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Nutrient Limitation of Oklahoma Reservoirs: Potential Effects of Watershed Land Use and Iron

Nutrient Limitation of Oklahoma Reservoirs: Potential Effects of Watershed Land Use and Iron

Name:
Felicia Osburn

Department:
Zoology

Abstract:
Eutrophication of Oklahoma reservoirs is becoming an important issue, especially in summer months when algal growth is normally at its highest. Historically, it has been found that phosphorus (P) is the limiting nutrient for primary production in reservoirs, and many efforts to control eutrophication have been limited to such. However, recent research suggests that other nutrients including nitrogen (N) and iron (Fe) may also be important and limit primary production at least in some systems. Furthermore, the limiting nutrient may be dependent on external nutrient inputs and the makeup of a reservoirs watershed. In this study, 25 reservoirs where chosen with increasing percentages of crop/hay in their watersheds across Oklahoma and nutrient bioassays (1 L jars with filtered reservoir water and ran for 5 days) were conducted to determine how P, N, and Fe affected algal biomass. We found that there were positive correlations between having a high percentage of crop/hay in the watershed and concentrations of P, N, and chlorophyll a in the water column. In most reservoirs, N and P co-limited algal biomass while P was the sole limiting nutrient in only one reservoir. Similarly, Fe was only important as a co-limiting factor with both N and P in only three reservoirs. Combined, these results suggest it is beneficial to consider N as a limiting factor towards reservoir eutrophication.