Effects of subsurface soil characteristics on depressional wetland inundation within the Coastal Plain of the Chesapeake Bay watershed

Authors: LEE, S. - University Of Maryland; McCarty, Gregory; Moglen, Glenn; LANG, M.W. - Us Fish And Wildlife Service; Sadeghi, Ali; Green, Timothy; YEO, I.Y. - Newcastle University; RABENHORST, M. - University Of Maryland

Submitted to: Hydrological Processes
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/1/2018
Publication Date: 11/6/2018
Citation: Lee, S., McCarty, G.W., Moglen, G.E., Lang, M., Sadeghi, A.M., Green, T.R., Yeo, I., Rabenhorst, M. 2018. Effects of subsurface soil characteristics on depressional wetland inundation within the Coastal Plain of the Chesapeake Bay watershed. Hydrological Processes. 33(2):305-315. https://doi.org/10.1002/hyp.13326.
DOI: https://doi.org/10.1002/hyp.13326

Interpretive Summary: Wetlands are commonly found on the Coastal Plain of the Chesapeake Bay watershed. They act as a key natural system to maintain the overall health of Coastal Plain ecosystems. Water cycling between wetlands and surrounding areas has not been fully studied in this region due to a lack of data. To protect and assess wetland benefits, multiple sensors have been recently installed in this region, which provides a chance to improve our understanding of the role of wetlands in the landscape. This study investigated how wetland hydrologic patterns differ by soil characteristics. We compared observed surface and groundwater data between the sites with distinctive soil drainage characteristics. A wetland located in soils with a semi-impervious layer showed inconsistent patterns between surface and groundwater over the monitoring period, indicating limited connectivity between surface and groundwater. In contrast, a wetland located in soils with high infiltration potential showed strong hydrologic interactions between surface water and groundwater. Thus, subsurface soil characteristics were found to exert substantial impacts on the dynamics of wetland hydrology.

Technical Abstract: Depressional wetlands on the Coastal Plain of the Chesapeake Bay watershed (CBW) have been examined to evaluate their ecosystem functions. However, effects from subsurface soil characteristics on wetland hydrology remain largely unknown due to the difficulty of monitoring water levels beneath the land surface. The objective of this study is to examine groundwater contribution to depressional wetland hydrology on two sites with different soil hydraulic characteristics. A well and piezometer were co-installed at the lowest point of each wetland to monitor surface water level (SWL) and groundwater level (GWL), respectively. The site with a low-permeability soil layer demonstrated different patterns in SWL and GWL dynamics over a monitoring period, while there was strong similarity in temporal dynamics between these two water levels observed at the site without a low-permeability soil layer. Limited vertical water movement in the site with a low-permeability soil layer isolated SWL from GWL. Accordingly, hydroperiod (i.e., duration of time for surface water inundation or saturation) of the wetland underlain by a low-permeability soil layer was less affected by groundwater compared to the wetland without a low-permeability soil layer. Cross-correlation time-series analysis also indicated a strong connection between SWL and GWL at Site #2, indicating a potential causal relationship with surface water flowing to groundwater. This conclusion is consistent with measurement of a constant downward hydraulic gradient at this site. These findings showed varying interactions between wetland surface and groundwater depending on underlying soil characteristics.