Authors: Michael Schramm

We quantified daily, monthly, and annual nutrient loading from freshwater segments in the Lavaca Bay watershed using a statistical modeling approach relating time and discharge to nutrient concentrations. Total combined annual nitrate loads ranged from 12,574 kg in 2011 to 794,510 kg in 2007 with a mean annual load of 205,405 kg per year from 2005 through 2020. Total combined annual total phosphorus loads ranges from 7,839 kg in 2011 to 916,908 kg in 2004 with a mean annual load of 241,681 kg per year from 2000 through 2020. Model validation indicated the approach performed well for predicting nutrient loads at the two most downstream sites in the watershed (Lavaca River near Edna, USGS-08164000 and Lake Texana at Palmetto Bend Dam, USGS-0816425). Additional flow-biased monitoring would improve model performance and validation during important high flow events that are the primary drivers of loading to Lavaca Bay. Model performance suffered at upstream sites to due higher variance in the measured data and insufficient sampling.

Authors: Duncan Kikoyo, Taylor Jordan, Shubham Jain, Michael Schramm, and Lucas Gregory

TCEQ first identified bacteria impairments within Thompsons Creek in the 2002 Texas Integrated Report of Surface Water Quality for the Clean Water Act Sections 305(b) and 303(d) and within Cottonwood Branch and Still Creek in the 2006 Texas Integrated Report. Bacteria impairments have been identified in each subsequent edition through 2020, e.g., the EPA-approved 2020 Texas Integrated Report. This document will consider five bacteria impairments in five assessment units (AUs) of the Cottonwood Branch, Still Creek, and Thompsons Creek. The impaired AUs and their identifying numbers are Cottonwood Branch (1242B_01, 1242B_02), Still Creek (1242C_01), and Thompsons Creek (1242D_01, 1242D_02).

Authors: Michael Schramm

Links between freshwater inflows, watershed nutrient loads and water quality in Lavaca Bay were explored using generalized additive models. This approach allowed the exploration of nonlinear relationships between upstream inputs and water quality responses while accounting for changes in water quality due to natural variations in precipitation and streamflow. Results show increasing concentrations of inorganic and organic nitrogen at select sites in Lavaca Bay, but no evidence of significant changes in chlorophyll-a or dissolved oxygen concentrations in recent years. Changes in freshwater inflow and, to a smaller extent, changes in watershed nutrient loading explain the variability observed in total phosphorus and nitrite+nitrate concentrations. Limited data and complex responses of chlorophyll-a, Total Kjeldahl Nitrogen, and dissolved oxygen to freshwater inflow and nutrient loadings point to a need for continued data collection and model development. Overall, the study provides a baseline assessment of how management activities in the watershed that are aimed at reducing nonpoint source pollution are linked with water quality in Lavaca Bay to date.

Authors: Emily Monroe, Lucas Gregory, Matthew McBroom, Jeremiah Poling and Rene Barelas

A watershed is defined as a land area where all water that flows across or through it is channeled to the same point, such as a stream, river, lake, or ocean. All lands are part of a watershed, from the smallest of backyards to the largest continent. The quality and quantity of water that flows into a water body impacts whether a habitat can support the chemical, physical, and biological communities within it. Watershed-based planning is a way to protect and restore water quality at local, manageable scales. The La Nana Bayou Watershed Protection Plan (WPP) is a comprehensive, stakeholder-driven approach to improving the water quality in the La Nana Bayou watershed of Nacogdoches, Texas.

Authors: Michael Schramm

Links between freshwater inflows, watershed nutrient loads and water quality in Lavaca Bay were explored using generalized additive models. This approach allowed the exploration of nonlinear relationships between upstream inputs and water quality responses while accounting for changes in water quality due to natural variations in precipitation and streamflow. Results show increasing concentrations of inorganic and organic nitrogen at select sites in Lavaca Bay, but no evidence of significant changes in chlorophyll-a or dissolved oxygen concentrations in recent years. Changes in freshwater inflow and, to a smaller extent, changes in watershed nutrient loading explain the variability observed in total phosphorus and nitrite+nitrate concentrations. Limited data and complex responses of chlorophyll-a, Total Kjeldahl Nitrogen, and dissolved oxygen to freshwater inflow and nutrient loadings point to a need for continued data collection and model development. Overall, the study provides a baseline assessment of how management activities in the watershed that are aimed at reducing nonpoint source pollution are linked with water quality in Lavaca Bay to date.

Authors: Taylor Jordan, Michael Schramm, Duncan Kikoyo and Amanda Tague

Among non-legacy contaminants, depressed dissolved oxygen (DO) is the second most frequent cause of water quality impairments in Texas. While much of the current focus of water quality efforts has been to address fecal indicator bacteria, substantial opportunity exists for addressing DO impairments. This report provides a review of methods and approaches used for developing DO Total Maximum Daily Loads (TMDLs) in the US Environmental Protection Agency (EPA) Regions 4 and 6. While many different approaches and models are available, TMDL development appears to have coalesced around only a few mechanistic models. In general, the use of linked watershed and receiving water body models is most common, with the choice of receiving water body model varying among the QUAL2E, WASP, and EFDC models. The development of frameworks for choosing modeling approaches using expertise available among agencies, universities and other stakeholders will help build consensus in decision-making prior to TMDL development. Due to the data requirements and model complexity in some of the identified approaches, additional discussion is needed to identify preliminary data needs for DO TMDL development. With anticipation of future DO TMDL (and other water quality planning efforts) development, this study suggests following a model similar to the previously convened Bacteria TMDL Task Force for providing expert guidance and building high-level consensus of approaches and data requirements for developing DO TMDLs within Texas.

Authors: Stephanie deVilleneuve and Amanda Tague

Throughout this project, routine water quality monitoring was conducted with a focus on collecting paired flow rate and E. coli concentration data in each selected tributary of the Little Brazos River. Data was collected at five sites (one per tributary) monthly for 21 months, resulting in 105 total samples (Figure 1). All sampling procedures, methods, sampling sites, and planned project activities are fully described in the project quality assurance project plan (QAPP). Monthly sampling included field parameters, streamflow measurement, and E. coli grab samples to sufficiently fill data gaps, thus enabling future water quality assessments and watershed analysis.

Water quality and quantity data were uploaded to the TCEQ Surface Water Quality Monitoring Information System (SWQMIS) for future waterbody assessments. Collected data and water quality findings and trends are summarized in this final project report to provide an informational basis for any future work conducted in these watersheds.

Authors: Lucas Gregory and Andy James

A watershed protection plan (WPP) for the Leon River below Proctor Lake and above Belton Lake was developed with funding from the Texas State Soil and Water Conservation Board (TSSWCB) and the United States Environmental Protection Agency (EPA). The WPP received final acceptance from the EPA in 2015. A full-time watershed coordinator position was considered critical in initiating and carrying out the implementation process by the watershed steering committee. This watershed coordinator position was filled by a local individual in a full-time capacity until late 2021. That person moved on and the Texas Water Resources Institute (TWRI) took over the role in a limited capacity. The watershed coordinator provided technical assistance to stakeholders, coordinated outreach and education efforts, assisted in securing funding for bacteria source tracking (BST), and tracked water quality to identify implementation impacts. Education and outreach efforts have included workshops, field days, and presentations by the watershed coordinator and other relevant experts. Implementation efforts have proven successful with several assessment units being delisted from the state’s list of impaired waterbodies, while several others have been proposed to be delisted by the Texas Commission on Environmental Quality (TCEQ). However, eight of the twelve assessment units in the watershed remain impaired due to elevated bacteria concentrations. Additionally, bacteria concentrations are generally trending higher across the watershed despite implementation efforts to date.