Historical ecology of a hypereutrophic Florida lake.

Lake Hollingsworth lies in phosphate-rich central Florida. Recent limnological data show the lake has been hypereutrophic for \u3e25 years, but nothing was known of the lake\u27s trophic history prior to the late 1960s. A paleolimnological study was undertaken to: 1) evaluate the distribution of organic sediments in the basin, 2) reconstruct historical water quality to determine whether the lake is naturally (edaphically) or anthropogenically nutrient-rich, and 3) assess the feasibility of reducing in-lake nutrient concentrations. Organic sediments are distributed rather uniformly above the sandy substrate. Two 210Pb-dated sediment cores taken ≈0.7 km apart display similar stratigraphies with respect to density, organic matter, total C, N, P, radioisotopes, biogenic SiO2, diatoms and δ13C in organic matter. Limnetic Ptot reconstructions, inferred from diatoms, show eutrophic (≈30 μg L−1) conditions in the late 1800s. Total P increased after 1920 and very high Ptot concentrations (125 to \u3e200 μg L−1) are inferred for the 1950s through 1970s. Cultural eutrophication was probably a consequence of agriculture, residential development, construction of Florida Southern College, road building, stormwater runoff and regional phosphate mining. Total P inferences in the 1980s declined to ≈65 μg L−1, reflecting soil stabilization and reduced mining activity. The historical perspective provided by paleolimnological data demonstrates that Lake Hollingsworth was naturally eutrophic, but became hypereutrophic as a consequence of anthropogenic nutrient loading. It is probably not feasible to reduce in-lake nutrient concentrations significantly in this shallow, urbanized, hypereutrophic waterbody