Author(s): Hector R Bravo, Harvey Bootsma, Bahram Khazaei
Linked Author(s): Hector Bravo
Keywords: Laurentian Great Lakes, limnology, nearshore processes, modeling, nutrients
Abstract: Nutrient loading into Lake Michigan can produce algal blooms, hypoxia, beach closures, clogging of water intakes, and reduced water quality. Addressing those problems requires the understanding of the transport and fate of phosphorus in lakes. Research has shown that reducing tributary phosphorus loading may reduce Cladophora abundance near tributary sources. There is active research on the influence of dreissenid mussel filtering on water clarity and phosphorus bioavailability in the nearshore, and the importance of nearshore-offshore phosphorus exchange. None of the existing models specifically accounts for the role of mussels in the phosphorus cycle despite evidence that this role is significant. We developed a computer model that simulates the hydrodynamic and biogeochemical processes relevant to the transport of phosphorus in the nearshore zone. We then used the Milwaukee Metropolitan Sewerage District (MMSD) South Shore Wastewater Treatment Plant (SSWWTP) as a case study, applying the model to simulate the transport of phosphorus released by the plant. The 3D model consists of a hydrodynamic model linked with a biogeochemical model. The hydrodynamic component is a high-resolution model of the lake nearshore zone around Milwaukee, nested into the National Oceanic and Atmospheric Administration Lake Michigan model. The biogeochemical model consists of three linked modules. The Cladophora module simulates near-bottom dissolved phosphorus uptake and respiration, and sloughing. The mussel module simulates near-bottom particulate phosphorus grazing, excretion to near-bottom dissolved phosphorus, and egestion to sediment storage. The sediment storage module simulates the particulate phosphorus settling and resuspension. The model was validated against the field measured water temperature, total and particulate phosphorus, Cladophora biomass, and phosphorus content. The study included the laboratory testing phosphorus samples with low detection limit and analysis of Cladophora trends in the nearshore zone. The model is being applied as a management tool to test the scenarios of SSWWTP nutrient loading, determining the effluent phosphorus limits for the treatment plant
Year: 2017