The lower Green Bay Area of Concern (AOC) experiences frequent seasonal accumulations of cyanobacteria known as cyanobacterial harmful algal blooms (cyanoHABs). Some cyanoHAB species are known to produce one or more toxins, or cyanotoxins, harmful to human and environmental health. The beneficial use impairments listed in the AOC remedial action plans are due in part to the occurrence of cyanoHABs and potential for cyanotoxins to occur at unsafe levels. However, few studies have fully characterized cyanoHABs and their toxins in the lower Green Bay AOC. In this five – year study the objectives were to identify the severity and temporal trends of cyanoHABs and their toxins in the AOC as well as to investigate beach health risk predictive tools for estimating recreational risk.
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Boxplots of average chlorophyll and total phosphorus across all AOC sites in each year of the study. The edges of the boxes are the first and third quartiles while the whiskers represent the minimum and maximum without outliers and outliers are represented by circles. Two extreme outliers were removed from the 2019 chlorophyll data. The red dashed line shows the concentration threshold for a eutrophic condition according to Carlson’s index.
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Trends in surface water temperature (0 to 2 m) in lower Green Bay in each year. Shown are the average temperatures across four limnetic sites in lower Green Bay.
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Average relative abundance of the most abundant phytoplankton taxa in the lower Green Bay AOC based on cell density during the open water seasons 2016 – 2018. An asterisk denotes those genera often associated with production of one or more toxins.
Heatmap showing the concentration of algal toxin congeners detected by week of sampling and averaged across six sites (GBBB, GBJP, GB16, GB41, GB22, GB32) and five years (2016 – 2020). Week 24 is mid- July and week 40 is mid- September. MC = microcystins, C = cyanopeptolin, Apt = anabaenopeptins
Concentrations of microcystins exceeded the EPA recreational criterion threshold value of 8 µg/L on 0 – 4% of sampling days, depending on sampling site, which translates into 0 to 2 exceedances of this threshold in any given weekly assessment period. The greatest frequency of exceeding this threshold was at Joliet Park (GBJP) and Bay Beach (GBBB) locations. Exceedances of the EPA recreational guideline for microcystins occurred on average in month 8.7 (end of August) but with large variation of +/- 30 days
The Green Bay East buoy provides real time weather and water quality data on conditions in the lower Green Bay AOC including detection of harmful algal blooms. Current year data is available at lakestat.com . The buoy also features a high resolution video camera that takes one to three minute videos every hour. Archived buoy videos can be found here.