Mapping landscape-scale hydrological connectivity of headwater wetlands to downstream water: a catchment modelling approach - Part 2

Authors: YEO, I.Y. - University Of Newcastle; LEE, S. - University Of Maryland; LANG, M.W. - Us Fish And Wildlife Service; YETEMEN, O. - University Of Newcastle; McCarty, Gregory; Sadeghi, Ali; EVENSON, G.R. - Virginia Polytechnic Institution & State University

Submitted to: Science of the Total Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/16/2018
Publication Date: 12/15/2018
Citation: Yeo, I., Lee, S., Lang, M., Yetemen, O., McCarty, G.W., Sadeghi, A.M., Evenson, G. 2018. Mapping landscape-scale hydrological connectivity of headwater wetlands to downstream water: a catchment modelling approach - Part 2. Science of the Total Environment. 12/15/2018. https://doi.org/10.1016/j.scitotenv.2018.11.237.
DOI: https://doi.org/10.1016/j.scitotenv.2018.11.237

Interpretive Summary: Headwater wetlands have been shown to influence downstream water quality. However, many wetlands, because of being isolated without apparent connection to larger wetland systems, continue to be at risk and not protected by state and federal regulations. This model simulation study provided additional explanation and support that highlighted the connectivity and functioning of geographically isolated wetlands (GIWs). In other work, we showed the connectivity between hydroperiod and wetland function. This modeling exercise demonstrated that GIWs control the overall catchment water budget and the seasonal variations in water fluxes. This was done through a modification to the Soil and Water Assessment Tool (SWAT) to include wetland assessment capability (SWAT-WET). This model was applied to the Greensboro watershed, located in the Mid-Atlantic region of USA, and simulated hydrological processes at a daily time scale over 1985-2015 under two contrasting land use scenarios (i.e., with the presence and absence of GIWs). Model results revealed how GIWs influence the catchment water budget and the streamflow generation processes over the long run (30 years), inter-annually, and at monthly time scales. This modeling exercise provides important insights and support for the future management and protection of GIWs.

Technical Abstract: In Part 1 for this two-part manuscript series, we presented a rapid assessment method for mapping inundation of seasonal forested wetlands and quantifying their cumulative landscape-scale hydrological connectivity with downstream water. This study suggested strong hydrological coupling between geographically isolated wetlands (GIWs) and downstream water at the seasonal timescale via groundwater. As a followup, this paper investigates the hydrological connectivity of GIWs with downstream water and cumulative catchment-scale hydrological impacts over multiple time scales. Specific modifications improving representation of wetland processes were incorporated into Soil and Water Assessment Tool (SWAT). A version of SWAT with improved wetland function was applied to the Greensboro Watershed located in the Mid-Atlantic Region of USA and simulated hydrological processes at a daily time scale over 1985-2015 under two contrasting land use scenarios (i.e., the presence and absence of GIWs). The comparative analysis of simulation outputs elucidated how GIWs could influence the partitioning of precipitation between evapotranspiration and terrestrial water storage, recharge soils and groundwater, and affect water transport mechanism and routing processes that generate stream flow. The model results showed GIWs influenced catchment water budget and stream flow generation processes over the long-term, inter-annual, and monthly time scales. Through the hydrological continuum that GIWs created between surface water and groundwater, the study watershed increased terrestrial water storage during the wet season, which in turn supported wetlands and buffered the dynamics of shallow ground water during dry season. The inter-annual modelling analysis illustrated that densely distributed GIWs can exert strong hydrological influence on downstream water by regulating surface water runoff, while maintaining groundwater recharge and AET under changing (wetter) climate conditions. The study findings highlight the hydrological connectivity of GIWs with downstream waters and the cumulative hydrological influence of GIWs as hydrologic sources to downstream ecosystem through different runoff processes over multiple time spans.