Name
Impacts of managed dike realignment on soils and shallow groundwater
Description
Coastal defense structures (e.g. dikes, seawalls) protect vulnerable communities along marine coastlines and estuaries from the physical and chemical influences of adjacent water bodies. However, these structures are susceptible to overtopping or breaching by tides and waves potentially amplified by climate change induced sea level rise. Repeated inundation by salinized water can contaminate freshwater resources and salinize soil, impacting land use activities including agricultural productivity. Managed ecosystem-based dike realignment approaches and salt marsh restoration can provide alternatives to traditional mitigation approaches; however, these strategies often sacrifice coastal land to marine influence following flooding. Here, we assess the changes to soil salinity at a managed dike realignment project prior to the transformation from diked agricultural land to an estuarine environment. Geophysical surveys, soil/sediment sampling, and soil moisture monitoring were used to compare baseline data collected before the realignment, and then during 8-10 months of intermittent flooding (i.e., spring tides every two weeks). The formerly freshwater environment (bulk electrical conductivity ~200 µs/cm) was shown to transform into a moderately saline environment (~6000 µs/cm) following less than twenty flood events, and sediment deposition occurred at high rates with up to 4 cm of sediment deposited per flood. The realignment zone serves as an engineered analog of coastal flooding, presenting an opportunity to examine the impacts of salinized water on agricultural soils expected in future. Results demonstrate that a small number of flooding events by even moderately saline water can cause root zone salinization and critically reduce crop productivity in coastal areas.