Enhancing understanding of BMP effectiveness and land use change impacts on water quality, water quantity, and potato production in Atlantic Canada

Abstract

Excessive nitrate loading from agricultural non-point sources (NPS) is threatening the health of receiving waterbodies at a global scale. The intensive agricultural production in Atlantic Canada has consistently posed severe threats to aquatic ecosystems. Beneficial management practices (BMPs) are often implemented to mitigate environmental impacts from agricultural production. Reliable information of the effects of BMPs from field to watershed scale is needed to inform watershed management. Relating the drivers/sources of water and nitrogen movement in watersheds to spatial and temporal land uses patterns is therefore essential for developing effective mitigation strategies. This study investigated the environmental and economic impacts of agricultural BMPs and land use impacts on water quantity and quality. The objectives were to: i.) investigate nitrogen dynamics and leaching potential under conventional (potato-barley-red clover (PBC)) and alternative (potato-soybean-barley (PSB)) potato rotations in Prince Edward Island (PEI) through field experiments; ii.) to evaluate the effects of the soil and water conservation terrace on potato yield under northern New Brunswick climate conditions, using the Soil and Water Assessment Tool (SWAT); iii.) to explore the impacts of land use on water yield and nitrate load to surface water in an agricultural watershed in PEI using SWAT; iv.) to examine the performance of statistical models compared to SWAT in estimating nitrate load from sparsely measured nitrate data. Results suggested that: i.) alternative PSB rotation could increase potato yields while reducing N leaching, when compared to the conventional PBC rotation; ii.) Terrace could help to improve potato productivity by improving soil water availability during the growing seasons of dry and normal years; iii.) Land under potato rotation contributed 84.5% of the total nitrate load to the watershed. Land use demonstrated little impact on water yield but affected nitrate load significantly, while climatic variables of temperature and precipitation were the top two factors affecting water yield. iv. Regression models could lead to substantially biased results compared to SWAT, there is a tradeoff between using regression and process-based models in estimating nitrate load. Results of this study provided critical insights for BMP cost-benefit and land use impact analysis for watershed management in Atlantic Canada.