Groundwater in headwaters: hydrological and ecological significance

Abstract

The hydrological and ecological significance of groundwater has generally been under-estimated in headwater catchment studies within the Celtic regions. The paper presents data from headwater catchments in both upland and lowland settings in northern Scotland to address this gap in our understanding. Research in the 10 km2 Allt a’ Mharcaidh catchment in the western Cairngorms has demonstrated that a range of groundwater sources in various drift deposits can account for c. 50% of annual runoff, even in a high altitude headwater stream. Despite the traditional assumption that upland catchments have limited aquifer storage, oxygen isotope studies of groundwater imply mean water residence times of up to five years which indicate a range of groundwater sources in montane environments. Moreover, hydrogeochemical reactions in the saturated zone appear to regulate stream water chemistry at moderate and low flows. In such montane environments, groundwater discharges at springs create unique wetland habitats which often form the source of headwater streams and affect riparian areas. In lowland catchments the hydrological significance of groundwater is equally important. In addition, recent studies in a salmon spawning stream in the Newmills Burn, Aberdeenshire has shown that aquifer-stream interactions in hyporheic zones are crucial in maintaining habitat conditions conducive to the survival of salmonid eggs, and the subsequent population of salmon streams. It is concluded that interdisciplinary studies incorporating hydrogeological investigations are fundamental to a proper understanding of the hydrology and functional ecology of catchment systems in the Celtic regions.

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

“…This approach underlines an ecological relevance of traditional hillslope hydrology that has not been emphasized sufficiently in previous studies of streams (Soulsby et al, 2000a). In this paper we highlight the importance of spatial and temporal heterogeneity in ground water-surface water interactions in a lowland gravel-bed stream in Scotland that is intensively used by spawning salmonids.…”

A field‐based assessment of oxygen supply to incubating Atlantic salmon (Salmo salar) embryos

“…Survival was typically restricted to the top layer of eggs within each Harris basket, and the results of a two-sample t-test (95% confidence limit) indicated a significant difference in survival between the top and lower egg layers. The supposition that oxygen availability declines with depth is supported by studies of oxygen concentration and interstitial flow velocity within riverbeds (Whitman and Clark, 1982;Malard and Hervant, 1999;Soulsby et al, 2000;Malcolm et al, 2003). In additional to vertical variations in incubation conditions, differences in survival and interstitial oxygen availability were recorded between egg locations within an individual redd.…”

“…The purpose of this analysis is to highlight the application of information pertaining to oxygen availability as a means of identifying potential causes of oxygen-limiting conditions. Studies investigating the hyporheic zone and salmonid incubation gravels indicate that the flux of oxygen through spawning gravels is dependent on a complex interaction of surface and subsurface factors (Soulsby et al, 2000;Malcolm et al, 2003;Greig et al, 2005cGreig et al, , 2007. In summary, sediment accumulation within the riverbed blocks interstitial pore spaces and inhibits the passage of oxygenated water (Chapman, 1988;Bjorn and Reiser, 1991).…”

“…Oxygen demands, which develop when oxygen-consuming 3088 S. GREIG, D. SEAR AND P. CARLING material accumulates in the riverbed, remove oxygen from interstitial water, thereby lowering interstitial oxygen concentrations (Whitman and Clark, 1982;Chevalier and Carson, 1985;Štěrba et al, 1992). Groundwater, which seeps into the riverbed from subsurface storage zones, imparts a spatially and temporally variable influence on interstitial oxygen concentrations (Sheridan, 1962;Soulsby et al, 2000;Soulsby and Malcolm, 2001;Malcolm et al, 2003). Finally, pressure and turbulencedriven surface-subsurface exchange processes influence the depth of penetration and flux of surface water into and through the riverbed (Vaux, 1968;Savant et al, 1987;Shimizu et al, 1990;Mendoza and Zhou, 1992;Harvey and Bencala, 1993).…”

An overview of groundwater in Scotland

“…Groundwater sustains river flows throughout the year and even in small upland streams may account for 30% of the flow, invaluable for sustaining Salmon populations (Soulsby et al 2000) and keeping streams and rivers viable over dry summers. In addition, groundwater has an important role in sustaining wetlands and fragile Submitted version 2005 ecologies, such as parts of the machair.…”