Role of Meteorological Controls on the Inter-annual Groundwater Dynamics of Wetlands in a Southeastern US Watershed

Abstract:

Wetlands are highly valued for their numerous ecological services including water quality improvement and land-atmosphere interactions. The effectiveness of wetlands in delivering these services is strongly influenced by the shallow groundwater dynamics. As such, in order to understand the variation of ecological processes in wetlands, it is crucial to first quantify the controls on the temporal variations in the groundwater table. In this paper, a physically based and fully distributed hydrologic model was applied to simulate the long term variation of groundwater and the distribution of wetlands in the Second Creek watershed. Covariation in simulated groundwater table and meteorological variables were analyzed using Bayesian regression to evaluate the integrated role of seasonal meteorological controls on interannual variations in maximum groundwater height and the start date and length of the wet period (defined as the period when the groundwater depth is shallower than 30cm). The meteorological controls were quantified based on the Palmer Drought Severity Index (PDSI), which is an indicator of net wet or dry recharge period. Results indicate that the PDSI in autumn and spring is the dominant control on the length of wet time. The start date of wet time in downstream wetlands is controlled by the autumn PDSI while that in headwater wetlands is controlled by the PDSI in both autumn and the previous summer. The maximum groundwater table height inundation depth of wetlands is controlled by the winter PDSI. These results highlight that to understand that susceptibility of a given groundwater dynamics characteristic, one needs to track the corresponding changes in meteorological forcings within particular seasons. Results will help understand and predict anticipated changes in groundwater dynamics and ecological processes of wetlands in response to changes in meteorological forcings due to climate change in the southeastern U.S.