Abstract:

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 and return flows have elevated the nutrient levels in two estuaries. The Trinity-San Jacinto Estuary had higher daily average dissolved inorganic phosphorus (DIP) and total phosphorus (DIP) levels compared to the other estuaries due to the large population density of Houston, TX, and the frequent use of detergents in wastewater return flows. In contrast, the Upper Laguna Madre Estuary higher total Kjeldahl nitrogen (TKN) compared to the other estuaries due to the lack of freshwater inflow and constant recycling of “old” nitrogen. 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.

Suggested Citation:

Marshall, Danielle A. and Paul A. Montagna. 2023. Nitrogen and phosphorous land-ocean interaction in the coastal zone (LOICZ) budgets for Texas estuaries. Distributed by: GRIIDC, Harte Research Institute, Texas A&M University–Corpus Christi. doi:10.7266/7gx3tv5c

Purpose:

To determine the effect of hydrology on the nitrogen and phosphorus nutrient budgets in Texas estuaries.

Data Parameters and Units:

Alkalinity, total (mg/L as CaCo3); Carbon, total organ , NPOC (TOC), mg/L; Chloride (mg/L as CL) flow stream, instantaneous (cubic feet per second); Nitrate nitrogen, total (mG/L as N); Nitrate nitrogen, bottom deposit (mg/kg-N); Nitrate nitrogen, total (mg/L as N); Nitrite plus nitrate, dissolved (mg/L as N); Nitrite plus nitrate, total (mg/l as N); Nitrogen Kjeldahl total bottom deposit (dry weight mg/kg as N); Nitrogen, ammonia, total (mg/l as N); Nitrogen, Kjeldahl, dissolved (mg/l as N); Nitrogen, Kjeldahl, total (mg/l as N); Nitrogen, organic, total (mg/l as N); Nitrogen, total (mg/l as N); Orthophosphate phosphorus, dissolved (mg/l as PO4); Oxygen, dissolved (mg/l); pH (standard units); Phosphate, ortho (mg/l as PO4); Phosphate, total (mg/l as PO4); Phosphorus, dissolved (mg/l as P); Phosphorous, total, wet method (mg/l as P); Phosphorus, total, bottom deposit (mg/kg dry weight); Salinity (parts per thousand); Specific conductance, field (us/cm at 25C); Specific conductance, lab (umhos/cm at 25C); Sulfate (mg/l as SO4); Temperature, water (degrees centigrade); Gross precipitation (inches/month); Precipitation Area (ac-ft/month); Gaged flow (ac-ft/month); Modeled flow (ac-ft/month); Diversion flow (ac-ft/month); Return flow (ac-ft/month).

Methods:

A daily time series of historical freshwater inflow into all Texas bays has been assembled for the period from January 1, 1940, through December 31, 2020. The primary source for this data is the input file for the TWDB TxBLEND salinity circulation model. The data used to develop these historical inflow sets are available on TWDB’s Water Data for Texas webpage (https://waterdatafortexas.org/coastal/hydrology/) and includes gage flows, measured at USGS streamflow gage locations, ungaged flows, estimated from a rainfall runoff model (TxRR) and diversion and return flows downstream of USGS gauge locations. The precipitation data have been recorded from 1940 through 2020 while the evaporation data have been recorded from 1954 through 2020 and were obtained from the Global Historical Climatology Network (GHCN) database found on the NOAA National Centers for Environmental Information (NCEI) website (https://www.ncei.noaa.gov/cdo-web/). Nutrient data was obtained from the Texas Commission of Environmental Quality (TCEQ) Surface Water Quality Web Reporting Tool (https://www80.tceq.texas.gov/SwqmisPublic/index.htm).

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