Response of nearshore groundwater systems adjacent to large lakes to climate change

ABSTRACT: Nearshore groundwater systems play a key role in governing the exchange of pollutants across the land-lake continuum. Temperature rise, lake and groundwater level fluctuations, and increased frequency and intensity of extreme weather events associated with climate change will impact nearshore groundwater systems including the reactive processes occurring near the groundwater-lake interface. Prior studies have shown that metal oxides (e.g. iron oxides) that form near the groundwater-lake interface in nearshore aquifers act as a sediment trap for reactive pollutants of environmental concern (e.g. arsenic, phosphorus, mercury). This can prevent their discharge to adjacent nearshore waters. However, these sediment traps are not stable and may act as legacy pollutant sources whereby trapped pollutants may be released as environmental conditions change, thereby contributing to impairment of nearshore waters. The objective of this study was to explore how climate change may affect the function of these sediment traps and their ability to retain pollutants. This presentation will cover several examples from field and laboratory investigations of how climate change induced factors (e.g. change in lake water levels, increased storm events, change surface water chemistry) may impact the functioning of the sediment trap and potential discharge of pollutants to nearshore lake waters. Overall, it is predicted that release of trapped pollutants to coastal waters may occur if conditions in nearshore groundwater become more reducing, pH increases and/or shoreline erosion modifies the pollutant discharge pathway to nearshore waters. Study findings have broad implications for evaluating potential risks of groundwater discharge to nearshore water quality and ecosystems and in predicting nearshore water quality trends as the climate changes.