Seasonal drivers of geographically isolated wetland hydrology in a low-gradient, Coastal Plain landscape

Authors: LEE, S. - University Of Maryland; McCarty, Gregory; Moglen, Glenn; LANG, M.W. - Us Fish And Wildlife Service; JONES, C,N. - University Of Maryland; PALMER, M. - University Of Maryland; YEO, I.Y - University Of Newcastle; Anderson, Martha; Sadeghi, Ali; RABENHORST, M. - University Of Maryland

Submitted to: Journal of Hydrology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/20/2020
Publication Date: 1/24/2020
Citation: Lee, S., McCarty, G.W., Moglen, G.E., Lang, M., Jones, C., Palmer, M., Yeo, I., Anderson, M.C., Sadeghi, A.M., Rabenhorst, M. 2020. Seasonal drivers of geographically isolated wetland hydrology in a low-gradient, Coastal Plain landscape. Journal of Hydrology. https://doi.org/10.1016/j.jhydrol.2020.124608.
DOI: https://doi.org/10.1016/j.jhydrol.2020.124608

Interpretive Summary: The identification of hydrological connectivity of depressional wetlands to downstream water resources is critical for better management and protection of such wetlands within larger ecosystems. Numerous studies have been conducted to demonstrate this hydrologic connectivity, but most of these studies were limited to the use of hydrologic modeling and were focused only on surface water connections. Due to the strong influence of surface water connections, temporal dynamics between wetlands and downstream waters remained poorly understood. This study uses in-situ observations of surface and groundwater level changes to provide explicit evidence for hydrologic connectivity of depressional wetlands with downstream waters through groundwater. Results showed that temporal variations of surface water level and groundwater level of depressional wetlands were highly consistent with downstream baseflow measurements over the monitoring period. Statistical analyses indicated a strong connection between depressional wetlands and downstream baseflow with the model, accounting for 69 to 91 percent of the observed variation. These results highlight the hydrological and biochemical functions of depressional wetlands. This study supports the value of ongoing wetland conservation practices and the importance of wetland protection plans.

Technical Abstract: Numerous studies have been conducted to demonstrate hydrologic connectivity of depressional wetlands with downstream waters for legal protection of these wetlands. Quantifiable or measurable connections have been found mostly by hydrologic modelling or remote sensing approaches. However, there have been few studies using in-situ observations and results from these studies were generally limited to surface water connections. Due to high temporal constrain in surface water connections, temporal dynamics between wetlands and downstream waters remained poorly understood. This study uses in-situ observations to provide explicit evidence for hydrologic connectivity of depressional wetlands with downstream waters through groundwater on the Coastal Plain of the Chesapeake Bay watershed. Surface water level (SWL) and groundwater level (GWL) of two depressional wetlands were monitored using a well and piezometer, respectively. SWL and GWL were compared with streamflow collected at the outlet of the drainage area where the two depressional wetlands exist. Focusing on the groundwater connection, baseflow derived from streamflow was analyzed with wetland water levels. We further estimated wetland hydroperiod to examine the carbon storage function based on the relationship between hydroperiod and decomposition rate. Our in-situ observations showed that SWL and GWL of depressional wetlands were strongly related with downstream baseflow. Furthermore, temporal dynamics between wetland water levels (SWL and GWL) and downstream baseflow indicated high consistency as well as significant relationships with coefficients of determination (R2) of 0.69 – 0.91. Predicted carbon storage function of depressional wetlands indicated that a wetland with a longer hydroperiod was more effective to hold carbon compared to the one with a shorter hydroperiod. Our analyses verified the strong groundwater connection between depressional wetlands and downstream baseflow.