Aquatic macroinvertebrates in the altes land, an intensely used orchard region in Germany: Correlation between community structure and potential for pesticide exposure.

To assess the impact of pesticides on aquatic organisms under realistic worst-case conditions, a macroinvertebrate community of small ditches was sampled at 40 sites of the orchard region Altes Land near Hamburg, Germany. To differentiate between pesticide impact and other variables, the ditches selected for sampling were located at different distances along grassland, unused apple orchards, and orchards managed with integrated and/or organic crop protection methods. Samples of macroinvertebrates were taken on five dates over two years. In addition to biological data, water chemistry and structural parameters were measured. For each sampling site, a potential for exposure was calculated on the basis of the distance of the ditch to the nearest row of trees and the depth and width of the ditch. The neighborhood to either grassland or orchards turned out to have a larger impact on the macroinvertebrate community than the potential for exposure. Therefore, grassland sites were omitted from further evaluation. Remaining sites were grouped into low exposure (sites at unused orchards), medium exposure (distance of 3-5 m [track] between trees and ditch), and high exposure (trees close to the ditch, mean distance < or = 1.5 m). Principal response curves showed differences in community structure between the three exposure groups over time. Whereas for sites from the high exposure group significant differences from low exposure was observed in all seasons, significant differences between low and medium were observed only occasionally. Effects were less pronounced in samples taken at springtime before the starting pesticide applications, suggesting some community recovery. Species richness was negatively correlated to exposure potential. Isopoda, Eulamellibranchiata, and insects, especially Ephemeroptera, showed a high negative correlation with the potential for pesticide exposure, suggesting that these taxa are sensitive to the pesticide use in the orchards.