The aquatic macrophytes of an English lowland river system: assessing response to nutrient enrichment

Assessment of the effects of nutrients in running water upon macrophytes is compounded by the variety of additional environmental factors which influence their growth. Some classification schemes have been effective in detecting eutrophication on a national or regional scale, and also downstream changes in large single catchments. However, in lowland rivers with naturally nutrient-rich geologies, detection of change at smaller spatial scales has been difficult. This study examined the macrophyte community at 44 sites on the river Welland, a small lowland catchment rising below 150 m in Leicestershire, England. The community at 23 of these sites was adequate for further analysis. The data show that the dearest effect on community composition is caused by watercourse size. However, sites below sewage works, even small village works, did show a reduction in Mean Trophic Rank, (MTR - an assesment system introduced into the UK over the last three years using a 10-100 scale based upon scores and cover value of indicator species). Overall there was a slight but significant correlation of MTR with soluble phosphate and nitrate. The effectiveness of the MTR method is limited at full catchment scale by low numbers of the indicator taxa at small upstream sites. Catchment-scale assessment of the plant community is probably best served by more detailed phytosociological analysis and by the further development of the 'habitat templet' approach.