Role of contemporary and historic vegetation on nutrients in Missouri reservoirs: implications for developing nutrient criteria

Abstract

Jones, J.R., M.F. Knowlton, D.V. Obrecht, A.P. Thorpe and J.D. Harlan. 2009. Role of contemporary and historic vegetation on nutrients in Missouri reservoirs: implications for developing nutrient criteria. Lake Reserv. Manage. 25:111–118. Using vegetative survey records from the time of Euro-American settlement (circa 1815–1850) we found the proportion of historic prairie accounted for 42% of cross-system variation in total phosphorus (TP) and 48% of total nitrogen in 156 Missouri reservoirs. When combined with dam height (surrogate for lake morphometry) and hydraulic flushing rate (TP only), 56% of variation in nutrients was explained. Consistent with previous analyses, some two-thirds of variation in nutrients was accounted for by contemporary cropland, morphometry, and hydrology (TP only). Adding prairie or historic forest cover to models based on current cropland did little to increase explained variation. The relationship between reservoir nutrients and land cover is partly an artifact of past land conversion; most arable soils with inherent fertility sufficient to generate economically viable produce and suitable topography were former prairies. The cross-system analysis of Missouri reservoirs showed that nutrients in these anthropogenic ecosystems are largely determined by nonpoint input from current land use as modified by morphology and hydrology. Historic vegetation cover, however, was our best measure of baseline conditions in the reservoir catchments and contributes to the framework for developing nutrient criteria for these artificial lakes. No natural reference conditions exist for Missouri reservoirs, and we recommend setting site-specific nutrient criteria for these constructed systems.