How does salinity affect the Chesapeake Bay?
Salinity, the concentration of salts in the water, is extremely important to aquatic life. In the Chesapeake Bay and its tributaries, salinities range from less than 0.5 parts per thousand (ppt) in non-tidal and tidal fresh areas to about 30 ppt at the mouth of the Bay. Ocean water is generally around 36 ppt. Salinities are higher on the eastern side of the Bay than on the western side due in part to the Coriolis effect of the earth’s rotation and in part because more freshwater is discharged from rivers along the western shore of the Bay.
Salinities are highest after dry weather periods and lowest after wet weather or snowmelt periods. This is why salinities are usually lowest in April and May, after the spring rains, and increase in August and September after the summer, which is usually a drier period. In rainy years salinities are lower than usual and in drought years they are higher.
Many plant and animal species can live only in a restricted salinity range. For example, the bay grass wild celery lives in fresh to brackish reaches of the Bay and its tributaries, while eelgrass lives only in higher salinity areas of the Bay. Thus changes in salinity determine what plant and animal species live in a given area. Abrupt changes in salinity can be particularly harmful to many species.
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