recharge, sub. surface flow, and surface runoff. The results from an end-member mixing analysis (EMMA) using geochemical tracers are employed to assess the flow separation. Results from the simulations demonstrate that there is quite wide variability in the success of the parameter sets at predicting streamflow for the new catchment. There is also considerable variation in the predicted stream flow separation, with only 28 out of 500 simulations giving a comparable result to the EMMA. By accepting or rejecting simulations using these results, the EMMA can be used to reduce the structural uncertainty of the model. However, it does not help to reduce constraints on acceptable parameter values for the simulations, and further research is still necessary to improve parameter identifiability.