A Review and Evaluation of the Impacts of Climate Change on Geogenic Arsenic in Groundwater from Fractured Bedrock Aquifers

Climate change is expected to affect the groundwater quality by altering recharge, water table elevation, groundwater flow, and land use. In fractured bedrock aquifers, the quality of groundwater is a sensitive issue, particularly in areas affected by geogenic arsenic contamination. Understanding how climate change will affect the geochemistry of naturally occurring arsenic in groundwater is crucial to ensure sustainable use of this resource, particularly as a source of drinking water. This paper presents a review of the potential impacts of climate change on arsenic concentration in bedrock aquifers and identifies issues that remain unresolved. During intense and prolonged low flow, the decline in the water table is expected to increase the oxidation of arsenic-bearing sulfides in the unsaturated zone. In addition, reduced groundwater flow may increase the occurrence of geochemically evolved arsenic-rich groundwater and enhance arsenic mobilization by reductive dissolution and alkali desorption. In contrast, the occurrence of extreme recharge events is expected to further decrease arsenic concentrations because of the greater dilution by oxygenated, low-pH water. In some cases, arsenic mobilization could be indirectly induced by climate change through changes in land use, particularly those causing increased groundwater withdrawals and pollution. The overall impact of climate change on dissolved arsenic will vary greatly according to the bedrock aquifer properties that influence the sensitivity of the groundwater system to climate change. To date, the scarcity of data related to the temporal variability of arsenic in fractured bedrock groundwater is a major obstacle in evaluating the future evolution of the resource quality.