USGS Studies Help Restore the Chesapeake Bay

By Scott Phillips

The Chesapeake Bay, the Nation's largest estuary, has historically supported one of the most productive fisheries in the world, and the Bay's watershed provides vital habitat for migratory birds using the Atlantic Flyway. Unfortunately, the commercial, economic, and recreational value of the bay and its watershed has been degraded by poor water quality, loss of habitat, and over-harvesting of living resources. The restoration of the Bay and its watershed is overseen by the Chesapeake Bay Program (CBP), which is a partnership between Maryland, Virginia, Pennsylvania, the District of Columbia, Federal Government agencies (including USGS, FWS, and NPS), and the Chesapeake Bay Commission. While progress has been made, the CBP has recognized the need for enhanced restoration efforts and completed "Chesapeake 2000," a new agreement that revises and establishes new restoration goals for the next 10 years in the bay and its watershed. The USGS has the critical role of providing accurate, unbiased scientific information that is used to help formulate, implement, and assess the effectiveness of restoration goals in the Bay and its watershed. The success of the USGS Chesapeake Bay studies depends on the coordination of multiple USGS programs that have a scientific interest in the bay restoration. Over 40 USGS scientists located in offices throughout the bay watershed and at the CBP are involved in scientific investigations and information dissemination.

Results from the USGS Chesapeake Bay studies are used for important policy decisions related to DOI resources. These decisions include restoration of water-quality conditions to support fisheries and vital habitat, protection of DOI wetlands and lands, and assessing the factors causing the decline of waterfowl populations and other important wildlife species.

Restoring Dissolved-Oxygen Conditions for Fisheries
Low dissolved-oxygen levels in Chesapeake Bay have resulted in fish kills over the last several decades. The Bay includes several species considered DOI "trust resources," including American shad, striped bass, Atlantic sturgeon, and shortnose sturgeon. Nutrient-reduction actions began to be implemented by the CBP in the mid-1980s to improve dissolved-oxygen levels in the Bay. However, USGS streamflow and water-quality monitoring data indicated very slow improvement of nutrient levels in many of the major rivers entering the bay. USGS studies revealed the slow improvement in the rivers was due to changes in stream flow, lack of sufficient nutrient-source reductions, and the influence of watershed characteristics including the slow movement of nitrogen through ground water. Due to the slow improvements in water quality, the Bay was listed an impaired water body in 1999 under the Clean Water Act. The CBP began to further analyze the criteria needed to support fisheries and the restoration strategies needed to ensure more viable improvements to the bay's water quality.

In 2003, the CBP published the dissolved-oxygen criteria needed to protect and restore fisheries in the bay. The criteria were based partially on USGS studies of long-term changes in dissolved oxygen in the bay that showed the conditions have greatly degraded since the 1970's but that some areas of the bay have had low dissolved oxygen for several hundred years because of the natural characteristics affecting the bay. The CBP used the dissolved-oxygen criterion to determine a nutrient-load target of 175 million pounds of nitrogen that must be reached by 2010, a reduction of roughly 40 percent from current levels. The target was used to develop nutrient "allocations" for all the six states in the watershed. The states are in the process of developing and implementing management plans to meet the nutrient allocations. The USGS has also developed information on the nutrient sources and trends in the watershed to help the States develop the nutrient-reduction plans.

Restoration of Underwater Grasses
Underwater grasses, known as submerged aquatic vegetation (SAV), provide critical food for waterfowl populations that are managed by the Fish and Wildlife Service. SAV in the Chesapeake Bay, which is in the heart of the Atlantic Flyway, has declined greatly over the past three decades. Much of the SAV decline is linked to poor water clarity due to a combination of too much sediment and algal blooms, which are triggered by excess nutrients. USGS research has identified the water-clarity conditions needed for SAV to grow in different areas of the bay. The CBP, in conjunction with the FWS, has used the research to set water-clarity criteria that must be met in different parts of the bay. The criteria are providing the basis for a new restoration goal to almost double the amount of SAV in the bay by 2012. Further USGS studies revealed that sediment is the primary factor affecting water clarity in many parts of the bay. The CBP then began to develop sediment reduction strategies to improve water clarity. In support of this effort, USGS synthesized scientific information related to sediment rates, evaluated the relative contribution of sediment from different sources (rivers, shoreline/wetland erosion, and the ocean), documented the impact of altered sedimentation rates and patterns on estuarine biota, and began to develop models of sediment transport and deposition within the bay. These efforts will help provide the critical information needed to develop and implement sediment-reduction strategies.

Wetland Loss and DOI Lands
Wetland loss has occurred in many areas of Chesapeake Bay including lands that are part of the FWS National Refuge System. The wetland loss, due to land-use change and sea-level rise, is impacting populations of waterfowl and other species. The USGS is conducting several studies related to wetland loss and restoration. A study to document and predict the amount of impact of sea-level rise on wetland loss was conducted at the Blackwater National Wildlife Refuge. Monitoring of sedimentation rates continues at Blackwater. The FWS is using the information to develop a habitat-restoration plan and associated actions for the wetlands. Sea-level rise has also caused the loss of islands that are important habitat for waterbirds. The U.S. Army Corps of Engineers is constructing islands with dredge material, and the USGS is providing monitoring and analysis of selected species. The information will be used to help guide modification of habitat being constructed at Poplar Island. The USGS is also monitoring the vegetation, soils, birds, and other organisms to assess the success of a Corps of Engineers project to build a reconstructed freshwater wetland in the Anacostia River basin, Washington D.C.

Understanding the Threats to Waterfowl and Other Species
Waterfowl and fisheries populations have fluctuated in the bay due to poor water quality, impacts of contaminants and pathogens, loss of habitat, and over-harvesting. The USGS has conducted several studies to help determine some of the factors affecting these vital populations. The USGS has developed the Contaminant Exposure and Effects--Terrestrial Vertebrates database (CEE-TV) to help examine the condition of biota and coastal habitat. Information in the database has revealed that some wildlife populations in the bay watershed, such as osprey, have rebounded since the bans on DDT and associated contaminants were put into place. Other populations of waterfowl have declined due to loss of SAV and other food sources in the bay. Finally, the health of striped bass (rockfish), a species that is considered a DOI "trust resource," in the Chesapeake Bay is of national concern given the bay is the spawning grounds for 70-90 percent of the striped bass in the Atlantic Ocean. Populations of striped bass and other species have exhibited internal and external lesions that indicate poor fish health. The USGS organized a comprehensive sampling of striped bass in 2003, in cooperation with the FWS and several institutions in Maryland and Virginia. The results of the sampling found that a bacterial disease (mycobacteriosis) is affecting 50-70 percent of striped bass in 4 tributaries of the bay. The FWS and State agencies have set up a "striped bass task force" to begin to develop management alternatives based on this and future studies.

The efforts described above, in partnership with the CBP, FWS, and other concerned parties, will help provide the scientific foundation needed for lasting restoration of the Nation's largest estuary, the Chesapeake Bay. For more information, visit http://chesapeake.usgs.gov