U.S. Geological Survey Home Page USGS Patuxent Wildlife Research Center Science Meetings; dedicated to Chandler S. Robbins USGS Patuxent Wildlife Research Center; Science Meetings dedicated to Chandler S. Robbins Dedicated to Chan Robbins USGS Patuxent Wildlife Research Center; Science Meetings dedicated to Chandler S. Robbins Poster Abstracts from USGS Patuxent Wildlife Research Science Meetings, October, 2006
Patuxent Science Meeting 2006 Poster Abstract

Deterioration of a Mid-Atlantic coastal marsh

Soeder DJ, Birch DL (FWS)

Blackwater National Wildlife Refuge was established in 1933 as a way-station for migratory

birds along nearly the entire reach of the Blackwater River in Dorchester County, on Maryland's

Eastern Shore. The 26,000-acre refuge is composed mainly of Chesapeake Bay tidal marsh,

characterized by fluctuating water levels and salinity gradients. Deterioration and loss of

marshland and forested wetlands at the refuge is significant. Aerial photographs from 1938

show a relatively intact marsh along the Blackwater River with only a few small ponds. By

1985, however, the marsh had degraded into large tracts of open water, and current wetland

losses are estimated at 7,000 to 8,000 acres. Contributing factors may include rising sea level,

invasive species such as nutria (Myocastor coypus), degraded water quality, and human

activities, although the relative impacts of these are poorly understood. Observations show that

erosion of the marsh is occurring at a rapid rate, and vertical accretion is not keeping pace with

sea-level rise. Research indicates that restricted tidal exchange within the marsh may be a

critical factor, with impounded water causing deterioration of the largely organic, peat-rich

substrate through the action of trapped sulfides, low dissolved oxygen, build-up of nutrients, or

some combination of factors. Saltwater intrusion into formerly freshwater areas due to marsh

deterioration at a watershed divide, and plans for the construction of several large housing

developments within a tributary watershed are but two of several issues of concern to the refuge

management. Better hydrologic characterization of the marsh is needed to help understand the

impacts of these and other problems at the refuge. Precise tidal-stage data, salinity

measurements, streamflow, ground-water and water-quality analyses have all been proposed,

along with LIDAR elevation studies, sediment accretion measurements, and substrate coring to

achieve a better understanding of the physical, geological, geochemical, and hydrologic

processes operating in the marsh. The effectiveness of any planned restoration may be

dependent upon the knowledge of marsh hydrology and the underlying causes of wetland loss,

neither of which are currently well understood. The time frame for such studies may be short,

however; one proposal under consideration will re-build the marsh by adding dredge spoils from

Baltimore Harbor at the rate of 30 million tons per year over 10 years. The problems of

Blackwater are relevant to wetland science in the neighboring Delaware Estuary, because the

fringe marshes there are facing similar threats. Land-use changes, pressure from real estate

development, habitat loss, degraded water quality, invasive species, and rising sea levels are

issues in the Delaware Estuary as well as in the Chesapeake Bay. The pressure to dredge and

to use the dredge spoils in a constructive manner has also been a concern in the Delaware

Estuary. The applicable issue from Blackwater is that the performance of a wetland "restored"

Friday, September 22, 2006

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