A multi-proxy trophic state reconstruction for shallow Orange Lake, Florida, USA: possible influence of macrophytes on limnetic nutrient concentrations

We retrieved four sediment cores from shallow, eutrophic, macrophyte-domina ted Orange Lake (A = 51.4 km(2), z(max) < 5 m, z(mean) < 2 m), north-centra l Florida, USA. The Pb-210-dated profiles were used to evaluate spatial and temporal patterns of bulk sediment and nutrient accumulation in the limnet ic zone and to infer historical changes in lake trophic state. Bulk density , organic matter, total carbon, total nitrogen, total phosphorus and non-ap atite inorganic phosphorus (NAIP) concentrations displayed stratigraphic si milarities among three of four cores, as did accumulation rates of bulk sed iment, organic matter and nutrients. Accumulation rates were slower at the fourth site. Nutrients showed generally increasing rates of accumulation si nce the turn of the century. Percentages of periphytic diatom taxa increase d progressively in the cores after similar to 1930. Diatom-inferred limneti c total P trends were similar among profiles. Eutrophic conditions were inf erred for the period prior to the turn of the century. The lake was hypereu trophic in the early decades of the 1900s, but inferred limnetic total P va lues declined after similar to 1930. Declining inferred limnetic total P tr ends for the last 60-70 years were accompanied by concomitant increases in accumulation rates of total P and NAIP on the lake bottom. Several lines of evidence suggest that after similar to 1930, phosphorus entering Orange La ke was increasingly utilized by submersed macrophytes. Paleolimnological re cords from Orange Lake highlight the importance of using multiple sediment variables to infer past trophic state and suggest that aquatic macrophytes can play a role in regulating water-column nutrient concentrations in shall ow, warm-temperate lakes.