Scale‐dependent effects of fine sediments on temperate headwater invertebrates
Tóm tắt
1. Anthropogenic activities can increase fine sediment supply to streams over multiple spatial and temporal extents. Identifying the processes responsible, and the scale at which any effects on stream organisms become evident, are key management needs, but appropriately scaled surveys are surprisingly few.
2. We surveyed macroinvertebrates and superficial fine sediments at two spatial resolutions (reach‐ and patch‐scale) in tributaries of the River Usk, a temperate, montane catchment in rural Wales (U.K.). Land use, habitat and geomorphological character were measured on‐site or derived from an existing database (=Fluvial Audit). We aimed to identify: (i) how in‐stream sediments varied with land use and associated geomorphology; (ii) likely consequences for macroinvertebrates and (iii) any scale‐dependence in relationships between macroinvertebrates and sediment character.
3. At both the reach‐ and patch‐scales, bed cover by fine sediment was related directly to the extent of eroding banks 500 m upstream. In turn, sedimentation and bank erosion were negatively correlated with catchment or riparian woodland extent.
4. At the reach scale, macroinvertebrate composition varied with catchment land use and stream chemistry, with richness declining as rough grazing or woodland was replaced by improved grassland. There was no response to deposited sediment except for weak increase in the relative abundance of oligochaetes.
5. By contrast, at the patch scale, fine sediments were accompanied by pronounced changes in invertebrate composition, and we ranked the 27 most common taxa according to their apparent sediment tolerance. General estimating equations showed that total and Ephemeroptera, Plecoptera and Trichoptera richness decreased significantly by 20% and 25% at the most sediment impacted sites (30% cover) by comparison with sediment‐free sites.
6. We conclude that sediment deposition in the upper Usk system mostly reflects local bank erosion, with riparian woodland likely to mediate this process through bank stability. Fine sediment release had marked ecological effects, but these were detectable only at patch‐to‐patch scales. We suggest that investigation of localized sediment release in streams will benefit from scale‐dependent or scale‐specific sampling, and some effects could go undetected unless sample resolution is selected carefully.
Từ khóa
Tài liệu tham khảo
Clews E., 2008, Improving bio‐diagnostic monitoring using simple combinations of standard biotic indices, River Research and Applications
Countryside Council for Wales, 2002, Phase 1 Survey From the Countryside Council for Wales
Dosskey M.G., 2007, Change in filter strip performance over ten years, Journal of Soil and Water Conservation, 62, 21
Edington J.M., 1981, A Key to the Caseless Caddis Larvae of the British Isles with Notes on their Ecology
Elliott J., 1988, Larvae of the British Ephemeroptera: A Key with Ecological Notes
Emery J.C., 2005, Fluvial Audit of the Upper Usk Tributaries
Environment Agency, 1998, Rural Usk LEAP Consultation Report
Environment Agency, 1999, Procedures for Collecting and Analysing Macroinvertebrate Samples. Quality Management Systems for Environmental Monitoring: Biological Techniques
Environment Agency, 2003, River Habitat Survey in Britain and Ireland, Field Survey Guidance Manual
ESRI, 2004, ArcGIS 9.1. E.S.R.I. Inc
Fossati O., 2001, Impact of sediment releases on water chemistry and mocroinvertebrate communities in clear water Andean stream (Bolivia), Archiv fur Hydrobiologie, 151, 33, 10.1127/archiv-hydrobiol/151/2001/33
Friday L., 1988, A Key to the Adults of British Water Beetles
Knighton D., 1998, Fluvial Forms and Processes: A New Perspective
Platts W.S., 1983, Mehods for Evaluating Stream, Riparian, and Biotic Conditions, 10.2737/INT-GTR-138
Standing Committee of Analysts, 1979, Dissolved Oxygen in Natural and Waste Waters
Standing Committee of Analysts, 1981, Biological Oxygen Demand
Standing Committee of Analysts, 1987, Kjeldahl Nitrogen in Waters
Standing Committee of Analysts, 1992, Phosphorus and Silicon in Waters, Effluents and Sludges
Wallace I., 2003, Keys to the Case‐Bearing Caddis Larvae of Britain and Ireland
Waters T.F., 1995, Sediments in Streams: Sources, Biological Effects, and Control