Hydrologic Trends in the Upper Nueces River Basin of Texas—Implications for Water Resource Management and Ecological Health

Reliable water sources are central to human and environmental health. In south Texas, USA, the Nueces River Basin (NRB) directly or indirectly plays that important role for many counties. Several NRB stream segments are designated as ecologically significant because they serve crucial hydrologic, ecologic, and biologic functions. The hydrologically significant streams recharge the Edwards Aquifer, an essential water source for the region’s agricultural, industrial, and residential activities. Unfortunately, the semiarid to arid south Texas climate leads to large inter-annual precipitation variability which impacts streamflow, and as a consequence, the aquifer’s recharge. In this study, we used a suite of hydrologic metrics to evaluate the NRB’s hydroclimatic trends and assess their potential impacts on the watershed’s ecologically significant stream segments using precipitation and streamflow data from the National Climatic Data Center (NCDC) and Hydroclimatic Data Network (HCDN) respectively from 1970 to 2014. The results consistently showed statistically significant decreasing streamflow for certain low-flow indicators over various temporal scales, likely due to water rights diversions and minimal land use changes. This research could help decision-makers develop the necessary tools to manage water resources in south Texas, given the NRB’s significance as a source of water for domestic consumption and ecological health.

Multispecies and Watershed Approaches to Freshwater Fish Conservation

<em>Abstract</em>.—From off-road vehicle abuse in streambeds to nonnative invasive species in riparian areas, from the threat of wastewater discharge in pristine headwater creeks to proposals for burying low-level radioactive waste and landfilling of fracking byproducts on floodplains, from water marketing plans seeking to export large quantities of groundwater to bulldozing river channels, gravel mining, and diverting stream flows, it’s not easy to save a river. It is really all about the people; <em>Homo sapiens </em>are an essential species of consideration in any multispecies approach to conservation. The Nueces River Authority (NRA) has served as a guardian of surface-water resources in the Nueces River basin since the agency was created by the Texas Legislature in 1935. The jurisdiction of NRA includes portions of three ecoregions and 22 South Texas counties and encompasses more than 45,300 km2, extending from Rocksprings to the Gulf of Mexico. Over the past eight decades, NRA has strived to develop and implement an adaptive, systems approach that focuses on empowering people with good information and consistent messaging in order to restore and protect the Nueces River.

Implementation of a Hydrodynamic Model for Salinity in Nueces and Corpus Christi Bays

The purpose of this research was to implement and calibrate a hydrodynamic model for Nueces Bay, Texas and use said model to predict how salinity and circulation in the bay could be affected by sea level rise and changes in freshwater input. The Nueces Bay estuary is fed fresh water from the Nueces River and connects to Corpus Christi Bay, which connects to the Gulf of Mexico. Salinities in Nueces Bay range from near 0 PSU at times of high riverine flow to over 50 PSU during drought periods. The model selected is the Finite Volume Coastal Ocean Model (FVCOM), an unstructured grid, finite-volume, three-dimensional primitive equation ocean model developed for the study of coastal oceanic and estuarine circulation.An unstructured triangular mesh was created for the bay and bathymetry was interpolated to the mesh. Forcing inputs included water level, water temperature, salinity, wind speed and direction, and the flow rate of the Nueces River. Several software utilities were created to facilitate set-up and testing of the model. Predictions were compared with measured water levels and salinity at several locations in the study area for years 2008 &amp; 2010.The model produced good results for water level predictions with a mean absolute error of 6.5 cm over the test period. The model also produced overall realistic currents and salinity variations in Corpus Christi Bay with a mean absolute error of 1.7 psu at Ingleside. However, the model predicted salinity poorly in Nueces Bay with a mean absolute error greater than 6 psu at all stations and a maximum absolute error of greater than 20 psu. While its initial goal was to investigate the impact of sea level rise on salinity levels, the study focused instead on model performance for salinity predictions in Nueces Bay. The investigation revealed that while freshwater from the Nueces River was entering the system at the correct rate, the model was not accurately reflecting salinity response in cells further down river and ultimately in Nueces Bay.

Inorganic nitrogen release from sediment slurry of riverine and estuarine ecosystems located at different river regimes

The purpose of the present study was to compare the nature of dissolved inorganic nitrogen (DIN=ammonium (NH4+) and nitrite+nitrate (NO2+3=(NO2–+NO3–)) release from aerobic sediment slurry at two different hydrologic flow regimes. The watershed of the Guadalupe River–Estuary system receives more freshwater inflow than does the watershed of the Nueces River–Estuary system; thus, the Nueces Estuary is more saline than is the Guadalupe Estuary. Sediment samples were collected using cores, analysed for organic matter and grain size, and used to perform laboratory experiments to measure DIN release. During the experiments, DIN concentrations in overlying water were measured for 48h in five different salinity treatments. Ammonium concentrations were higher in the Nueces River and Estuary treatments than in similarly treated samples from the Guadalupe River and Estuary. An increase in NO2+3 concentrations along salinity gradients of the Nueces Estuary treatments indicated favourable condition for nitrification. The Guadalupe River sediments that were not exposed to salinity had an increase in NH4+ concentration at 7.5ppt. The different DIN release among salinity treatments indicated that hydrologic forcing on organic matter deposition and salinity have an important role on the retention and release of inorganic nitrogen at the sediment–water aerobic layers in rivers and estuaries.