The marine biota from the middle Pennsylvanian outcrops of the Sierra Agua Verde, located in mid-eastern Sonora, consists of phylloid algae of the genera Komia and Eugonophyllum and a number of invertebrates. These species include bioaccumulations of chaetetids; brachiopods of the genera Dielasma sp., Reticulariina sp., Anthracospirifer sp., Antiquatonia sp.; bryozoans of the genus Thamniscus; tabulate corals such as Syringopora and solitary corals such as Zaphrentis; fusulinid foraminifera such as Pseudostaffella, Eoshubertella texana, Fusulinella llanoensis, and Zellerella; gastropods of the genus Euomphalus and Donaldina; and the crinoid genera Cyclocaudex, Cyclocrista, Heterosteleschus, Lamprosterigma, Mooreanteris, Pentagonopternix, Preptopremium, Cycloscaspus, and Pentaridica. The material was collected from outcrops in the first 512m of the La Joya Formation, and their sediments have a total thickness of 780m and consist of limestone interbedded with calcareous mudstone and sandstone lenses. The age of the middle Pennsylvanian strata corresponds to that of the Atokan stage (311 million years). The species assemblages are typical of a shallow tropical marine benthos. The analysis of the distribution of the species allowed for the determination of their paleogeographic relationships with the components of the biota of the Carboniferous strata of Texas and Kansas in the United States of America, which belong to the province of the North American Craton.

A combined simulation-optimization model was developed to minimize the freshwater footprint at multi-well hydraulic fracturing sites. The model seeks to reduce freshwater use by blending it with brackish groundwater and recovered water. Time-varying water quality and quantity mass balance expressions and drawdown calculations using the Theis solution along with the superposition principle were embedded into the optimization model and solved using genetic algorithms. The model was parameterized for representative conditions in the Permian Basin oil and gas play region with the Dockum Formation serving as the brackish water source (Texas, USA). The results indicate that freshwater use can be reduced by 25–30 % by blending. Recovered water accounted for 2–3 % of the total blend or 10–15 % of total water recovered on-site. The concentration requirements of sulfate and magnesium limited blending. The evaporation in the frac pit constrained the amount blended during summer, while well yield of the brackish (Dockum) aquifer constrained the blending during winter. The Edwards-Trinity aquifer provided the best quality water compared to the Ogallala and Pecos Valley aquifers. However, the aquifer has low diffusivity causing the drawdown impacts to be felt over large areas. Speciation calculations carried out using PHREEQC indicated that precipitation of barium and strontium minerals is unlikely in the blended water. Conversely, the potential for precipitation of iron minerals is high. The developed simulation-optimization modeling framework is flexible and easily adapted for water management at other fracturing sites.

Goodenough Spring (Texas, USA) is a large spring near the border of the American state of Texas and the Mexican state of Coahuila, discharging into the international Amistad Reservoir on the river Rio Grande (Rio Bravo). Discharge was routinely measured from 1928 until 1968 to partition the flow of the river between the two countries in accordance with water-use treaties. Samples were analyzed for water-quality parameters in 1967–1968 prior to inundation under 45 m of Amistad Reservoir in 1968. Subsequently, discharge has been estimated indirectly by the International Boundary and Water Commission (IBWC). For the first direct measurements of the spring in 37 years, velocity and cross-sectional measurements were made and water samples collected in the summer of 2005 using advanced self-contained underwater breathing apparatus (SCUBA) techniques. Spring discharge was calculated at 2.03 m³ s–¹, approximately one-half of the historical mean of 3.94 m³ s–¹. In situ and laboratory analyses of samples for temperature, pH, dissolved oxygen, specific conductance, alkalinity, nitrate-nitrogen, dissolved solids, chloride, sulfate, fluoride, phosphorus, calcium, sodium, potassium, magnesium, and iron showed the water quality to be very good for human consumption and crop irrigation. Measurement values are relatively unchanged from those reported 37 years prior.

Understanding groundwater salinity sources in the Gulf Coast Aquifer System (GCAS) is a critical issue due to depletion of fresh groundwater and concerns for potential seawater intrusion. The study objective was to assess sources of groundwater salinity in the GCAS using ∼1,400 chemical analyses and ∼90 isotopic analyses along nine well transects in the Texas Gulf Coast, USA. Salinity increases from northeast (median total dissolved solids (TDS) 340 mg/L) to southwest (median TDS 1,160 mg/L), which inversely correlates with the precipitation distribution pattern (1,370– 600 mm/yr, respectively). Molar Cl/Br ratios (median 540–600), depleted δ²H and δ¹⁸O (−24.7‰, −4.5‰) relative to seawater (Cl/Br ∼655 and δ²H, δ¹⁸O 0‰, 0‰, respectively), and elevated ³⁶Cl/Cl ratios (∼100), suggest precipitation enriched with marine aerosols as the dominant salinity source. Mass balance estimates suggest that marine aerosols could adequately explain salt loading over the large expanse of the GCAS. Evapotranspiration enrichment to the southwest is supported by elevated chloride concentrations in soil profiles and higher δ¹⁸O. Secondary salinity sources include dissolution of salt domes or upwelling brines from geopressured zones along growth faults, mainly near the coast in the northeast. The regional extent and large quantities of brackish water have the potential to support moderate-sized desalination plants in this location. These results have important implications for groundwater management, suggesting a current lack of regional seawater intrusion and a suitable source of relatively low TDS water for desalination.

Understanding groundwater-pumpage sources is essential for assessing impacts on water resources and sustainability. The objective of this study was to quantify pumping impacts and sources in dipping, unconfined/confined aquifers in the Gulf Coast (USA) using the Texas Carrizo-Wilcox aquifer. Potentiometric-surface and streamflow data and groundwater modeling were used to evaluate sources and impacts of pumpage. Estimated groundwater storage is much greater in the confined aquifer (2,200 km3) than in the unconfined aquifer (170 km3); however, feasibility of abstraction depends on pumpage impacts on the flow system. Simulated pre-development recharge (0.96 km3/yr) discharged through evapotranspiration (ET, ∼37%), baseflow to streams (∼57%), and to the confined aquifer (∼6%). Transient simulations (1980–1999) show that pumpage changed three out of ten streams from gaining to losing in the semiarid south and reversed regional vertical flow gradients in ∼40% of the entire aquifer area. Simulations of predictive pumpage to 2050 indicate continued storage depletion (41% from storage, 32% from local discharge, and 25% from regional discharge capture). It takes ∼100 yrs to recover 40% of storage after pumpage ceases in the south. This study underscores the importance of considering capture mechanism and long-term system response in developing water-management strategies.

Water resources in agriculture-dominated basins of the arid western United States are stressed due to long-term impacts from pumping. A review of 88 regional groundwater-flow modeling applications from seven intensively irrigated western states (Arizona, California, Colorado, Idaho, Kansas, Nebraska and Texas) was conducted to provide hydrogeologists, modelers, water managers, and decision makers insight about past modeling studies that will aid future model development. Groundwater models were classified into three types: resource evaluation models (39%), which quantify water budgets and act as preliminary models intended to be updated later, or constitute re-calibrations of older models; management/planning models (55%), used to explore and identify management plans based on the response of the groundwater system to water-development or climate scenarios, sometimes under water-use constraints; and water rights models (7%), used to make water administration decisions based on model output and to quantify water shortages incurred by water users or climate changes. Results for 27 model characteristics are summarized by state and model type, and important comparisons and contrasts are highlighted. Consideration of modeling uncertainty and the management focus toward sustainability, adaptive management and resilience are discussed, and future modeling recommendations, in light of the reviewed models and other published works, are presented.

The determination of space–time variation in groundwater accumulation in Colombia’s Eastern Llanos foreland basin from 2003 to 2014 was done using terrestrial water storage (TWS) anomalies identified in two versions of the Gravity Recovery and Climate Experiment (GRACE) data—from the Global Data Center for Space Research (CSR) at the University of Texas at Austin (USA) and from the Institute of Geodesy at the Graz University of Technology (ITSG, Austria)—and also soil moisture storage (SMS) data from the Global Land Data Assimilation System (GLDAS). These data were compared to changes in groundwater storage obtained using the water-budget equation, calculated based on recorded data from hydrometeorological stations. This study confirmed the viability of using satellite information to understand and monitor temporal variation in groundwater recharge in the study area. Temporal variations in TWS, SMS, and groundwater level were shown to correspond to regional rain and drought periods, which are sensitive to climate phenomena such as El Niño and La Niña. Comparing changes in TWS and groundwater level to changes in infiltration and recharge revealed correlation coefficients of 0.56 and 0.98 with CSR data and 0.71 and 0.86 with ITSG data, respectively.

Periodic releases from an upstream dam cause rapid stage fluctuations in the Lower Colorado River near Austin, Texas, USA. These daily pulses modulate fluid exchange and residence times in the hyporheic zone where biogeochemical reactions are typically pronounced. The effects of a small flood pulse under low-flow conditions on surface-water/groundwater exchange and biogeochemical processes were studied by monitoring and sampling from two dense transects of wells perpendicular to the river. The first transect recorded water levels and the second transect was used for water sample collection at three depths. Samples were collected from 12 wells every 2 h over a 24-h period which had a 16-cm flood pulse. Analyses included nutrients, carbon, major ions, and stable isotopes of water. The relatively small flood pulse did not cause significant mixing in the parafluvial zone. Under these conditions, the river and groundwater were decoupled, showed potentially minimal mixing at the interface, and did not exhibit any discernible denitrification of river-borne nitrate. The chemical patterns observed in the parafluvial zone can be explained by evaporation of groundwater with little mixing with river water. Thus, large pulses may be necessary in order for substantial hyporheic mixing and exchange to occur. The large regulated river under a low-flow and small flood pulse regime functioned mainly as a gaining river with little hydrologic connectivity beyond a narrow hyporheic zone.

This study presents a three-dimensional reactive transport model to simulate upward and lateral migration of CO₂ plumes under different scenarios through a leaky section of a plugged and abandoned well at a hypothetical CO₂ storage site into the Texas Gulf Coast Aquifer (TGCA). The TGCA is the most active region in research and operation of carbon capture, utilization, and storage, with the largest technically accessible resource of CO₂ storage, in the United States. The results suggest that dissolved inorganic carbon (DIC) concentration and pH, better than Cl concentration (or total dissolved solids), can be indicators for leakage detection in the TGCA; DIC has earlier detection time than pH. The modeling results show that detection of CO₂ leakage in the shallow aquifers may take hundreds of years because of the confining unit in the TGCA, suggesting that (1) monitoring wells should be placed as deep as possible and (2) characterization of confining units in the overlying aquifer system is critical. Regional hydraulic gradient and groundwater pumping in the TGCA are important factors for monitoring well placement. While this study was conducted in the TGCA, the results provide valuable information for groundwater monitoring at other geological carbon sequestration sites.