Impacts of agricultural land-use practices upon in-stream ecological structure and processes.

Abstract

Phosphorus loss in run-off and drainage from agricultural land has been linked to eutrophication problems in a number of freshwaters. Many farming systems and land management practices have been indicated as those most likely to lead to high phosphorus losses at field and farm scale. However, it is unclear exactly what level of phosphorus loss is necessary to cause a significant eutrophication response in receiving streams, or the speed with which the response occurs.
The objective of this research is to quantify the influence of phosphorus concentration on the ecology of the lowland streams by measuring changes in structure of macroinvertebrate and diatom communities and by measuring changes in ecological processes. The stream waters of three paired headwater catchments in lowland England and Wales, which are characteristic of selected livestock and farming systems with variable P-loss risk, provide a gradient of phosphorus concentrations from limits of detection to highly eutrophic (median concentrations for all data collected ranging from 10 to 240 µg-SRP/L and from 22 to 334 µg-TP/L). Ecological structure and processes were measured in comparable meso-habitats (functional habitats) at each site to minimise physical differences. Invertebrate community composition and diatom species diversity with chlorophyll 'a' biomass were the structural measurements; photosynthesis, respiration, phosphatase activity and leaf decomposition the functional measurements.