Climate change impacts on freshwater wetland hydrology and vegetation cover cycling along a regional aridity gradient

Authors: Fay, Philip; GUNTENSPERGEN, GLENN - Us Geological Survey (USGS); OLKER, JENNIFER - University Of Minnesota; JOHNSON, CARTER - South Dakota State University

Submitted to: Ecosphere
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/18/2016
Publication Date: 10/15/2016
Publication URL: http://handle.nal.usda.gov/10113/5729141
Citation: Fay, P.A., Guntenspergen, G.R., Olker, J.H., Johnson, C. 2016. Climate change impacts on freshwater wetland hydrology and vegetation cover cycling along a regional aridity gradient. Ecosphere. 7(10):e01504. doi:10.1002/ecs2.1504.

Interpretive Summary: Global mean temperature may increase up to 6°C by the end of this century and together with precipitation change may steepen regional aridity gradients. The depth, persistence, and productivity of freshwater wetlands is tightly coupled to aridity, and the wetland in the northern Central Plains grasslands of North America provide critical breeding habitat for waterfowl and amphibians, support diverse grassland plant populations, and sequester carbon, but they are disappearing because of warming and the expansion of row crop agriculture. We applied the Wetlandscape model to simulate changes in the persistence of wetlands caused by warming, drought, and precipitation surplus at 19 locations across the Prairie Pothole Region of North America. The response of wetlands to climate changes depended on whether water deficits increased or decreased. Warming and 20% lower annual precipitation increased wetland water deficit, and at wetter locations strongly reduced wetland depth and duration on the landscape, but caused little affect in drier locations. Reduced water depths in wetter locations increased the productivity of the deepest class of wetlands. In contrast, 20% higher annual precipitation increased wetland depth and duration at dry locations where losses to warming have been greatest, but caused the deepest class of wetlands in wet locations to transition to become low-productivity lakes, reducing their quality as breeding habitat. Climate changes in general narrowed the range of favorable aridity for wetlands. Conservation strategies to mitigate potential negative effects of climate change on freshwater wetland ecosystems should focus on maintaining grassland habitat across the northern Great Plains, restoration of wetland complexes in wetter areas where losses to agriculture have been greatest and climate changes are likely to improve wetland productivity and habitat quality.

Technical Abstract: Global mean temperature may increase up to 6°C by the end of this century and together with precipitation change may steepen regional aridity gradients, impacting the hydrology, productivity, diversity, and ecosystem goods and services from freshwater wetlands, where the water balance is tightly coupled to water deficit. We applied the Wetlandscape model to simulate to simulate the precipitation and temperature sensitivity of the hydrology and vegetation dynamics of wetland complexes. Simulations were run for 63 precipitation x temperature combinations spanning 6°C warming and -20% to +20% precipitation change at 19 locations across an aridity gradient in the Prairie Pothole Region of North America. Aridity explained up to 95% of the variation in climate sensitivity of wetland stage and hydroperiod for temporary, seasonal, and semi-permanent wetlands. Climate sensitivities of stage and hydroperiod responded to climate changes as expected. Precipitation sensitivity and temperature sensitivity were increased at low aridity by 6°C warming and 20% less precipitation, most notably in semi-permanent wetlands, and declined with increasing aridity. Similarly, temperature sensitivity of stage and hydroperiod with 20% more precipitation increased at high aridity because of increased depth and hydroperiod in historically shallow wetlands. Aridity explained 60 – 73% of the variation in climate sensitivity of the cover cycle index (CCI), a measure of productivity in semi-permanent wetlands. Warming to 6°C increased the precipitation sensitivity of CCI at low aridity, but unexpectedly, 20% less precipitation increased the temperature sensitivity of CCI at high aridity, because the reduced depth reduced CCI at most locations. 20% more precipitation amplified CCI temperature sensitivity near its historic peak aridity. The response of wetland complexes to climate changes thus depends on whether water deficits increase, benefitting wetlands at low aridity, or decrease, benefitting wetlands at high aridity, but likely include a narrowing of favorable ranges for all wetland permanence types. Conservation strategies to mitigate potential deleterious effects of climate change on freshwater wetland ecosystems need to account for variation in response along regional aridity gradients.