Assimilation of Phosphorus from a Point Source in the Lake Michigan Nearshore Zone

Session: 48. - Physical Ecology in Large Lakes and their Watersheds

Hector Bravo, University of Wisconsin-Milwaukee, [email protected]
Harvey Bootsma, University of Wisconsin-Milwaukee, [email protected]
Bahram Khazaei, Univeristy of Wisconsin-Milwaukee, [email protected]

Abstract

Nutrient loading into Lake Michigan can produce algal blooms, hypoxia, beach closures, clogging of water intakes, and reduced water quality. The Great Lakes Water Quality Agreement targets for Lake Michigan are 5600 MT annually for total phosphorus (TP) loading, 7 ?g L?1 lake-wide mean TP concentration in spring, and a chlorophyll-a concentration of 1.8 ?g L?1. However, in light of the resurgence of nuisance algal (Cladophora sp.) growth in the nearshore zone, the validity of these targets is now uncertain. Regulating agencies are looking for guidance in the quantification of the lake assimilative capacity, which entails finding the relations between wastewater treatment plant TP loading, and to-be-defined relevant time scale, and evaluation zone where the lake target may be exceeded. The occurrence and abundance of Cladophora depends on the availability of phosphorus, water clarity and temperature, and recently on the presence of mussels. The availability of excess phosphorus can be used as an indicator of nearshore areas susceptible excessive Cladophora growth and impaired water quality. This study built on a previously validated nearshore hydrodynamic model to develop a nearshore biogochemical model that simulates the interactions among hydrodynamic transport of phosphorus, Cladophora growth and biomass, mussel nutrient cycling, and sediment dynamics.

1. Keyword
Cladophora

2. Keyword
Lake Michigan

3. Keyword
modeling

4. Additional Keyword
Mussel

5. Additional Keyword
Nearshore processes

6. Additional Keyword
Nutrients