MODELING AND UNDERSTANDING GROUNDWATER CONTAMINATION CAUSED BY CYANOTOXINS FROM HARMFUL ALGAL BLOOMS IN LAKE ERIE

Cyanotoxins, which are produced and released into the surrounding water during harmful algal blooms (HABs), can severely deteriorate water quality and cause health-related issues and economic loss. HABs and cyanotoxin studies have typically focused on surface-water domain (e.g., lakes, estuaries, and rivers), with few investigating or reporting on groundwater. This study aims to explore whether groundwater can be contaminated by cyanotoxins (microcystins) from HABs in surface water due to the surface-water and groundwater interaction. Specifically, we created a 3-dimensional MODFLOW model to simulate pumping-induced reverse groundwater flow and solute transport from Lake Erie to aquifer underneath the South Bass Island, Ottawa County, Ohio. Simulation results show that, under a typical setting (hydraulic conductivity: 1 m/day; pumpage: 125 m³/day; distance of pumping well from lake: 17 m), it would take about 14 days for microcystins to be found in the groundwater supply well at a detectable level (0.1 μg/L), following an occurrence of high concentration HABs event in the lake (i.e., 3 mg/L on July 24, 2015). For the same well to reach EPA’s advisory levels for infants and children (0.3 μg/L) and school-age children to adults (1.6 μg/L) for microcystins, it would take about 21 and 53 days, respectively. Such preliminary results and findings clearly suggest that HABs in the Great Lakes could contaminate groundwater resources and supply in the vicinity. As a next step, we will apply the model to examine and understand which specific hydrogeologic settings and scenarios would particularly facilitate the reverse flow and transport of microcystins and thus worsen the contamination.