The effects of agricultural nitrate runoff on Chironomidae (Diptera)
St. Olaf College
A survey of nitrate concentrations in six lakes across southern Minnesota revealed considerable variation between study sites, ranging from 0.002 to 3.8 ppm NO3. ANOVA analysis of data obtained through GIS illustrated the impact of land use on nutrient variability, finding a significant positive correlation between water column nitrates and the total agricultural area in the lakeshed. Landscape characteristics such as lake surface area, total length of stream channels, and wetland buffer areas were found to mitigate the impact of nitrates in agricultural runoff. The implications of nitrate additions will be examined in further research involving the indicator insect family Chironomidae (Diptera). Chironomus dilutus bioassays and Nitrogen isotope measurements will determine the developmental and physiological effects of rearing in a range of nitrate solutions, while collection of floating pupal exuviae will indicate the Chironomidae species composition in each of the study lakes.