Depressional Wetlands in South Georgia, USA: Will Filling Ditches Restore Function?

Wetlands comprise approximately 6% of the Earths land surface, yet support a disproportionate amount of ecosystem services including high biodiversity. Throughout southern Georgia, USA historic drainage ditches altered hydrologic periods that persist today and affect wetland functions, particularly as wildlife habitat for amphibians. While it is clear that drainage ditches alter critical hydrology, it is less clear whether simply filling ditches will restore wetland function. We are studying six depressional wetlands at the Alapaha River WMA, all of which have altered hydrology and three of which will undergo filling of historic ditches in late 2021. Here we report the initial one-year of monitoring data that will enable us to compare how ditch filling influences wetland hydroperiods and the priority amphibians that depend on them. We used electromagnetic induction to map horizontal soil moisture variation spatially in each wetland, which indicate a moister drainage channel in most cases. Electrical resistivity was used to map moisture variation vertically which demonstrated both perched (above 2 m) and deep (~15m) water tables. Soil clay concentration in 40 to 220 cm are high (up to 50%) in wetlands with depth to clay increasing outside the wetlands. Shallow wells (2.5 m) in all wetlands indicated long periods (>6 months) of perched water during 2020/21 with saturated soil moisture (volumetric water content >0.4 cm3 cm-3) and reducing conditions (<-400 mV). During some resistivity measurements water was draining away from the wetland. Current monitoring in these six wetlands suggests a good pairing and we expect future ditch filling to raise water levels and extend periods of saturation.