NSF Award
2427185
This research examines how long-term changes in agriculture affect streams and lakes, using an Ohio landscape as a model system. In Acton Lake, the amount of algae is controlled mostly by concentrations of suspended sediments (SS) in the water (because SS block light that algae need), nutrients entering from streams, and the abundance of bottom-feeding fish (these fish consume sediments and excrete nutrients into the water). In the 1990s, the use of conservation tillage (reduced-tillage and no-tillage farming) increased greatly on farmland. This reduced soil erosion, and strongly affected nutrients and sediments in streams that enter Acton Lake. Also, the abundance of bottom-feeding fish in the lake increased. This project explores long-term changes in lake algae, related to changes agriculture and the abundance of sediment-feeding fish. The research is important because similar agricultural changes are occurring throughout the US, but little is known about long-term effects on streams and lakes. Thus, this research will help inform management of agriculture and water quality. The project includes a significant student training component, as well as public outreach.<br/><br/>This project explores temporal dynamics in ecosystem subsidies and their consequences. After conservation tillage increased in the 1990s, tillage was stable for 10-15 years, but then decreased in recent years. Biomass of detritivorous fish (gizzard shad), and therefore their nutrient excretion, increased over roughly the first 12 years, then was stable until an increase in recent years. Over the first decade, concentrations of phosphorus (P) and SS in streams declined. Lake phytoplankton biomass increased greatly, due to reduced light limitation (because of decreased SS in the lake) and increased excretion by fish. However, over the next 10-15 years, stream concentrations of dissolved P increased, stream nitrate and SS decreased, and lake phytoplankton biomass has been relatively stable. During this period, phytoplankton have become increasingly N-limited and less P-limited. The shift in nutrient limitation coincides with decreasing N:P in streams, and increased excretion by fish, whose fecal content has a low N:P. The project explores several predictions: 1) in streams, dissolved P will continue to increase while nitrate declines; 2) gizzard shad excretion rates will remain high; 3) phytoplankton will become more N-limited and less P-limited; and 4) phytoplankton biomass will be stable, or will decline as N becomes more limiting. The project will provide mentoring for several undergraduate and graduate students who will conduct research projects, targeting students from underrepresented groups, and will implement several outreach activities for the general public and farmers.<br/><br/>This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
