Examination of the Spatial Relationship between Development Metrics and Total Phosphorus in the Galveston Bay Estuary

Urban development can cause increased nutrient loads in nearby streams and rivers. Understanding how the pattern of urban development affects the level of nutrients, specifically phosphorus, within the Galveston Bay Estuary is particularly important for planners and policymakers working to maximize the water quality within the region. The problem of eutrophication that results from increased nutrients can be detrimental to the health of the ecosystem; further, the rapid population growth within the Galveston Bay Estuary is increasing development within the area. The ecosystem-based study described here examines 99 watersheds across the Galveston Bay Estuary, Texas. Multiple development metrics are evaluated for both high and low intensity development and these development patterns are related to total phosphorus as an indicator of water quality. Spatial lag models were used to determine the relationship between the high intensity and low intensity development and phosphorus levels. It was hypothesized and validated by the results that less fragmented and more connected urban development patches within the Galveston Bay Estuary relate to lower phosphorus levels. In addition, as the proportion of low intensity development increases within a watershed, phosphorus levels are also increased due to runoff from fertilizer. Phosphorus-based fertilizer runoff has increased in the region and is likely driven by the use of fertilizers on urban and rural homes. The results from this study can be implemented in planning and policy through a series of tools including development clustering, urban growth boundaries, transfer of development rights, education and outreach, and implementation of laws. Each planning tool offers a way to aggregate the low intensity development in a manner that will reduce the phosphorus levels within the study area; this, in turn, will decrease the probability of eutrophication that can result in streams with nutrient loading problems. In addition, there are a large amount of phosphorus-based fertilizers used in the region, and reducing these levels will aid in decreasing the phosphorus levels within the rivers and streams