Land use effects on macroinvertebrate assemblages and stream quality along an agricultural river basin

The response of macroinvertebrate assemblages to pollution (agricultural and municipal) and river habitat modification (riparian and stream channel) resulting from land use changes was assessed alone, the longitudinal gradient of an agricultural river basin (Pamisos River, S. Greece). Five sampling sites were selected and benthic macroinvertebrates were sampled proportionally to microhabitat coverage of each site at the beginning of the dry season (June 2002) and at the end of the wet season (April 2003). Land use at local and catchment scale and physicochemical variables were recorded while River Habitat Survey (RHS) was performed to assess the hydromorphological condition of the sites. Overall, sites ranged from poor to moderate ecological quality, as classified according to the Water Framework Directive (2000/60/EC) scheme. Relationships between macroinvertebrate assemblages and environmental variables such as land use, hydrochemistry, microhabitat composition and hydromorphological degradation were examined using canonical ordination techniques (CCA). According to CCA, agricultural land, stream width, nitrate and parts of terrestrial plants were the most important variables structuring, macroinvertebrate assemblages. The combined effects of pollution and hydromorphological degradation have resulted to the formation of a relatively homogeneous macroinvertebrate community along the longitudinal gradient of the river, which was dominated by tolerant and generalist species accompanied with significant abundances. It was observed that disturbance retains assemblages between seasons where tolerant and generalist species dominated the community. The findings of this study indicated that local scale variables are more important than larger scale variables in structuring macroinvertebrate communities.