Abstract
Cyanobacterial harmful algal blooms and the toxins they produce are a global water-quality problem. Monitoring and prediction tools are needed to quickly predict cyanotoxin action-level exceedances in recreational and drinking waters used by the public. To address this need, data were collected at eight locations in Ohio, USA, to identify factors significantly related to observed concentrations of microcystins (a freshwater cyanotoxin) that could be used in two types of site-specific regression models. Real-time models include easily or continuously-measured factors that do not require that a sample be collected; comprehensive models use a combination of discrete sample-based measurements and real-time factors. The study sites included two recreational sites and six water treatment plant sites. Real-time models commonly included variables such as phycocyanin, pH, specific conductance, and streamflow or gage height. Many real-time factors were averages over time periods antecedent to the time the microcystin sample was collected, including water-quality data compiled from continuous monitors. Comprehensive models were useful at some sites with lagged variables for cyanobacterial toxin genes, dissolved nutrients, and (or) nitrogen to phosphorus ratios. Because models can be used for management decisions, important measures of model performance were sensitivity, specificity, and accuracy of estimates above or below the microcystin concentration threshold standard or action level. Sensitivity is how well the predictive tool correctly predicts exceedance of a threshold, an important measure for water-resource managers. Sensitivities > 90% at four Lake Erie water treatment plants indicated that models with continuous monitor data were especially promising. The planned next steps are to collect more data to build larger site-specific datasets and validate models before they can be used for management decisions.
Highlights
The increasing prevalence of cyanobacterial harmful algal blooms and the toxins they produce are a global water-quality issue that threatens human and wildlife health and necessitates additional monitoring of recreational and drinking water source waters (Harke and Gobler 2015; O’Neil et al 2012)
Microcystin concentrations found at MBSP Beach ranged from < 0.30 to 240 μg/L, necessitating a split of the y axis to adequately view the range of microcystin concentrations
Sensitivities > 90% at four Lake Erie water treatment plant (WTP) indicated that models with continuous monitor data were especially promising (Table 4)
Summary
The increasing prevalence of cyanobacterial harmful algal blooms (cyanoHABs) and the toxins they produce are a global water-quality issue that threatens human and wildlife health and necessitates additional monitoring of recreational and drinking water source waters (Harke and Gobler 2015; O’Neil et al 2012). Identifying monitoring and prediction tools to help make informed decisions on the potential occurrence of harmful levels of toxins in recreational and drinking waters used by the public is an immediate need. To provide warnings of potential cyanoHAB occurrence, area water managers have proactively turned to the HAB Bulletin, a bi-weekly forecast of cyanobacterial density based on remote sensing of cyanobacterial pigments (National Oceanic and Atmospheric Administration–Great Lakes Environmental Research Laboratory 2019). Microcystins, are not pigments and cannot be directly detected by remote sensing (Stumpf et al 2016)
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