Abstract
The hydrology of seasonally inundated depression wetlands can be highly sensitive to climatic fluctuations. Hydroperiod—the number of days per year that a wetland is inundated—is often of primary ecological importance in these systems and can vary interannually depending on climate conditions. In this study we re-examined an existing hydrologic model to simulate daily water levels in Sinking Pond, a 35-hectare seasonally inundated karst-depression wetland in Tennessee, USA. We recalibrated the model using 22 years of climate and water-level observations and used the recalibrated model to reconstruct (hindcast) daily water levels over a 165-year period from 1855 to 2019. A trend analysis of the climatic data and reconstructed water levels over the hindcasting period indicated substantial increases in pond hydroperiod over time, apparently related to increasing regional precipitation. Wetland hydroperiod increased on average by 5.9 days per decade between 1920 and 2019, with a breakpoint around the year 1970. Hydroperiod changes of this magnitude may have profound consequences for wetland ecology, such as a transition from a forested wetland to a mostly open-water pond at the Sinking Pond site. More broadly, this study illustrates the needs for robust hydrologic models of depression wetlands and for consideration of model transferability in time (i.e., hindcasting and forecasting) under non-stationary hydroclimatic conditions. As climate change is expected to influence water cycles, hydrologic processes, and wetland ecohydrology in the coming decades, hydrologic model projections may become increasingly important to detect, anticipate, and potentially mitigate ecological impacts in depression wetland ecosystems.
Highlights
Isolated depression wetlands—such as vernal pools, Carolina bays, playas, and karst sinkhole wetlands— provide important habitats to plant and animal species and support regional biodiversity
To complement root mean-squared error (RMSE) and Nash-Sutcliffe Efficiency (NSE), we developed a third metric, which we refer to as hydroperiod discrepancy (HPD), to represent the degree to which the calibrated model overpredicted (HPD > 0) or underpredicted (HPD < 0) pond hydroperiod
To check whether trends in the precipitation records used in the Sinking Pond hydrologic model were consistent or discrepant with larger regional patterns of precipitation trends, we obtained precipitation records from National Centers for Environmental Information (2020) for all NCEI weather stations located within 100 km of the Sinking Pond study site having at least 70 years of annual precipitation data between 1920 and 2019, which yielded 8 weather stations (Online Resource 3)
Summary
Isolated depression wetlands—such as vernal pools, Carolina bays, playas, and karst sinkhole wetlands— provide important habitats to plant and animal species and support regional biodiversity. Such depression wetlands may be increasingly vulnerable to anthropogenic climate and landcover change and to human demands on water resources (Tiner 2003; Wolfe et al 2004; Gómez-Rodríguez et al 2010; Bird and Day 2014; Bolpagni et al 2019; Cartwright 2019). Many small depression wetlands are William J. Wolfe is retired from Lower Mississippi-Gulf Water Science Center, U.S Geological Survey, Nashville, TN, 37211, USA
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