A Multilevel Model of TP-Chlorophyll-a for the Great Lakes: Understanding Annual Variability

Session: Harmful Algal Blooms: From Ecosystem Drivers to Ecosystem Impacts (1)

Polly Peterson, University of Toledo, [email protected]
Song Qian, University of Toledo, [email protected]
Paris Collingsworth, Purdue University, US EPA, [email protected]

Abstract

The relationship between phosphorous concentration (TP) and chlorophyll-a concentration (as an indicator of cyanobacteria abundance; Chla) has been well-established for temperate freshwater lakes.  It is often used to evaluate a lake's trophic status, especially the magnitude of the TP slope.  A preliminary analysis of the Chla-TP relationship using EPA Great Lakes National Program Office data from 1999-2016 showed a year to year variation in the relationship, particularly in the western basin, without a consistent temporal trend.  This indicates that there are additional factors that are influencing the variation in Chla in the lake.  Understanding the annual variations in the TP-Chla response by lake are important for uncovering the additional drivers of harmful algal blooms.  In this presentation, we expand the model to incorporate all five Great Lakes to better understand the larger trends and help to discern the mechanisms driving the year-to-year variation.