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 influe nce their growth. Some classification schemes have been effective in detect ing eutrophication on a national or regional scale, and also downstream cha nges 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 Leicest ershire, England. The community at 23 of these sites was adequate for furth er analysis. The data show that the dearest effect on community composition is caused by watercourse size. However, sites below sewage works, even sma ll village works, did show a reduction in Mean Trophic Rank, (MTR - an asse sment system introduced into the UK over the last three years using a 10-10 0 scale based upon scores and cover value of indicator species). Overall th ere was a slight but significant correlation of MTR with soluble phosphate and nitrate. The effectiveness of the MTR method is limited at full catchme nt scale by low numbers of the indicator taxa at small upstream sites. Catc hment-scale assessment of the plant community is probably best served by mo re detailed phytosociological analysis and by the further development of th e 'habitat templet' approach.