RESOURCES OF THE BAY 



The Chesapeake Bay provides a variety of re- 

 sources. The most obvious are commercial and 

 recreational fisheries for clams, oysters, blue crabs, 

 menhaden, striped bass (Moronc saxatilis) and 

 other species. Other resources are habitat for wild- 

 life and migratory birds, waste treatment, and 

 water of quality that is suitable for recreation. 



Each of these resources is dependent on the 

 ecological functions of the Bay system. One objec- 

 tive of these conceptual model diagrams is to indi- 

 cate the supporting biology for the various re- 

 sources. Many ecological processes involve loops or 

 cycles within the system, which are vulnerable to 

 disturbance at any point. 



WETLANDS 



The wetlands considered part of the Chesa- 

 peake Bay system are tidal mudflats and marshes 

 that experience tidal flushing (fig. 3). Most wet- 

 lands are above mean low water, but some emer- 

 gent wetlands extend to shallow (2 m) depths. 



Marshes can be divided into several types on 

 the basis of plant communities. Through their func- 

 tion as sediment traps and nutrient absorbers, mar- 

 shes play a role in maintaining water quality of the 

 Bay. Fresh- and brackish-water mixed vegetative 

 marsh communities, salt marsh cordgrass communi- 

 ties, and arrow-arum/pickerel weed communities 

 are the most valuable marsh types in terms of pro- 

 duction, habitat, and erosion buffering (Silberhorn 

 etal. 1974). 



Some marshes provide a spawning area for fish- 

 es, and marsh invertebrates serve as fish food (Wass 

 and Wright 1969). 



Marshes also provide food and habitat for mi- 

 gratory waterfowl, resident birds, and other wild- 

 life (Wass and Wright 1969). Migratory geese, 

 whistling swans, and ducks use adjacent farmlands, 

 as well as the marsh, as food sources during part of 

 the year (L. E. Cronin, pers. comm.). Herons, 

 egrets, and ibises nesting in the marshes arc impor- 

 tant consumers of fish and crustaceans. Gulls, 

 during the winter, and terns, during the summer, cat 

 fin- and shellfish in the marshes (R. Andrew, pers. 

 comm.) 



By feeding in farmlands and defecating in the 

 marsh, birds may import carbon and nutrients. The 

 magnitude of such imports is not known. Birds also 



export some material when they leave the marshes 

 to migrate. Results from studies of the role of birds 

 in other ecosystems suggest that the quantity of 

 carbon and nutrients cycled by migratory birds 

 during feeding and elimination within the system is 

 much greater than that of material imported to or 

 exported from the system. 



Mammals which use the marsh habitat include 

 nutria (Myocastor coypus), muskrat (Ondatra 

 zibcthica), mink (Mustcla vison), and raccoon 

 (Procyon lotor) (Wass and Wright 1969). 



Marshes with sufficient tidal flushing export 

 some of their annual carbon production to the Bay 

 (R. Wetzel, pers. comm. based on salt marsh model 

 research). Most export occurs in the winter, by ice 

 scouring and tidal flushing when standing dead 

 material is greatest (Heinle et al. 1976). Poorly 

 flooded marshes may not exchange any carbon 

 with the estuary on the Patuxent River, although 

 dissolved nitrogen and phosphorus are exported to 

 the estuary (Heinle and Flemer 1976). After Teal 

 (1962), it has been widely assumed that marshes 

 enhance the productivity of estuaries by exporting 

 much of the carbon produced. While it is probable 

 that there is a net export of carbon from marshes 

 along the Chesapeake, there is still disagreement 

 among scientists as to the role of marshes as con- 

 tributors to Bay production. 



Another unresolved aspect of the relationship 

 between the estuary and adjacent marshes is nu- 

 trient exchange. Marshes trap nutrients (both 

 natural and pollutants) from tributaries and upland 

 drainage (Silberhorn et al. 1974). Nutrients can be 

 temporarily stored in the marshes, and released 

 gradually to the Bay. The buffering capacity of 

 marshes is, however, limited and can be lost if large 

 nutrient inputs from sewage effluent saturate the 

 marsh (R. Wetzel, pers. comm.). 



Organic and inorganic nutrients also enter 

 marshes from the Bay. Nutrient exchange between 

 marshes and Bay waters involves changes in the 

 chemical forms of N and P, superimposed on a 

 probable net export of N and P to the Bay 

 (Axelrad 1974). The role of marshes in nutrient ex- 

 change is debated among scientists and requires 

 further research. 



The primary producers in coastal wetlands are 

 marsh plants with attached periphyton and benthic 

 algae (fig. !?). Species vary with the type of marsh 

 or mudflat. Most marsh plants enter the marsh 



