Marsh Loss in Nanticoke Estuary, Chesapeake Bay

Abstract

Marsh loss in the Nanticoke estuary dates from the 1920s. Since 1938 overall rate of loss has averaged 49.6 ha annually, with rates increasing down estuary. Most losses have occurred in submerged upland marshes; tidal freshwater marshes are stable. Interior ponding has been the primary mechanism of loss. Rising water levels are postulated to be the underlying force behind marsh losses in this estuary. R ECENT predictions of accelerated rates of sea-level rise in the next century because of anthropogenic greenhouse warming of the atmosphere have renewed concern about increased coastal erosion and land loss. The immediate threat is greatest for coastal marshes, where vertical accretion rates are outstripped by local sea-level rise. The ominous consequences faced by coastal marshes from a rapidly rising sea level are best exemplified in the Mississippi delta, where local rates of submergence, largely from subsidence, are approximately 1 cm annually. Particularly evident is the rapidity of the primary mechanism of marsh loss, which consists of interior-pond formation, coalescence, and enlargement. Elsewhere along the Gulf and Atlantic coasts of the United States, documentation of rates and processes of marsh loss is more sketchy. Most of the reported losses are local, involving creek-bank erosion, formation of rotten spots, and shoreline-cliff retreat. To date, extensive marsh loss from interior ponding has been reported only for the Blackwater Wildlife Refuge on the Eastern Shore of Maryland (Stevenson, Ward, and Kearney 1986), where approximately one-half of the upland marshes have been lost since 1938. The extent of interior ponding and other mechanisms of marsh loss in other marsh types of Chesapeake Bay is unknown. The research reported in this article was undertaken to assess the broad importance of interior ponding and other processes in marsh types of the Nanticoke River, a representative marsh-dominated estuary of Chesapeake Bay. The Nanticoke River is one of the largest estuarine tributaries on the Eastern Shore. The stream meanders almost