Use of water isotope tracers to characterize the hydrology of prairie wetlands in Alberta, Canada

Abstract

Spanning 750,000 km2 across the Northern Great Plains of North America, the Prairie Potholes Region (PPR) is characterized by millions of shallow wetlands, forming a unique ecosystem that provides habitat for wildlife, carbon storage, and flood control. However, the presence and persistence of Prairie Pothole wetlands is vulnerable to the increasing effects of climate change and land use. Knowledge of northern Great Plains prairie wetland hydrology is based primarily on a few long-term research stations, but generalizing from these intensively monitored areas to the entire PPR requires application of synoptic hydrological approaches across a spatially extensive dataset. The aim of this study is to assess the relative importance of input water sources and evaporative water loss on prairie pothole wetlands of varying permanence class in the Parkland and Grassland Natural Regions in Alberta (Canada). We compare a normal precipitation year (2014) and a relatively dry year (2015), as well as comparing natural sites to 24 restored wetlands. Water samples were collected at intervals during May-August of both years and analyzed for oxygen and hydrogen isotope composition. A combination isotope-mass balance and Bayesian approach was used to generate hydrologic metrics including the isotope composition of input water and evaporation to inflow ratio. Temporal synchrony was tested among the years and site types. We observed little difference in wetland hydrology between the Grassland and Parkland during a normal climate year, but under drier conditions Grassland sites were more vulnerable to evaporation. High synchrony across the study regions indicates that climate change will likely affect wetlands similarly, while restored sites may be less vulnerable to drawdown than natural sites. Interestingly, restored wetlands were more resistant to drawdown than natural wetlands in the Parkland, which will have consequences for wetland biota and climate change adaptation in the northwestern PPR.