H223-02
Effect of rising mean water levels on mobility and discharge of nutrients to coastal waters
Effect of rising mean water levels on mobility and discharge of nutrients to coastal waters
Thursday, 17 December 2020: 05:34
Virtual
Abstract:
Climate change induced variations in coastal water levels, wave climate, and temperature will influence the hydrological and geochemical conditions in nearshore coastal aquifers. Prior studies have shown that metal oxides (e.g. iron oxides) that form near the groundwater-coastal water interface in nearshore aquifers act as a sediment trap for reactive pollutants of environmental concern (e.g. arsenic, mercury, phosphorus) preventing their discharge to surface waters. These sediment traps are dynamic systems and therefore their ability to trap pollutants may change in response to changing hydrological and geochemical conditions. These sediment traps may switch over time from storing pollutants and providing a net decrease in pollutant flux to coastal waters to becoming sources that release pollutants and exacerbate coastal water pollution. The study objective was to evaluate the impact of changing mean coastal water levels on the functioning of the reaction zone and subsequent mobility of pollutants in a nearshore aquifer and their discharge to inland coastal waters. Inland coastal waters provide an ideal setting to examine this potential impact due to high long-term interannual variability in water levels compared to marine environments where long-term sea level rise is predicted.
Field investigations were conducted in summer 2015 and summer 2020 in a permeable nearshore aquifer on Lake Huron, Canada with these sampling times representing periods of historically low and high lake water levels, respectively. The mean water level increase between sampling events was ~2 m. Previous investigations revealed a septic system derived nutrient plume at the field site with this current study showing how the change in mean water levels has modified the fate of nutrients in the plume, their discharge pathway, and their release to the nearshore water. The study findings are needed to understand the impact of changing water levels on pollutant release to coastal waters and inform long-term water quality predictions and management. While this study focuses on nutrients, the findings are relevant for other reactive pollutants of concern in coastal settings.
Field investigations were conducted in summer 2015 and summer 2020 in a permeable nearshore aquifer on Lake Huron, Canada with these sampling times representing periods of historically low and high lake water levels, respectively. The mean water level increase between sampling events was ~2 m. Previous investigations revealed a septic system derived nutrient plume at the field site with this current study showing how the change in mean water levels has modified the fate of nutrients in the plume, their discharge pathway, and their release to the nearshore water. The study findings are needed to understand the impact of changing water levels on pollutant release to coastal waters and inform long-term water quality predictions and management. While this study focuses on nutrients, the findings are relevant for other reactive pollutants of concern in coastal settings.