Inflow needs assessment : effect of the Colorado River diversion on benthic communities




Montagna, Paul A.

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The Lavaca-Colorado Estuary has three major sources of freshwater inflow: the Lavaca, Tres Palacios, and Colorado Rivers. In 1991 the Colorado River was diverted to increase freshwater inflow into the east arm of Matagorda Bay. it was hypothesized that increased freshwater inflow would enhance productivity in the bay. The goal of this study was to determine the status of the bay and effectiveness of the water management program. Six stations were chosen along the major inflow gradients of the Lavaca and Colorado Rivers, and sampled quarterly for one year. Benthic macrofaunal abundance, biomass and community structure was measured. Observed salinity gradients at the stations indicated that marine water was diluted by freshwater near the mouthes of the rivers. Lavaca Bay and the east arm of Matagorda Bay had similar, low salinity characteristics. Both areas had similar community structure, and were typical of low salinity zones of Texas estuaries. However, there was an obvious enhancement of abundance, biomass and diversity in the east arm of Matagorda Bay (near the diversion of the Colorado River) relative to Lavaca Bay. These results indicate that the diversion probably has enhanced the productivity and health of Matagorda Bay. The only confounding factor is that the east end of Matagorda Bay also has less development than Lavaca Bay.



February 1994
To Lower Colorado River Authority ... Austin, Texas