SECONDARY PRODUCTION OF BENTHIC STREAM INVERTEBRATES IN AGRICULTURAL WATERSHEDS WITH DIFFERENT LAND MANAGEMENT-PRACTICES

Annual secondary production of four coexisting caddisfly species (Trichoptera; Hydropsychidae: Hydropsyche spp.) was estimated in two adjacent branches of Kintore Creek, Ontario, Canada. The west branch was located in a demonstration watershed where conservation tillage was practiced i.e., mulch-finishing of row crops, planting of forage and cover crops, some no-till practices, etc. Conventional agricultural land management occurred in the watershed which drained into the east branch i.e., corn-wheat-alfalfa rotation with fall moldboard ploughing. Production estimates and densities of caddisflies were consistently higher in the watershed where conservation tillage was practiced. For example, mean annual production of H. slossonae was 12.02 g ash-free dry weight (AFDW)/m2 in the west branch vs. 2.45 g AFDW/m2 in the east branch. Differing concentrations of herbicides, insecticides and nutrients in the two watersheds are discussed as possible explanations for this pronounced difference in productivity.