Phosphorus Provenance and Cladophora in the Northern Lake Ontario Nearshore

Session: 31. - Evaluation of the Current State of Ecological Modeling and Future Perspectives

Anika Kuczynski, National Institute of Water and Atmospheric Research, [email protected]
Martin Auer, Dept. of Civil Engineering, Michigan Techn. University, [email protected]

Abstract

Despite implementation of phosphorus controls beginning in the 1970s and subsequent success in curbing algal growth, nuisance algae once again burden nearshore regions in the Laurentian Great Lakes. Historically, target phosphorus loads were determined based on the assumption that the lakes behaved as well-mixed systems in which whole-lake (offshore) concentrations drive algal growth. Today, offshore phosphorus concentrations are much lower, indicating that an understanding of local phosphorus sources (provenance) and a shift from the current management paradigm are required. We examined the sources of phosphorus driving nuisance Cladophora growth in the Ajax, Ontario region of northern Lake Ontario: offshore concentrations, tributary loads, wastewater treatment plant discharges, and phosphorus supply by dreissenids. We completed field surveys of conductivity, nitrate, phosphorus, and algal stored phosphorus content. Particulate and soluble phase bioassays were completed to determine phosphorus bioavailability of tributary and point sources. We found the local wastewater treatment plant to be the main source of bioavailable phosphorus to the Ajax nearshore. Management decisions based on whole-lake modelling can no longer ensure success at the local scale. Instead, high resolution mechanistic modelling is required to account for nutrient transport (hydrodynamics), fate (P transformation and bioavailability), and receptor (algal) response at the local scale.

1. Keyword
Cladophora

2. Keyword
Lake Ontario

3. Keyword
phosphorus