Macroinvertebrate community structure of small ditches in relation to the potential of pesticide drift exposure: Presentation held at the 12th SETAC Europe Meeting. Vienna, May 2002

The macroinvetebrate community of small ditches was sampled in 40 sites of the agricultural region Altes Land near Hamburg, Germany. The ditches were located along Greenland, old, unused apple orchards, integrated apple orchards, or organic apple orchards. Samples were taken on five dates over two years. In addition to the biological data, water chemistry and structural parameters were measured. A potential of drift exposure for each sampling site was calculated based on distance of the ditch to the last row of trees, as well as depth and width of the ditch. The range of pesticides applied in the orchards included organic and inorganic products, some of which are classified as very highly toxic to aquatic organisms, and all rows of the orchards were treated. Sites were grouped into no, low and high drift potential with the distance between orchard and ditch as the most important factor. A distance of less than 3 m characterized sites of the high drift group. Prinicpal Response Curves were calculated to show differences of community structure between these three groups over time . The ordination resulted in significant differences between the high drift sites and the no, respectively low drift sites, which were pronounced more in summer than in spring and autumn. There were no major differences between no and low drift sites, i.e. on sampling sites with a minimum distance of 3 m. Univariate analyses also showed effects correlated to the estimated drift exposure: the number of taxa as well as the abundance of some species and orders decreased with the drift potential. Isopoda, Ephemeroptera, insects in total, and Eulamellibranchiata were identified as the most sensitive taxa