Agricultural ditches are some of the first systems exposed to runoff and can be a key to conservation efforts attempting to decrease lake eutrophication. There are three types of agricultural ditch management: conventional, two stage, and self-forming streams. In this study, we examine a variety of ditch components to determine which type of ditch best retains nitrogen and phosphorus. We hypothesize that ditch management partly influences nutrient loading by altering flow permanence, vegetation, and, as a result, animal abundance and diversity. We predict that two-stage ditches will have high vegetation and flow permanence, fostering better habitat for a diversity of animals, therefore increasing nutrient removal via insect emergence, compared to other ditches. To test this hypothesis, we conducted a field experiment collecting surface water, sediment, plants, and macroinvertebrates to analyze for nutrients in spring and mid-summer. Multiple samples were taken from all three types of ditches as well as natural streams for comparison. We also plan to conduct a lab experiment to test invertebrate bioturbation effects on sediment and surface water nutrients. We plan to run this experiment using crayfish, isopods, and midge larvae as the bioturbators of separate sand and clay sediments.
Results/Conclusions
Preliminary results show self-forming streams have the highest average biomass of both channel and bank plants per square meter. Surface water results show that phosphorus increased as it moved downstream in spring, and decreased in mid-summer. Nitrogen did not show such clear seasonal trends among all ditch types. These seasonal differences in nutrients may correspond to the relative influence of vegetation under different hydrological conditions.