Abstract
Greenfield Lake in Wilmington, NC, has experienced recent problems with algal blooms, low dissolved oxygen levels, and fish kills, although various remedial actions have been taken that led to some visible improvements over the last decade. Many of these issues have likely been caused by high nutrient loading from the lake's urbanized watershed. The role of lake sediment as a source and a sink for phosphorus (P), which is often considered the nutrient most responsible for freshwater eutrophication, has not been examined. We identified and quantified the forms of P in the lake's sediments. Fourteen sites were sampled around the lake in 2012–2013. A sequential extraction procedure allowed analysis of five P forms of varying bioavailability. Total P concentrations in the sediment averaged 51.1 µg g−1 sediment, which is low relative to other lakes. The most concentrated P forms were the reductant-extractable, acid-extractable and residual P fractions. These results, and very low concentrations of more readily bioavailable P fractions, strongly indicate that the lake's abundant plant biota (phytoplankton, filamentous algae, and macrophytes) control and sequester most of the P load in the lake's water column. Further remediation efforts should consider the role of these plant populations in regulating the lake's water quality.
The Ecological Role of Interactions Between Plants in Agroecosystems
