Simulated impacts of climate change and agricultural land use change on surface water quality with and without adaptation management strategies

The impacts of climate and land use changes that may affect the quality of surface water in the future were quantified to identify the relative importance of each change. Sustainable field management practices were examined for their effectiveness to improve water quality in the future under the combined changes, to integrate the strategies into water management plans. In this modelling study, scenarios of climate change and land use change were therefore applied alone, and in tandem, in the hydrological model SWAT (Soil and Water Assessment Tool) to simulate the impacts on streamflow, sediments, total phosphorus (TP) and nitrate-nitrogen (NO3−-N) for a 2050 time horizon in the 629 km2 Pike River watershed located in southern Québec/northern Vermont. The combined climate and land use change scenarios simulated TP concentrations to be higher during January and February, but to be lower during April, compared to the reference simulation (1971-2000). Yet, the TP water quality criterion of 0.02 mg/L was always surpassed. On the other hand, the NO3-N concentrations were lower than the reference simulation during 8 months out of the year, only rarely exceeding the water quality criterion of 10 mg/L. When field management strategies were simulated to reduce the impacts, the mean annual sediments and TP loads were reduced particularly in winter. Despite the load reductions, the 0.02 mg TP/L criterion remained exceeded in each month (similar to values in the reference simulation). The future NO3−-N concentrations remained below 10 mg/L. This study demonstrates that both climate and land use change should be considered together to account for synergistic impacts to water quality, and that sustainable management strategies are effective adaptations to safeguard water quality from future changes that may occur in a watershed.