Implications of waterfowl impoundments as a response to sea-level driven saltwater intrusion

Coastal landscapes have been modified for centuries to facilitate the expansion of agriculture, aquaculture, and infrastructure, and now include extensive anthropogenic land uses in areas that are predicted to convert to wetlands with sea-level rise. In the Chesapeake Bay, impoundments are commonly constructed on low-lying, salt-impacted farmland and residential property to create shallow water habitat for waterfowl. There are no public records of privately-owned waterfowl impoundments, and the small size of the earthen containment berms and dense vegetation cover make them difficult to detect from satellite imagery. In this study, we trained a convolutional neural network-based deep learning model using high resolution (1 m) topobathymetric data to detect impoundments across the Chesapeake Bay region. The model detected 1684 impoundments with a total spatial extent of 6.6 km² (1627 acres). We found that the number of impoundments constructed on the Eastern Shore of Maryland increased substantially after the establishment of the Conservation Reserve Enhancement Program in 1997. Several federal-state programs now exist which provide landowners with incentives to create shallow water habitat on environmentally sensitive agricultural land. The majority of detected impoundments (60%) are located within the marsh migration pathway under 1 m of sea-level rise, suggesting that current federal and state programs may unintentionally incentivize construction of barriers to marsh migration.