Decline of submerged vegetation in the Galveston Bay system: chronology and relationships to physical processes

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Pulich, Warren
White, William Allen, 1939-

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The Galveston Bay complex of Texas ranks as the 7th largest estuary in the USA, including 143,000 ha (about 554,000 acres) of open water and approximately 93,000 ha (230,000 acres) of wetlands (Diener 1975), of which about 48,000 ha (about 118,000 acres) are marshes and swamps (Fisher et al. 1972). These habitats support finfish and shellfish populations which annually account for 28 percent of the total Texas commercial bay fisheries landings, 67 percent of the Texas oyster harvest (Avg. 3.6 million pounds), and 30 percent of blue crab and shrimp harvests (NOAA 1989). This production is sustained by a combination of high freshwater inflows from the Trinity-San Jacinto Rivers, nutrient cycling dynamics of bay wetlands, and nursery grounds afforded by shallow-water habitats. Despite its inherent natural resource value, Galveston Bay has been heavily impacted by shoreline industrial and municipal development, excess inputs of pollutants and wastewater discharges, channelization, dredging projects, subsidence, and alterations in bay-water circulation dynamics. Degradation of the bay-system's water quality has increased to the point that over 38 billion gallons a day of waste effluents are discharged into the bay and its tributaries (NOAA 1989). A decline of approximately 90 percent in bay submerged vascular vegetation (SV) since 1956 (when aerial photographs indicate approximately 2,070 ha -- 5,120 acres: Fisher et al. 1972) is an alarming environmental impact (NOAA 1989) because of the loss in fisheries nursery habitat. The disappearance of this valuable subtidal habitat has received widespread attention with the recent designation of Galveston Bay as a national estuary by the EPA National Estuary Program (NOAA 1989). Review of the chronological sequence of SV habitat loss has been recommended to help determine critical factors threatening estuarine habitats and to design management solutions for restoration of impacted SV habitat. We have completed a study, which examines major regions of Galveston Bay where submerged halophytes have declined since the 1950's and compares them with nearby remaining sites where plants still persist. The approach involved compilation and analysis of active processes and hydrologic data, which could affect distribution and abundance of rooted estuarine plants. After the SV distribution at different time periods was mapped, physical and hydrologic factors were analyzed in an attempt to establish the processes contributing to impacts on SV habitats. This report is part of a study funded by the Texas Parks and Wildlife Department and Texas Water Development Board with funds allocated by the Texas Legislature for comprehensive studies of the effects of freshwater inflows on the bays and estuaries of Texas.


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