The use of riparian health assessments to assess cumulative anthropogenic effects to wetlands in the Prairie Pothole Region of Saskatchewan

Abstract

Wetlands are significant contributors to global biodiversity, supporting disproportionately high numbers of species relative to their area. Riparian areas associated with wetlands provide many services that are both ecologically and economically important, such as groundwater recharge, sediment capture and shoreline stabilization, flood mitigation, nutrient processing, increased water quality, carbon sequestration, and essential habitat for wildlife. Agricultural activity has resulted in the drainage or modification of between 40-70% of wetland basins within the Prairie Pothole Region of the northern Great Plains. The impacts of human activity on the remaining wetlands are difficult to estimate and there is no one optimal indicator or assessment method that is applicable to all regions or situations. Locally developed riparian health assessments, designed to evaluate wetland function under different grazing regimes, are cost-effective with the potential for broader use in wetland environmental assessment, monitoring, and management or restoration activities. In this study I investigated the hypothesis that riparian health assessments can distinguish between wetlands in five categories of land use that represent different levels of anthropogenic modification: ungrazed cultivated cropland, ungrazed native grassland, grazed native grassland, ungrazed tame perennial forage, and grazed tame perennial forage. Noting that current riparian health assessment protocols lack a community composition component other than the presence and distribution of invasive and disturbance species, I also sampled plant species frequency at each of my study sites. I found that wetlands in cultivated croplands had significantly lower riparian health scores than wetlands in both tame and native grasslands. Among tame and native sites, grazing status was more important than upland cover type in determining wetland health, with grazed wetlands receiving significantly lower scores than their ungrazed counterparts. Despite their functional similarity to wetlands within native grasslands, species composition of wetlands within ungrazed tame perennial forage more closely resembled that of wetlands in cultivated uplands. Although grazing negatively affected riparian ground cover and soil stability, it significantly reduced both the overall cover and distribution of invasive plant species along wetland reaches. These results suggest that upland revegetation and restoration of function to degraded wetlands is not necessarily followed by re-establishment of original riparian species composition. If biodiversity is a desired outcome of wetland restoration efforts, additional measures must be taken to enable the establishment and persistence of preferred plant species.