Evaluating Effects of Wetland Loss in the Souris River Watershed

About the study

Lead researcher: Pascal H. J. Badiou, Ph.D.

For this project we worked in the Souris River watershed. This is a large (61,100 km2), watershed of the Prairie Pothole Region (PPR). The Souris River originates in Saskatchewan, passes through North Dakota, and then crosses into Manitoba before joining the Assiniboine River. It is a hyper-eutrophic (high biological productivity) prairie watershed that has experienced dramatic increases in nutrient concentrations and is an important source of nutrients to the Assiniboine River and Lake Winnipeg. Within the Souris River watershed we focused on 9 sub-watersheds: three in Saskatchewan, (Antler River, Lightning Creek, and Pipestone Creek), three in North Dakota (Des Lacs River, Willow Creek, and Wintering River), and three in Manitoba (Elgin Creek, Graham Creek, and Medora Creek) spanning gradients of wetland cover and wetland drainage.

Timelines

The mapping and field components of this project were completed between 2014-2018. A final report was completed in 2019, and we continue to work with this data to explore the role of wetlands at scale with respect to mitigating non-point source nutrient pollution.

Goals & Purpose

The impact of agricultural drainage and resulting non-point source nutrient export on water quality has long been a concern across the entire PPR. In Canada, the three Prairie Provinces (Alberta, Manitoba, and Saskatchewan) are implementing surface water management strategies that have recognized the need for wetland restoration and conservation to help maintain and restore water quality and sustain watershed health. When this project began, unlike the US portion of the PPR, there was no complete wetland inventory for the Canadian portion of the Souris River watershed. This project contributed to the completion and harmonization of wetland inventories for the entire Souris River watershed and examined the link between current and historical wetland distribution and water quality.

Summary of Findings

• The proportion of intact wetlands across the SRB sub-watersheds is highly correlated with the proportion of perennial cover and inversely correlated to the proportion of cropland.
• The proportion of routed wetlands calculated based on change detection was highly correlated with increases in effective contributing area at the sub-watershed scale.
• Trend analyses for the nine sub-watersheds indicate that while total annual precipitation has not significantly increased there has been a significant increase in total annual discharge and runoff ratios in sub-watersheds that experienced high rates of wetland loss and had a lower ratio of intact to routed wetlands as fraction of their catchment areas.
• As wetland cover increases, phosphorus export and water yield both decrease substantially.
• Scaling up our results to the entire SRB and assuming that wetland loss has resulted in an increase in runoff ratios of 2% suggests that up to an additional 162 tonnes of P is exported out of the SRB in years with high runoff as a result of wetland drainage.