An Integrated Assessment of Nutrient Loading to Baffin Bay, Texas
Baffin Bay — the “jewel” of the Texas coast — provides critical habitat for important fish species. However, it currently exhibits symptoms of water quality degradation that threaten the health of the bay and its valuable fishery. Persistent brown tide algal blooms are particularly troublesome due to negative impacts on seagrass beds and disruption of the food web.
In 2013, a volunteer water quality monitoring program was initiated to better understand the extent and causes of water quality degradation in the system. The study revealed that dissolved organic nitrogen (DON), linked to brown tide algal blooms in other systems, was two- to three-fold higher in Baffin Bay than other Texas estuaries. Analysis of historical Texas Commission on Environmental Quality (TCEQ) data showed that Baffin Bay has undergone a long-term increase (since the 1970’s) in chlorophyll A (a proxy for algal biomass) along with long-term seasonal increases in water temperature and total Kjeldahl nitrogen (mostly as organic nitrogen). In addition, the TCEQ data shows very high chlorophyll and nutrients in creeks that drain into Baffin Bay.
To improve Baffin Bay ecosystem health, a large-scale watershed restoration aimed at reducing nutrient loads is needed. To do this, a reasonable accounting of nutrient sources must be in place. A 2012 modeling study determined that, of the land-derived nutrients, fertilizer accounted for ~30% of nitrogen loadings, followed by manure (20%), urban runoff and wastewater (10% each). The relative importance of these sources may vary spatially however, as one of the creeks draining into Baffin Bay (Petronila Creek) is surrounded mostly by agricultural and ranch lands, while another (San Fernando Creek) is influenced by multiple municipal wastewater sources. Furthermore, field sampling in 2017-2018 estimated that sewage (e.g. septic systems, wastewater outfalls) contributes 53±4% of the DON in the bay. The earlier modeling study also did not account for benthic influences, whereas recent sampling estimated that submarine groundwater discharge may contribute higher nutrient loads than surface runoff.
An interdisciplinary team of researchers at the Harte Research Institute for Gulf of Mexico Studies (HRI) intend to quantify nutrient loadings to Baffin Bay from surficial, groundwater/benthic and atmospheric sources. The goal of the project is to identify the main source(s) of nutrients to help prioritize watershed restoration activities. To do this, the team will first conduct coordinated, spatially-explicit sampling in the bay and watershed over an 18-month period, combining standard water quality measurements with isotopic tracers and flux measurements to establish load estimates from various sources. This data will then feed into a SWAT model, which will be used to simulate loadings under various hydrologic conditions and quantify hot spots. Model output will ultimately be used to support prioritization of both the type(s) of watershed restoration activities needed and regions of the watershed that require the most attention. To this end, the research team will work closely with relevant agency-based coastal resource managers to ensure that project results are integrated into their decision-making process.