LAKERS TOGETHER: COVID vaccine required by September 30. Face coverings required indoors.
Muskegon Lake Internal Phosphorus Loading
Muskegon Lake was listed as a Great Lakes Area of Concern (AOC) in 1985 due to a long history of environmental abuse. Ultimately, nine beneficial use impairments (BUI) were designated for Muskegon Lake, including eutrophication or undesirable algae. Given the many years of discharge from various industries located on the shoreline directly into the lake, total phosphorus (TP) concentrations became elevated, and were averaging >60 μg/L in 1973, indicative of eutrophic conditions.
In the early 1970s, point source discharges were regulated through the Federal Clean Water Act, and over time the TP concentrations have declined in Muskegon Lake. In the past few decades, TP concentrations have been averaging close to or below 25 μg/L, which was established as the restoration target to remove the eutrophication BUI for the lake. However, P levels have increased slightly over the past few years, and recent results obtained from the Muskegon Lake Observatory (https://www.gvsu.edu/wri/buoy) suggest that mid-summer hypoxia in the lake may be inducing phosphorus release from the sediments (internal phosphorus loading).
Internal phosphorus loading can delay the recovery of lakes, even after external loading is managed, as diffusion or wind-wave action can promote P release from the sediment into the water column. When sediment phosphorus release is a significant source to the lake, then new management strategies may be needed to maintain TP concentrations below the restoration target.
Our study was designed to determine the importance of internal phosphorus loading as a source of P to Muskegon Lake. We collected sediment cores from three locations using established protocols, and measured sediment P release rates and sediment P fractions.
In July 2020, AWRI collected sediment cores from three sites in Muskegon Lake – two sites within the lake’s previously determined summer hypoxic zone and one site in a littoral hypoxic site on the lake’s southern shore. Cores were brought back to the lab, incubated, bubbled with either filtered air (oxic conditions) or N2-CO2 mixed gas (hypoxic conditions) for one month. Water samples were collected from cores at regular intervals, analyzed for phosphorus content, and used to calculate phosphorus release rates. Core sediment was analyzed for sediment TP, organic matter, and sediment-bound metals. Subsamples of sediment were sequentially analyzed for P fractionation.
Funding for this work was provided by NOAA/Great Lakes Commission Partnership.
Kathy Evans (WMSRDC)
Rick Rediske and Brian Scull (GVSU-AWRI)
Anthony Weinke and Jasmine Mancuso (GVSU-AWRI)