Surface Hydrologic Connectivity Between Delmarva Bay Wetlands and Nearby Streams Along a Gradient of Agricultural Alteration

Abstract

Although recent U.S. Supreme Court rulings indicate surface hydrologic connectivity (SHC) between geographically isolated wetlands and nearby streams may be used, in part, to determine wetland jurisdictional status, and ecologic implications are considerable regardless of policies, wetland–stream SHC has rarely been quantified. Furthermore, the impact of cultivation and restoration on wetland–stream SHC is largely unknown. To help fill these knowledge gaps, we recorded SHC patterns during water year 2010 in non-perennial streams connecting Delmarva bay wetlands, which are commonly considered geographically isolated, and nearby perennial streams. We also evaluated how hydrologic wetland restoration impacts SHC relative to historical wetlands and native forested wetlands. Cumulative connection duration, number of connectivity transitions, mean connection duration, and maximum individual connection duration (D max-c ) were quantified. Forested wetlands were connected to perennial streams for a greater cumulative duration but exhibited fewer connectivity transitions relative to both historical and restored wetlands. SHC between historical and restored wetlands and nearby perennial streams did not differ with respect to any of the calculated metrics. Forested wetland-stream SHC was seasonally intermittent, exhibiting stream outflow from mid-fall to late-spring during periods of low evapotranspiration and elevated groundwater levels but lacking connectivity during summer months when evapotranspiration and groundwater were at an annual high and low, respectively. Historical and restored wetland-stream SHC was largely ephemeral, occurring in response to antecedent rainfall, particularly during winter and spring. Stepwise regression models describe cumulative connection duration and D max-c as a function of wetland, watershed, and non-perennial stream metrics including watershed relief, non-perennial stream slope, non-perennial stream length, and soil saturated hydraulic conductivity. Wetland–stream SHC has potential ecological implications, including provision of dispersal corridors for biota, biogeochemical processing of nutrients, and downstream delivery of energy, matter, and organisms, and is currently tied to wetland regulatory status in the U.S.