Cyanobacteria growth in the Western Lake Erie Basin (WLEB) has been a concern closely monitored over the past 10 years. The presence of cyanobacteria leads to a pea soup appearance of water that causes aesthetic concerns. Cyanobacteria also produce toxins which cause human health concerns, especially contact during recreational uses or at municipal water intakes. This article compares the 2016 bloom to years back to 2002, plus identifies target loadings for the WLEB to lessen the incidence of blooms.
Figure 1. Bloom severity index for 2002-2016 (green bar) plus the forecast for 2016 released in early July, 2016 (red bar) (Stumpf, 2016).
The historical bloom severity for 2002 through 2015 is seen in Figure 1 (Stumpf, 2016). The index is based on the amount of biomass over the peak 30-days. The 2016 severity forecast released on July 7, 2016 with the red bar showing a predicted value of 5.5 with an uncertainty range of 3-7. The actual observed level is shown with the green bar with a severity of 3.2 which was similar to 2004 and 2012. The highest observed levels were 2011 rated a 10 and 2015 with a rating of 10.5.
Spring loadings (1 March to 31 July) of bioavailable phosphorus entering the WLEB from the Maumee Watershed are a key factor in the severity of cyanobacterial blooms during the summer. This value is a key component of the predictive models of bloom size. Bioavailable phosphorus includes the dissolved reactive phosphorus (DRP) which is 100% soluble, plus an estimated portion of particulate phosphorus that will become available as water moves downstream and out into the lake. Figure 2 (Stumpf, 2016) below shows spring loading of bioavailable phosphorus for key reference years. In 2015, where severity reached 10.5, spring loading was over 700 metric tons. In 2004, where loading was close 250 and 2016 with close to 200 metric tons had a severity index around 3.0.
Figure 2. Total bioavailable phosphorus from the Maumee River for 2016 compared to some other years. Data collected by Heidelberg University (Stumpf, 2016).
Phosphorus, regardless of source, is an important factor in the presence of cyanobacteria blooms in the WLEB. Agriculture as a prominent land use in the WLEB has an important role to play to attain reductions through implementation of Best Management Practices for nutrient use and water management. All who live in the watershed should look for ways to lower contributions of phosphorus leaving their property.
Target Phosphorus Reductions for the Western Lake Erie Basin
Target loading criteria have been adopted by both the US and Canadian governments. The targets are designed to attain levels of cyanobacteria blooms that are less intrusive. The targets are set to achieve a bloom no greater than that observed in 2004 or 2012, 90% of the time.
To attain that target bloom level, the Task Team recommended P levels seen in Table 1 (Annex 4, 2015).
· Total phosphorus (TP) spring load of 860 metric tons and dissolved reactive phosphorus (DRP) loading of 186 metric tons from the Maumee River. (The 860 metric ton target is approximately a 40% reduction from the 2008 spring load of 1400 metric tons for TP and 310 metric tons of DRP.)
· Flow Weighted Mean Concentration (FWMC) of 0.23 mg/L for TP and 0.05 mg/L for DRP. (This target is expected to achieve phosphorus loadings below the targets (860 and 186 metric tons) 90% of the time (9 years out of 10), if precipitation patterns do not change.)
· Total P annual loading into the Lake Erie’s western and central basin of 6000 MT.
Table 1. Target P loading criteria for the Lake Erie (Annex 4, 2015).
Stumpf, R, (et.al). Harmful Algal Blooms in Lake Erie - Experimental HAB Bulletin. (2016) https://www.glerl.noaa.gov//res/HABs_and_Hypoxia/lakeErieHABArchive/
Annex 4 Objectives and Targets Task Team Final Report to the Nutrients Annex Subcommittee. (2015) https://www.epa.gov/sites/production/files/2015-06/documents/report-recommended-phosphorus-loading-targets-lake-erie-201505.pdf