A Granger Causality Analysis of Groundwater Patterns over a Half-Century

Groundwater depletion in many areas of the world has been broadly attributed to irrigation. However, more formal, data-driven, causal mechanisms of long-term groundwater patterns have not been assessed. Here, we conducted the first Granger causality analysis to identify the causes of groundwater patterns using the rice-producing parishes of Louisiana, USA, as an example. Trend analysis showed a decline of up to 6 m in groundwater level over 51 years. We found that no single cause explained groundwater patterns for all parishes. Causal linkages were noted between groundwater and area harvested, number of irrigation wells, summer precipitation totals, and drought. Bi-directional linkages were noted between groundwater and rice yield, suggesting feedback between both time series. Causal linkages were absent between groundwater and many drivers where significant correlations were noted, highlighting the importance of using robust causal relationships over illusive correlations to detect the cause. These results advance our understanding of groundwater dynamics and can reveal a key connection between food and groundwater

Small-Scale Catchment Analysis of Water Stress in Wet Regions of the U.S.: An Example from Louisiana

Groundwater is increasingly being overdrafted in the Southeastern U.S., despite abundant rainfall and the apparent availability of surface water. Using the state of Louisiana as an example, the current study quantifies the stresses on water resources and investigates the potential for opportunities to use surface water in lieu of groundwater pumping. The assessment is based on a fine watershed scale (12-digit Hydrological Unit Code [HUC] boundaries) water balance between the availability of surface and groundwater and surface water and groundwater demand. Water demand includes environmental flows, as well as public supply, rural domestic, industrial, power generation, agricultural, and aquaculture sectors. The seasonality of water stress is also addressed by incorporating monthly variations in surface water supply and irrigation demands. We develop several new weighting schemes to disaggregate the water withdrawals, provided by the U.S. Geological Survey on a county scale, to the HUC12 scale. The analysis on the smaller HUC12 scale is important for identifying areas with high water stress that would otherwise be masked at a larger scale (e.g. the county or HUC8 watershed scales). The results indicate that the annual water stress in Louisiana is below one (i.e. there is more water available than is used) for most watersheds; however, some watersheds (15 of the HUC12 units) show stresses greater than one, indicating an insufficient water supply to meet existing demands. The areas of the highest water stress are largely attributable to water consumption for power generating plants or irrigation. Moreover, estimating the stresses on surface water and groundwater sources separately confirms our speculation of abundant surface water and demonstrates a significant over-drafting/deficit of groundwater in many of the states aquifer systems. These results have implications for identifying new opportunities for reallocation of surface water use to reduce groundwater pumping and improve water sustainability in the region. Seasonal fluctuations in surface water supply and water withdrawals for irrigation highlight the fact that the water system is under more stress during the summer season. This observation underscores the need for infrastructure for shortterm surface water storage in agricultural regions. The water budget analysis presented here can be useful for stakeholders in developing water management plans and can also help to inform the development of a water code that will enable Louisiana to successfully manage and conserve its water resources for the future

A Bayesian Framework to Unravel Food, Groundwater, and Climate Linkages: A Case Study from Louisiana

Advancing our understanding of the connections among groundwater, food, and climate is critical to meet global food demands while optimizing water resources usage. However, our understanding of the linkages among groundwater, food, and climate is still limited. Here, we offer a Bayesian framework to simulate crop yield at a regional scale and quantify its relationships and associated uncertainty with climate, groundwater, agricultural, and energy-related variables. We implemented the framework in the rice-producing regions of Louisiana from 1960-2015. To build a parsimonious model, we used a probability-based variable selection approach to detect the key drivers of rice yield. Rice yield increased, groundwater declined, and area planted declined or did not change over 56yrs. The number of irrigation wells, groundwater level, air temperature, and area planted were found to be the key drivers of rice yield. The regression coefficients showed that rice yield was positively related to groundwater level, and negatively related to area planted and the number of irrigation wells. The limited influence of N fertilizer was noted on rice yield for the period when fertilizer data were available. The inverse relationship between rice yield and area planted pointed to the adaption of efficient crop management practices that maintained or increased yield, despite the decline in area planted. The farmers\u27 ability to install irrigation wells during droughts sustained the yields over long-term but not short-term. This decline in rice yield in response to drought over the short-term might explain the negative relation between yield and irrigation wells. Overall, this work highlighted the uncertainty in relationships between rice yield and key drivers and quantified the intimate connection between food and groundwater. This work may have implications for managing two highly competing commodities (i.e., groundwater and food) in agricultural regions

Assessment of Corrosion Potential of Coarse Backfill Aggregates for Mechanically Stabilized Earth Walls

The service life of mechanically stabilized earth walls depends on the rate of corrosion of the metallic reinforcements used in their construction. The assessment of corrosion potential requires an accurate evaluation of pH, resistivity, and sulfate and chloride concentrations of aqueous solutions in contact with the surrounding aggregate. Highway agencies tend to use larger aggregates that contain only a small amount of fine material (passing the Number 40 sieve) in the backfill. Evaluation of the electrochemical parameters of coarse aggregates is challenging because traditional evaluation methods call for the use of fine material. In this study, the suitability of traditional soil characterization techniques for use with coarse aggregates was assessed through leaching experiments performed on coarse limestone and dolomite aggregates from six quarries in Texas. Chemical differences were isolated from size-related kinetic leaching effects by comparing the results from same-sized material collected in the field with material derived from the crushing of larger (≥ 3/8 in.) aggregates in the laboratory. The testing demonstrated that the fines collected from the field were enriched in chemicals that, when exposed to water, decreased pH and resistivity and increased sulfate concentrations compared with the bulk rock. This was likely the result of sulfur compounds in the atmosphere reacting with carbonate rocks to produce reactive surface layers that were mechanically abraded into the fines. This phenomenon could bias traditional soil testing results and, therefore, the assessment of corrosion potential. This study demonstrated that a more accurate assessment of the electrochemical parameters can be obtained by crushing the coarse material to meet testing size specifications

Improving the Total Organic Carbon Estimation of the Eagle Ford Shale with Density Logs by Considering the Effect of Pyrite

Pyrite is a common mineral with a higher density than most other minerals in the Eagle Ford Shale formation. Hence, if pyrite is not considered in the total organic carbon (TOC) estimation, based on density logs, it may lead to errors. In order to improve the accuracy of the TOC estimation, we propose an updated TOC estimation method that incorporates the concentration of pyrite and organic porosity. More than 15 m of Eagle Ford Shale samples were analyzed using Rock-Eval pyrolysis, X-ray fluorescence (XRF), and X-ray diffraction (XRD). TOC, elemental concentration, and mineralogical data were analyzed for a better understanding of the relationship between the concentration of TOC and pyrite content in the Eagle Ford formation. An updated petrophysical model—including parameters such as organic pores, solid organic matter, inorganic pores, pyrite, and inorganic rock matrix without pyrite—was built using the sample data from the Eagle Ford. The model was compared with Schmoker’s model and validated with the Eagle Ford field data. The results showed that the updated model had a lower root mean square error (RMSE) than Schmoker’s model. Therefore, it could be used in the future estimation of TOC in pyrite-rich formations

Water, Climate, and Social Change in a Fragile Landscape

We present here and in the companion papers an analysis of sustainability in the Middle Rio Grande region of the U.S.-Mexico border and propose an interdisciplinary research agenda focused on the coupled human and natural dimensions of water resources sustainability in the face of climate and social change in an international border region. Key threats to water sustainability in the Middle Rio Grande River region include: (1) increasing salinization of surface and ground water, (2) increasing water demand from a growing population in the El Paso/Ciudad Juarez area on top of an already high base demand from irrigated agriculture, (3) water quality impacts from agricultural, municipal, and industrial discharges to the river, (4) changing regional climate that portends increased frequency and intensity of droughts interspersed with more intensive rainfall and flooding events, and (5) disparate water planning and management systems between different states in the U.S. and between the U.S. and Mexico. In addition to these challenges, there is an increasing demand from a significant regional population who is (and has been historically) underserved in terms of access to affordable potable water. To address these challenges to water resources sustainability, we have focused on: (1) the determinants of resilience and transformability in an ecological/social setting on an international border and how they can be measured and predicted; and (2) the drivers of change ... what are they (climate, social, etc.) and how are they impacting the coupled human and natural dimensions of water sustainability on the border? To tackle these challenges, we propose a research agenda based on a complex systems approach that focuses on the linkages and feedbacks of the natural, built/managed, and social dimensions of the surface and groundwater budget of the region. The approach that we propose incorporates elements of systems analysis, complexity science, and the use of modeling tools such as scenario planning and back-casting to link the quantitative with the qualitative. This approach is unique for our region, as are our bi-national focus and our conceptualization of water capital . In particular, the concept of water capital provides the basis for a new interdisciplinary paradigm that integrates social, economic, and natural sectors within a systems framework in order to understand and characterize water resources sustainability. This proposed approach would not only provide a framework for water sustainability decision making for our bi-national region at the local, state, and federal levels, but could serve as a model for similar border regions and/or international rivers in arid and semi-arid regions in the Middle East, Africa, Asia, and Latin America

Chemical and structural analysis of an antibody folding intermediate trapped during glycan biosynthesis

Human IgG Fc glycosylation modulates immunological effector functions such as antibody-dependent cellular cytotoxicity and phagocytosis. Engineering of Fc glycans therefore enables fine-tuning of the therapeutic properties of monoclonal antibodies. The N-linked glycans of Fc are typically complex-type, forming a network of noncovalent interactions along the protein surface of the Cγ2 domain. Here, we manipulate the mammalian glycan-processing pathway to trap IgG1 Fc at sequential stages of maturation, from oligomannose- to hybrid- to complex-type glycans, and show that the Fc is structurally stabilized following the transition of glycans from their hybrid- to complex-type state. X-ray crystallographic analysis of this hybrid-type intermediate reveals that N-linked glycans undergo conformational changes upon maturation, including a flip within the trimannosyl core. Our crystal structure of this intermediate reveals a molecular basis for antibody biogenesis and provides a template for the structure-guided engineering of the protein-glycan interface of therapeutic antibodies

Fractionation of Cu, Fe, and Zn Isotopes during the Oxidative Weathering of Sulfide-Rich Rocks

We measured the Fe, Cu, and Zn isotopic compositions of the fluids generated during leaching experiments with pyrite-, chalcopyrite-, and sphalerite-rich rocks and with a sphalerite mineral separate. Our study demonstrates that the oxidative weathering of sulfide-rich rocks can produce substantial variations in Fe (-1.75 to + 1.0‰ Δ56Fesolution-pyrite rock) and Cu (0.0 to + 2.0‰ Δ65Cusolution-chalcopyrite rock) isotopes and small variations in Zn isotopes (0.0 to + 0.2‰ Δ66Znsolution-sphalerite) in the fluid phase relative to the rock. For the Fe and Cu systems we suggest that isotopic fractionation is caused by electron-exchange-driven (e.g., Fe(II)/Fe(III) and Cu(I)/Cu(II) redox) reactions at the surfaces of the sulfide minerals that occur during air and aqueous chemical reactions. Under acidic conditions, these reactions tend to enrich the fluid phase in the heavier Fe and Cu isotopes. However, under circumneutral pH conditions, the Fe isotopic composition in solution was controlled by the precipitation of Fe(III)-oxide phases, which enriched the solution in the lighter Fe isotopes. This investigation provides a preliminary framework for interpreting the impact of sulfide oxidation reactions on the distributions of stable Fe, Cu, and Zn isotopes in natural waters

Mobility of Ba, Sr, Se and as under Simulated Conditions of Produced Water Injection in Dolomite

The volume of petroleum produced water (PPW) has increased dramatically over the last decade. PPWs are rich in salts and often contain high concentrations of potentially toxic trace elements such as Barium (Ba), Strontium (Sr), Selenium (Se), and Arsenic (As) which, under the right circumstances, may contaminate freshwater supplies. To avoid these issues, PPW is frequently disposed of in subsurface aquifers such as the dolomitic Arbuckle Group in the state of Oklahoma, USA. This may not be a permanent solution if the injected PPW migrates within the disposal sites to ultimately reach conductive fault zones and/or existing wells with casing and/or cementing failures. In these cases the water could pose an environmental risk to potable groundwater. In order to understand the mobility of these elements under conditions similar to produced water injection, we conducted a series of batch sorption experiments. We investigated the effect of brine salinity and temperature on the sorption of Ba, Sr, Se, and As by dolomite. The results revealed that the sorption of the tested elements on dolomite did not substantially change with increasing salinity from 18 to 90 g/L. However, the sorption for all elements did increase with increasing temperature from 22 to 150 °C. This is likely due to a combination of strong surface complexation or ion exchange reactions coupled with precipitation/co-precipitation on the dolomite mineral surfaces

Dolomite Fronts and Associated Zinc-Lead Mineralization, USA

This paper provides previously unpublished drill core and mapping evidence of the spatial relationship between regional dolomitization and Mississippi Valley-type (MVT) mineralization in the midcontinent of the United States. Dolomitization is discussed for several key carbonate units and their contained MVT mineralization. This more complete picture of the relationship between regional dolomitization and mineralization provides constraints on models for MVT mineralization and serves as an exploration guide for new deposits