Marsh expansion on the Delmarva farmlands: Can ongoing changes be a part of long-term land management?

Keywords: Saltwater intrusion, agriculture, marsh, spatial analysis, remote sensing, aerial image, satellite, machine learning, USA.
Abstract Type: Paper Abstract

Abstract

Saltwater intrusion (SWI) on coastal farmlands can change the soil chemistry and render it unusable for agricultural purposes. Globally, over a quarter of arable land is negatively impacted by soil salinization, including more than 50% of irrigated land. In addition to decline in crop health, increasing soil salinity might result in gradual conversion of farmlands to marsh. We quantified the area of farmlands that have converted into marsh across 14 coastal counties in the Delmarva Peninsula. We utilized very high-resolution (1 m) aerial imagery from the National Agriculture Imagery Program (NAIP) and seasonal information derived from the moderate resolution (30 m) Landsat satellite imagery collection. Using a Random Forest algorithm with 100 trees and over 87,520 reference points for training and testing, we developed high-resolution geospatial datasets for the study area for two time-steps: 2011-2013 and 2016-2017. We estimated that over 8,700 ha of farmlands converted to marsh across the counties between 2011 and 2017. The three Delaware counties have the largest share of such conversions at 4,473 ha, followed by the counties in Maryland (3,488 ha) and Virginia (784 ha). Our work provides evidence for an immediate policy attention required to protect the coastal lands against increasing soil salinization. While changing crop types that are more suitable for salt-impacted lands are being discussed as an adaptation strategy, another land management strategy might include a controlled conversion of these landscapes into marsh that can support wildlife or act as a barrier to encroaching seawater.