Great Lakes Fishery Commission

Updated 2021-09-23 16:19:06

Lake Erie -> 5.0 Environmental Objectives -> Lower Trophic Levels

Maintain mesotrophic conditions in the west, central, and nearshore waters of the east basin

The Lake Erie Committee Environmental Priorities (Lake Erie Committee 2019) identifies achievement of mesotrophic conditions in the west, central and nearshore east basin waters as the target to attain Lake Erie’s fish community objectives favoring production of percids (i.e., walleye and yellow perch; Francis et al. 2020). Mesotrophic conditions are characterized by an intermediate level of nutrient productivity. Nutrient conditions are described using measurements of total phosphorus, water transparency, and chlorophyll a, and are combined into a single indicator of nutrient condition called a trophic state index, or TSI (Leach et al. 1977, Carlson 1977). Mesotrophic conditions have a TSI value between 36.5 and 45.5.

Trends in nutrient status indicate that Lake Erie has increased in productivity during the 2016-2020 reporting period in the west and central basins but has remained steady in the nearshore waters of the east basin. The west basin has remained above the targeted mesotrophic conditions for the entire time series indicating an excess of nutrients, with an increasing trend during the reporting period (Figure 1). The central basin has generally remained within the targeted mesotrophic range for the entire time series, also with an increasing trend during the reporting period (Figure 2). The nearshore waters of the east basin were below the targeted mesotrophic conditions in the reporting period with no apparent trend (Figure 3).

Figure 1. Median trophic state indices (TSI) for the west basin of Lake Erie, 1999-2020. The target mesotrophic TSI range is between 36.5 and 45.5.

Figure 2. Median trophic state indices (TSI) for the central basin of Lake Erie, 1999-2020. The target mesotrophic TSI range is between 36.5 and 45.5.

Figure 3. Median trophic state indices (TSI) for the nearshore waters of the east basin of Lake Erie, 1999-2020. The target mesotrophic TSI range is between 36.5 and 45.5.