Cross-Ecosystem Effects of Agricultural Tile Drainage, Surface Runoff, and Selenium in the Prairie Pothole Region

摘要

The Prairie Pothole Region (PPR) of the United States and Canada is a vast network of wetlands that provide rich habitat for waterfowl and aquatic organisms. Much of the landscape surrounding these wetlands is dominated by agriculture, allowing for contaminants such as neonicotinoid insecticides and selenium to enter these water bodies following precipitation. We surveyed 18 wetlands in the PPR of South Dakota that were categorized as receiving surface runoff, tile drainage, or surrounded by grassland (control) for larval and adult insects and contaminant concentrations over two years. Selenium concentrations in the water, as well as in larval and adult insects were the biggest difference among our treatments, and concentrations of all three were approximately two times higher in tile drainage sites than in surface or control sites. For example, adult insect tissue concentrations were (mu g/g, mean +/- S.D.) 1.5 +/- 1.3 in control sites, 1.7 +/- 2.4 in surface runoff sites, and 4.4 +/- 5.0 in tile drainage sites. Adult insects responded more sensitively to agricultural influences than larval insects, with up to 50% reductions in adult abundance in the tile drainage treatment even in the absence of larval population reductions. Reductions in adult populations in combination with the retention of selenium over metamorphosis indicate that agricultural influence in these wetlands may also affect the terrestrial ecosystem by reducing quantity and/or quality of insect prey for terrestrial consumers, such as waterfowl.