The effects of agricultural land use on the community structure and functioning of small freshwater habitats

Agriculture is important for maintaining human well-being, but intensive agricultural production can have adverse environmental impacts. Freshwater ecosystems are particularly vulnerable to chemical and physical stressors resulting from agricultural land use, but few studies have compared the effects of different types of agricultural practices on the ecology of small water bodies. In agricultural catchments, the two major land uses, arable and pastoral, differ in their management (e.g. ploughing, fertilizer and pesticide inputs) and therefore in their potential effect on freshwater communities. The aim of this study was to investigate the effects of two types of agricultural land use (arable and pastoral) on the community structure and functioning of ponds and streams. Twenty four sites (6 arable ponds, 6 arable streams, 6 pastoral ponds and 6 pastoral streams) were studied in Leicestershire, UK. Arable streams had lower macroinvertebrate abundance and taxonomic richness than pastoral streams and arable ponds had lower diatom species richness, diversity and evenness than pastoral ponds. Leaf litter decomposition was also higher in arable than pastoral ponds. Feeding by macroinvertebrate shredders (e.g. Gammarus pulex) was a significant contributor to leaf breakdown in streams but not in ponds. The feeding rates of G. pulex and Asellus aquaticus were significantly affected by temperature and intraspecific interactions (i.e. density). Increasing density resulted in greater per capita leaf mass loss of A. aquaticus and lower survival rate of G. pulex. At higher temperature, the per capita leaf mass loss and feeding rates for both species were greater whereas the survival rates were lower. Agricultural land use can adversely affect the structure and functioning of aquatic communities. Consequently, it may have a considerable potential impact on ecosystem services provided by freshwater habitats. Understanding the possible effects of agricultural land use on the structure and functioning of freshwater ecosystems is extremely important and should help in identifying the best land use management to maintain sustainable agricultural production and protect freshwater habitats.