Guidelines for Water Resources Permitting: Nutrient Requirements for Maintenance of Galveston Bay Productivity

The work described here was supported by the Texas Water Development Board (TWDB) and in by the USEPA. The guiding purpose was to provide new data and a new synthesis of this new and existing data to aid management of Galveston Bay, Trinity-San Jacinto Estuary, resources. The approaches presented here are also applicable to other Texas bays. Section I presents nitrogen and phosphorus budgets for Galveston Bay during low inflow and high inflow periods. The section ends with proposals of specific minimum nitrogen and phosphorus requirements to maintain characteristic productivity of Galveston Bay. These are evaluated through budget analysis and reference to historic conditions. Section II is an analysis of community production and respiration in Galveston Bay from application of the diurnal curve technique to TWDB Datasonde dissolved oxygen data. Derivation of nutrient requirements from the results in explored, through comparison of demands from primary producers with supply from regeneration and from outside sources. Section III presents a STELLA model based on quantification of relationships between freshwater inflow and components of the Galveston Bay nitrogen budget. The model is used to test the sensitivity of the system nitrogen dynamics to assumptions and uncertainty in the data. The model also shows system-level outcomes of components variously responding to changes, such as reductions in freshwater inflows. Every effort was made to conduct analyses in an objective fashion and to clearly indicate where situations required professional judgment to substitute for missing information. Where analyses described below involve assumptions and professional judgment, these reflect the opinions of the authors, and may not reflect the official positions of the supporting agencies.