Given the complexity of interactions amongst human activities, climate change, and ecosystem feedback mechanisms, the new modeling tools are required to predict the ecosystem responses to management decisions especially in complex multi-basin systems, such as Lake Erie. Reducing total phosphorus (TP) loading to Lake Erie remains a key management tool to control eutrophication and associated ecological impacts, but since the late 1990s, the coupling of the lake’s ecological responses to external TP loading has become more tenuous suggesting a growing role of other drivers of Lake Erie’s eutrophication symptoms. To shed light on this issue, we constructed a long-term (2003-2016) average TP budget for both the whole lake and the individual basins and connecting channels. The TP budget implied the existence of significant, but yet uncategorized, in-lake TP sources that, together, amount to about one third of the total TP load to the water column, or about half the size of the external TP loading from the watershed. The mean water and TP residence times derived from the TP budget were used to derive TP load–response relationships and response matrices to predict steady state lake TP concentrations as a function of variable external TP inputs. The relationships were then extended to predict the trophic-level related water quality and ecosystem indicators. These relationships and matrices provide a simple but robust framework to gauge the potential long-term impacts of TP reduction interventions on Lake Erie’s TP concentrations and associated environmental indicators.

Authors:

Serghei Bocaniov, University of Waterloo  (sbocaniov@uwaterloo.ca)

Philippe Van Cappellen, University of Waterloo  (pvc@uwaterloo.ca)