Nitrogen and phosphorus budgets in estuaries of the Texas Coast

A Thesis Submitted In Partial Fulfillment of the Requirements for the Degree of MASTER OF SCIENCE in Environmental Science from Texas A&M University-Corpus Christi.Estuaries are highly valuable ecosystems that depend on nutrients for their productivity. On-going urbanization and socio-economic activities are constantly affecting nutrient dynamics and estuarine organisms. The purpose of this study was to determine how hydrology affects nutrient budgets in Texas estuaries through biogeochemical budget modeling under the land-ocean interaction in the coastal zone (LOICZ) guidelines. LOICZ budgets were applied to the seven major estuaries in Texas to address the long-term water, salt, and nutrient budgets to calculate daily averages using various datasets from multiple agencies. The Laguna Madre Estuary was further separated into two budgets: the Lower Laguna Madre Estuary and the Upper Laguna Madre Estuary. The results revealed that the climate gradient plays a crucial role in the water budgets indicating that precipitation is a main driving factor to inflow balance. In addition, inflow balance is a main driving factor to salinity and nutrient concentrations among these estuaries. However, external factors such as urbanization, return flows, and agricultural runoff have elevated the nutrient levels in two estuaries. The Trinity-San Jacinto Estuary had higher daily average dissolved inorganic phosphorus (DIP) and total phosphorus (TP) levels compared to the other estuaries due to the large population density of Houston, TX, and the frequent use of detergents and possible fecal and urine waste in wastewater return flows. In contrast, the Upper Laguna Madre Estuary higher total Kjeldahl nitrogen (TKN) compared to the other estuaries due to its unique geographical features and inflow primarily dominated by sewage and agricultural runoff. The implications of these results are that altered hydrology can alter the nutrient dynamics of these estuaries and can affect biological productivity and water quality in an estuary.Environmental ScienceCollege of Scienc