Showing papers by "Chris Soulsby published in 2001"

Hydrochemistry of the hyporheic zone in salmon spawning gravels: a preliminary assessment in a degraded agricultural stream

Abstract: Hydrochemical changes were monitored in a simulated, sea run salmon redd in a small agricultural stream in northeast Scotland following the 1998–1999 spawning season. Immediately after redd construction, the hydrochemical characteristics of hyporheic water, at depths of 0.1 m and 0.3 m, were very similar to stream water. These apparently well-mixed waters were alkaline, well-oxygenated and enriched in nutrients. In the weeks and months following redd construction, clear and statistically significant differences in the chemistry of stream and hyporheic waters were observed. Typically, hyporheic water had lower concentrations of dissolved oxygen (mean 7.35 mg L−1 at 0.3 m depth) than stream waters (mean=11.26 mg L−1). Alkalinity, calcium, sulphate and conductivity levels tended to be higher in hyporheic waters, with concentrations increasing with depth. These data implied an increasing influence of groundwater with depth in the hyporheic zone following redd construction; an inference supported by subsequent hydraulic head measurements, which revealed an upwards groundwater flux in the stream bed. However, groundwater–surface water interactions were dynamic and complex: road salts eluted into the stream during periods of snowmelt simulated tracer experiments that implied that a reversed hydraulic gradient may occur at high flows with deeper streamwater penetration and mixing in the hyporheic zone. High flows also result in the mobilization of fine sediments from the stream bed which subsequently infiltrated into spawning gravels. These appear to cause ‘capping’ of redds and probably reduce the hydraulic conductivity of the redd matrix. Infiltrating sediments also contain a small, but probably important organic component, the decomposition of which may contribute to oxygen consumption and nutrient mineralization in the hyporheic zone. Copyright © 2001 John Wiley & Sons, Ltd.

Invertebrate communities and hydrological variation in Cairngorm mountain streams

Abstract: Macroinvertebrates, discharge and 16 chemical variables were monitored over a 14-year period in four small streams (catchment area <15 km2) in the Cairngorm mountains, Scotland. Canonical Correspondence Analysis (CCA) was used to assess relationships between invertebrates and environmental conditions on the day of sampling, average conditions over the preceding 1, 2 and 3-month periods and indices of hydrological and hydrochemical variation over preceding monthly intervals. CCA detected subtle inter-catchment differences in invertebrate community structure, with catchments separated along axes representing streamwater calcium, alkalinity and total organic carbon concentrations. Invertebrate communities varied seasonally, with spring, summer and autumn samples separated along CCA axes representing temperature, orthosilicate and discharge. Hydrochemically, spring was the most variable season, characterised by increased frequency of both high and low flow events and acid, snowmelt episodes. In two of the streams, invertebrate community structure varied more in spring than in other seasons. CCA ordinations using indices of hydrological and hydrochemical variation over preceding time periods were more successful (increased eigenvalues) at explaining temporal variation in invertebrate community structure than those using conditions on the day of sampling or average conditions over preceding time periods. For one of the catchments, 40% of the seasonal and between-year variation over the 14-year period could be explained by the frequency of high and low flow events, maximum and minimum water temperatures and acid episodes in the two months prior to the invertebrate samples being collected. The single most important flow parameter (longest CCA arrow) was the frequency of high flow events greater than three times the median discharge. No significant trends in invertebrate community composition were found in any of the streams over the 14-year period so, despite the apparent importance of hydrological and hydrochemical variation, communities appeared stable over the long-term.

Seasonality, water quality trends and biological responses in four streams in the Cairngorm Mountains, Scotland

Abstract: . The chemical composition and invertebrate communities found in four streams in the Cairngorms, Scotland, were monitored between 1985-1997. Stream waters were mildly acidic (mean pH ca. 6.5), with low alkalinity (mean acid neutralising capacity varying from 35-117 meq l-1) and low ionic strength. Subtle differences in the chemistry of each stream were reflected in their invertebrate faunas. Strong seasonality in water chemistry occurred, with the most acid, low alkalinity waters observed during the winter and early spring. This was particularly marked during snowmelt between January and April. In contrast, summer flows were usually groundwater dominated and characterised by higher alkalinity and higher concentrations of most other weathering-derived solutes. Seasonality was also clear in the invertebrate data, with Canonical Correspondence Analysis (CCA) separating seasonal samples along axes related to water temperature and discharge characteristics. Inter-annual hydrological and chemical differences were marked, particularly with respect to the winter period. Invertebrate communities found in each of the streams also varied from year to year, with spring communities significantly more variable (P Hydrochemical trends over the study period were analysed using a seasonal Kendall test, LOcally WEighted Scatterplot Smoothing (LOWESS) and graphical techniques. These indicated that a reduction in sulphate concentrations in stream water is occurring, consistent with declining levels of atmospheric deposition. This may be matched by increases in pH and declining calcium concentrations, though available evidence is inconclusive. Other parameters, such as chloride, total organic carbon and zinc, reveal somewhat random patterns, probably reflecting irregular variations in climatic factors and/or atmospheric deposition. Previous studies have shown that the stream invertebrate communities have remained stable over this period (i.e. no significant linear trends) and show no evidence of acid-related impoverishment. Thus, over longer timescales invertebrates in these streams appear robust to the short-term (seasonal and inter-annual) environmental variability and long-term (decadal) chemical changes identified. Keywords: hydrochemistry, hydrology, trends, macroinvertebrates, uplands, Cairngorms, acidification

Developing ecologically acceptable river flow regimes: a case study of Kielder reservoir and the Kielder water transfer system

Abstract: Kielder Reservoir and the Kielder water transfer scheme have been operational since the early 1980s. The hydro-ecological changes that occur in the River North Tyne and the River Wear as a result of Kielder operations are highlighted and release policy changes designed to minimize impacts on salmonid fish are described. The Kielder Reservoir release regime results in sudden and marked changes in flow in the North Tyne. These changes affect the availability of suitable habitat for newly emerged 0+ Atlantic salmon Salmo salar L. and potentially lead to the drying out of areas used for spawning. Physical Habitat Simulation (PHABSIM) models suggest that the reservoir compensation flow provides adequate habitat for older 0+ fish but limits the availability of spawning habitat. A seasonally variable compensation and hydroelectric power (HEP) release regime that limits impacts and increases suitable spawning and 0+ habitat is described. Transfers of water to the River Wear result in short-term changes in the abundance of certain invertebrate species, although there is no evidence that the river’s invertebrate fauna has been permanently altered. Consequently, it is unlikely that fish are affected indirectly by transfers through reductions in the abundance of their invertebrate prey. Transfers allow abstractions for potable and industrial water supply to continue without breaching the river’s statutory Minimum Maintained Flow (MMF). The PHABSIM models suggest that this augmentation helps avoid the loss of salmonid habitat during summer dry periods. Simulation of the impacts of some alternative regimes indicates that salmonid habitat could be increased further but at the expense of natural flow and habitat variation. Research findings do not suggest the need for changes to the transfer release regime.

Flow Requirements of Spawning Atlantic Salmon in an Upland Stream: Implications for Water‐Resource Management

Abstract: The spawning sites selected by female Atlantic salmon (Salmo salar) were surveyed over three consecutive years in the Girnock Burn, Aberdeenshire, Scotland. Discharge was calculated for each spawning site to assess within-catchment variation in spawning discharge selection. In total, 428 incidents of female spawning activity were logged at 48 sites. Fish selected relatively high flows in which to spawn, with the lowest utilised discharge being equivalent to the burn's 50 percentile flow. The results emphasise the importance of relatively high flows during the spawning season and, more specifically, a range of flows which ensures that sites are distributed as widely as possible and are accessible and suitable.