The Prairie-Pothole Region of North America—a vast expanse of grasslands, or prairies, interspersed with shallow wetlands, or potholes—stretches across Iowa, Minnesota, and the Dakotas in the United States and north through Saskatchewan and Alberta in Canada. These wetland formations, left behind by receding glaciers thousands of years ago, are home to many animal species, including more than half of all migratory waterfowl in North America, and play a key role in controlling flooding by absorbing rain surges, snowmelt, and floodwaters.
The study of how wetlands interact with one another and other water systems is a thriving area of research, especially because it helps inform public policy. For example, the federal Clean Water Act is intended to protect the integrity of “navigable waters”; Clean Water Act regulatory protections have often been interpreted to apply specifically to those wetlands that may affect traditional navigable waters.
To better understand the relationship between wetlands and water flowing into streams, Brooks et al. zeroed in on the Pipestem Creek watershed in North Dakota. The team collected water samples over a 2-year period (2014–2015) in prairie-pothole wetlands and a nearby stream and compared them to data detected by NASA’s Landsat satellite over the same time period.
Chemical signatures left behind by hydrogen and oxygen isotopes during the evaporation process (called isotopic evaporation signals) allowed the researchers to trace back the water’s path. From this, they were able to estimate how much the wetlands collectively contribute to the stream’s flow, as well as how large the water’s surface area would need to be to generate such a signal. Their findings indicated that the wetlands near Pipestem Creek contribute to the stream’s flow throughout the summer and that sections of the stream occasionally become disconnected.
This study demonstrates an innovative new approach to estimating wetlands’ impact on surrounding aquatic systems and tracing the pathways of surface-level water and groundwater. By combining isotopic measurements of water samples collected in the field with satellite data and perhaps incorporating additional types of data, scientists can continue to build a richer understanding of wetland water systems—and hopefully help improve the management of these ecosystems. (Water Resources Research, https://doi.org/10.1002/2017WR021016, 2018)
—Sarah Witman, Freelance Writer