Scales of hydroecological variability within a groundwater-dominated stream

This paper aims to show how hydrological, ecological and climatological data may be analysed to assess the temporal and spatial scales at which hydroclimatological variables influence instream ecology. A groundwater-dominated chalk stream (Little Stour River, Kent, UK), for which ecological data are available over 6 years (1992–1997), provides the focus for the testing and application of these techniques. Correlation and regression analyses are undertaken to highlight the dominant hydroclimatological factors influencing community abundance at a range of spatial scales encompassing: the entire river, upstream and downstream sectors, habitat type (riffle) and individual riffle sites. To set these results in a longer-term context, temporal sequencing of annual air temperature and discharge regimes is undertaken (based upon 30 years of data, 1969–1999). A classification of annual discharge hydrograph ‘shape’ and ‘magnitude’ identifies years with early, intermediate or late peaks, which may be assigned into three magnitude groups. Four annual air temperature ‘magnitude’ classes are apparent. The regime analysis clearly reveals inter-annual variability in both these key physical habitat parameters. Analysis of variance indicates a significant difference in macroinvertebrate community abundance for the hydrograph ‘shape’, ‘magnitude’ and combined classes identified at all scales of analysis, although the influence of air temperature only varied significantly between riffle sites. The techniques used may be easily adapted to water resource management.