Phosphorus Dynamics and Availability in the Nearshore of Eastern Lake Erie: Insights From Oxygen Isotope Ratios of Phosphate

Blooms of filamentous benthic algae that plagued Lake Erie in the 1950s through 1970s were largely reduced through reductions of phosphorus (P) loading from point sources. Since the mid-1990s, these blooms have returned despite a period of relatively stable external P inputs. While increased loadings of dissolved P have been causally linked to cyanobacterial blooms in some parts of the lake, the impacts of ecosystem changes such as the effect of invasive species on nutrient cycling and availability have not been fully elucidated, leading to uncertainty as to the effectiveness of additional non-point P management actions. Here we use the oxygen isotope ratios (δ18OP) of phosphate in concert with measures of water quality along the northern shore of the east basin of Lake Erie to identify sources and pathways of P cycling and infer potential importance in relation to annual blooms of Cladophora that foul the shorelines of eastern Lake Erie. δ18OP data indicate that potential external source signatures are rapidly overprinted by biological cycling of P by the plankton community and that much of the available phosphate in the nearshore waters is derived from hydrolysis of dissolved organic P compounds. Near the dreissenid-colonized lake bed, δ18OP was persistently and significantly enriched in 18O relative to δ18OP measured in surface waters and was similar to δ18OP of phosphate excreted by dreissenid mussels in incubations. These results implicate dreissenid mussels as key agents in nearshore P cycling and highlight the importance of considering ecosystem changes in the development of nutrient management strategies designed to ameliorate symptoms of eutrophication.

For more information and data please visit:https://open.canada.ca/data/en/dataset/4497ebe5-f45e-4b13-9e98-e9edd016fc66

Supplemental Information

Phosphorus is the primary nutrient which can cause excessive algal growth in freshwater. In the 1960’s and 70’s excessive nuisance algae, primarily Cladophora, washed up on beaches around the Great Lakes leaving large odiferous piles unaesthetically pleasing to Canadians seeking recreational activities at nearby Great Lake beaches. The first signing of the Great Lakes Water Quality Agreement established a commitment between the US and Canada to address water quality concerns including nuisance algae. One of the primary outcomes of the Great Lakes Water Quality Agreement (GLWQA) was the limiting of phosphorus inputs into the Great Lakes primarily from detergents and thereby decreasing the biomass of Cladophora in the great lakes. However, in the mid-1990s resurgence in Cladophora biomass occurred as well as toxic cyanobacteria blooms. The Great Lakes Nutrient Initiative (GLNI) provides funding to address the complexities of recurring toxic and nuisance algal blooms in the Great Lakes specifically Lake Erie.

For more information please visit: https://www.canada.ca/en/environment-climate-change/services/sustainable-development/strategic-environmental-assessment/public-statements/great-lakes-nutrient-initiative.html