TIDE GATE INFLUENCES ON A TIDAL MARSH

Construction of a tide gate at the mouth of the north channel of the S avannah River in Georgia has resulted in significant changes in salini ties influencing marsh community changes. The tide gate is directly re sponsible for a 2 to 6 mile upstream displacement of salt water in the river. In the marsh, soil salinities ranged from 0.0 ppt at upstream sites to 12 ppt at downstream sites when the tide gate was in operatio n. Within two months of taking the tide gate out of operation, interst itial salinities at the downstream sites dropped to 4 ppt. Influences of the tide gate on marsh vegetation were modeled in a geographic info rmation system. With the tide gate out of operation, the model predict s that freshwater marsh would increase in area by 340 percent.