Land Use/Land Cover Change and its impacts on Streams and Estuarine Water Quality in the Galveston Bay Watershed, Texas

Abstract

The nature of society's relationship with coastal environments is illustrated well by Galveston Bay watershed in Texas, which is an important economic, recreational, and environmental asset. However, the watershed has been altered by growth in the port of Houston and by human populations and industry. High rates of inter-basin transfer of water was observed from the USGS stream gauging station data for those stations lying within the highly urbanized area with increasing trends in river discharge. Land use and land cover classification for the lower Galveston Bay watershed from 1989-2009 showed an increase in urban growth followed by a decrease in agriculture and forest cover. Land cover data for four selected catchments: Brays Bayou, Greens Bayou, East Fork San Jacinto and West Fork San Jacinto within the Galveston Bay watershed were combined for "space for time-substitution" analysis to increase the number of observations and check for correlations between percent land cover and stream hydrology and stream chemistry with significant results. Variations in percent urban, forest, pasture and wetlands explained most of the variability in water yield followed by rainfall which had a small but significant effect. Results of the analysis clearly demonstrated increasing water yields and nutrient inputs with increasing urban land use. Population changes explained the increasing trends in water yields for the highly urbanized catchments of Brays Bayou and Greens Bayou. Similarly, highly significant positive relationships were observed between river nutrients and total population for Brays Bayou, Greens Bayou, and the West Fork San Jacinto catchments. Results from this research show that anthropogenic changes in the watershed have a significant impact on the river flow and stream water quality. Continued development and future population growth in the highly urbanized areas near Houston will cause increasing water demand from adjacent watersheds resulting in higher downstream flows in the estuary. Increasing freshwater flow in the estuaries results in higher nutrient loading and Bay stratification. Higher rates of stratification caused by rising temperatures as a result of global warming and larger freshwater flow along with increased nutrient inputs will increase the vulnerability of the Galveston Bay to severe eutrophication during the warm summer months.