Modeling of nutrient export and effects of management practices in a cold-climate prairie watershed: Assiniboine River watershed, Canada

Non-point source pollution due to agricultural activities is an important problem that has been threatening water resources in Canadian prairie watersheds. The development of strategies to prevent nutrient loss depends on the quantification of nutrient mobilization and transport across a watershed. Integrated eco-hydrological models can play an important role in this regard. However, current model applicability to cold-climate Canadian prairie watersheds is limited due to the complex dynamics of nutrient export under the existence of numerous landscape depressions and freeze-thaw cycles. The aim of this study was to evaluate an eco-hydrological model for nutrient export prediction and assess the impacts of management practices for a cold-climate prairie watershed. To achieve the objectives, a new version of the SWAT model called SWAT-PDLD, which combines SWAT and a Probability Distributed Landscape Depressions (PDLD) model, along with a seasonally varying soil erodibility factor, was applied to a Canadian prairie watershed (the Assiniboine River watershed, Saskatchewan, Canada). The PDLD module is used to simulate the effect of the numerous landscape depressions that exist in these watersheds on streamflow, whereas a seasonally varying soil erodibility factor is used to take into account seasonal variation of sediment and nutrient generation due to the cold climate conditions. Model calibration and uncertainty analysis were performed using the Sequential Uncertainty FItting (SUFI-2). The study shows that the SWAT-PDLD model with seasonally varying soil erodibility simulates the daily nutrient export in a cold prairie watershed satisfactorily as confirmed by both graphical plots and statistical measures. A sensitivity analysis of sub-watershed discretization revealed that the streamflow is relatively insensitive to sub-watershed discretization but it did affect sediment and nutrient export. Importantly, the model shows that both filter strips and cover crops decreased sediment, phosphorous, and nitrogen export, while conservation tillage increased phosphorous export in the study watershed.