Saturated hydrocarbons in the sediments of Lake Apopka, Florida

Lake Apopka sediments were analyzed for n-alkanes and total organic carbon (TOC) from which long-chain hydrocarbon/short-chain hydrocarbon ratios (LHC/SHC) and LHC/TOC and SHC/TOC ratios were calculated. These ratios were used to distinguish the three types of organic sediments that originated historically mainly from byproducts of the primary producer community. These types are phytoplankton-derived sediments deposited during the hypereutrophic phase of the lake, macrophyte-derived sediments deposited during a low-nutrient, clear-water phase and transitional sediments deposited as the primary producer community shifted rapidly in the late 1940s from macrophyte dominance to phytoplankton abundance. The three ratios employed distinguish the three sediment types with exceptions that may result from a mixture of sediment types formed during the transition from macrophyte abundance to phytoplankton abundance. This study supports the hypothesis that the rapid shift from macrophyte dominance to phytoplankton dominance was induced by anthropogenic phosphorus loading. More detailed sampling and n-alkane analysis of cores from Lake Apopka have the potential to define when changes in the primary producer community occurred and to infer the temporal dynamics of the well-known shift in the primary producer community.