Protection & Restoration of Ecosystem Services

Overview and Objectives

In 2011, Lake Erie experienced a cyanobacterial bloom of unprecedented proportion (Michelak et al. 2013). This event, though noteworthy, was only one recent example of eutrophication symptoms that reappear in some areas of the Great Lakes more than 35 years after the establishment of phosphorus reduction targets under the 1978 Great Lakes Water Quality Agreement (GLWQA). Recognizing these enduring problems, the updated 2012 GLWQA calls for a reevaluation of the 1978 phosphorus targets. Additionally, the revised protocol directs Canada and the United States to “develop Substance Objectives for phosphorous concentrations for nearshore waters, including embayments and tributary discharge for each Great Lake” and to “complete this work for Lake Erie within three years of entry into force of this Agreement”. Thus, there is an imperative to focus attention on management actions that will reduce ongoing eutrophication problems, which include extensive hypoxia, in Lake Erie. While the fundamental drivers of algal proliferation in temperate lakes have been understood since the 1970s (Schindler 1977), there are lake-specific processes that influence the relationship between phosphorus and measures of algal productivity (Pace 1984, Stauffer 1991, Kamarainen 2008). Additionally, the Great Lakes have experienced profound changes since the initial phosphorus targets were developed in the 1970s. Most notably, invasive dreissenid mussels, which became abundant in the 1990s, have altered phosphorus cycling, promoted cyanobacterial growth (Vanderploeg et al. 2001) and altered the relationship between chlorophyll a and total phosphorus (Cha et al. 2013). Concurrently, phosphorus inputs to Lake Erie have changed with bioavailable phosphorus concentration increases in the western tributaries since the 1990s (Daloglu et al. 2012).

The objective of this study is to provide information that will support pending decision-making for Lake Erie nutrient and harmful algal bloom (HAB) management by developing predictive models that describe the relationship between phosphorus concentration and other logical predictor variables, and endpoints associated with algal production including cyanobacteria, Microcystis, and total algal biovolume, and chlorophyll a. Additionally, we will explore relationships between phosphorus inputs and in-lake phosphorus concentrations to examine whether the existing data support development of a simple network linking measures of algal concentration to watershed loads. Because phosphorus load is composed of tributary flow and phosphorus concentration, which have distinct effects on the distribution and concentration of in-lake phosphorus, we will consider these two drivers separately in the model development.