DEVELOPMENT OF A FRACTURED MEDIUM FLOW MODEL FOR A WASTE SITE1

ABSTRACT: A three‐dimensional fractured medium flow model was developed for the Bear Creek Valley (BCV) S‐3 site of the Oak Ridge Reservation (ORR) using SWIFT III. The numerical modeling for this site focused on a conceptual model established through the analysis of heterogeneous geologic units and matrix fracture properties of the subsurface in the BCV area. The SWIFT III modeling analysis was based on the previous modeling studies that used MODFLOW and MODPATH. A rigorous calibration was obtained first by comparing simulated results with the existing data on ground water levels and then by comparing pumping test results with the simulated ground water levels. A satisfactory agreement between observed and simulated results was obtained. The calibrated model was used to determine sustained yield from a ground water interceptor trench. Different withdrawal rates were used to simulate the performance of the trench for the sustained withdrawal of ground water.     

The Indian Ocean tsunami and private donations to NGOs

Non‐governmental organisations (NGOs) are widely believed to raise their flag in humanitarian hotspots with a strong media presence in order to attract higher private donations. We assess this hypothesis by comparing the changes in donations between US‐based NGOs with and without aid operations in the four countries most affected by the tsunami in the Indian Ocean in 2004. Simple before‐after comparisons tend to support the hypothesis that ‘flying the flag’ helps attract higher private donations. However, performing a difference‐in‐difference‐in‐differences (DDD) approach, we find only weak indications that private donors systematically and strongly preferred NGOs with operations in the region. Extended specifications of the baseline regressions reveal that our major findings are robust. NGO heterogeneity matters in some respects, but the DDD results hold when accounting for proxies of the NGOs’ reputation and experience.     

Altered ecohydrologic response drives native shrub loss under conditions of elevated nitrogen deposition

Many regions of southern California's coastal sage scrub (CSS) are rapidly declining as exotic annual plants replace native shrubs. During this conversion, the subsurface hydrology of the semiarid hillslopes that support CSS may be altered. This could chronically suppress the ability of native shrubland to revegetate the landscape since ecosystem processes of nutrient availability and of seedling establishment rely on spatial patterns of available soil water. In this work, soil water and nutrient N regimes were compared over a 2-yr period between a southern California site where CSS has declined (approximately 5% shrub cover) with high additions of anthropogenic N, and one where CSS remains dominant (over 50% shrub cover) with predominantly background atmospheric additions of N. These two sites have similar climate, bedrock lithology, soils, and topography, and had the same vegetation type (Riversidean CSS) 30 years ago. We found that the depth and rate of rainwater percolation into wildland hillslope soils in response to early-season storm events has been greatly reduced after loss of CSS shrubs and vegetation type conversion to invasive grassland. With decreased rainwater redistribution to soil depths of 100 to 150 cm, the predominant zone of soil water has become the upper 25 cm. This shift exacerbates vegetation type conversion by (i) concentrating smog-produced nitrogenous (N) chemicals in the uppermost soil, where they become readily available, along with high soil water, to shallow-rooted exotic grasses early in the growing season and (ii) depriving adult and juvenile shrubs of deeper regolith water.     

Spatial Patterns of Water Quality in the Cuiabá River Basin, Central Brazil

This study evaluates the spatial patterns of land occupation and their relationship to water quality in the Cuiabá River watershed, one of the main affluents of the Pantanal floodplain. The impact of farming and other land occupation forms were studied using a three year time series. Monitoring included 15 parameters at 21 stations with a total of 1266 different samples. Ten stations along the Cuiabá River were ordinated by Principal Component Analysis (PCA). For an exploratory analysis in the spatial domain, sub-basins of the Cuiabá watershed were classified according to mean concentrations of selected water quality parameters. Supervised classification of digital Landsat ETM imagery and standard GIS techniques were applied to parameterize land use and occupation according to a watershed scale. Redundancy Analysis (RDA) was then used to evaluate impacts of environmental and socio-economic factors on water quality.A Cuiabá headwater station only shows slightly elevated total coliform counts and concentrations of nutrients in the river after it passes regions of extensive cattle farming. After the confluence with the Manso River, nutrient and COD concentrations increase significantly, receiving loads from sub-basins under intensive agricultural land use, with mean annual concentrations up to 1.74 mg/L of total nitrogen (Kjedahl). Sub-watersheds with intensive fishing culture activities were shown to have significant impact on nitrogen concentrations, reaching mean concentrations of 2.66 mg/L of total nitrogen in the affluents. Most serious biological and chemical water pollution can be observed at stream outlets in the urban agglomeration of Cuiabá/Várzea Grande. Affluent pollution is reflected in the water quality of the Cuiabá River: subsequent monitoring stations in the urban area are ordinated on a gradient of increasing degradation of chemical and biological water quality. The auto-depuration capacity of the Cuiabá River is intact, but elevated concentrations of Phosphorous and Chemical Oxygen Demand can be observed as far away as the Pantanal floodplain, about 120 km downstream from the urban agglomeration.     

Bench-scale testing of a novel soil PFAS treatment train for informed remedial planning and decision-making

Bench-scale batch tests were conducted to assess the potential applicability of a combined separation/concentration/destruction treatment train to address soils and sediments impacted by per- and polyfluoroalkyl substances (PFAS) contamination at Schriever Space Force Base with historic aqueous film-forming foam (AFFF). Specifically, a novel treatment train coupling soil washing (for treatment of impacted soil/sediment) with foam fractionation (for treatment of the wash water [WW] generated during soil washing) and electrochemical oxidation (ECO, for treatment of the foam fractionate generated during foam fractionation) was evaluated at the bench scale using site-specific materials. Results presented herein show that the AFFF-impacted sandy soils with low organic content were amenable to treatment via soil washing. However, the removal of hydrophobic PFAS, such as perfluorooctanesulfonic acid (PFOS), from the organic-rich sediments was challenging. Results from batch desorption experiments were within a factor of 2 of those generated by soil washing bench studies, suggesting that simple batch tests can potentially be used to reasonably predict the treatment efficacy of soil washing. Long-chained perfluoroalkyl acids (PFAAs) within the WW were removed more effectively in the foam fractionation studies as compared to short-chain PFAAs. Addition of a surfactant, such as cetrimonium bromide (CTAB), enhanced foaming but only marginally improved the treatment of short-chained PFAAs and in some cases inhibited PFOS removal. ECO reduced PFAS concentrations in the foam fractionate generated during foam fractionation by several orders of magnitude. However, generation of unwanted byproducts may warrant further treatment and/or disposal. Overall, results from this study provide a novel data set highlighting the site-dependent nature of these PFAS remedial technologies and how simple, low-cost bench tests can be reliably leveraged for informed decision-making during PFAS remedial planning.     

The assimilation of contaminants from suspended sediment and algae by the zebra mussel, Dreissena polymorpha

Since their invasion into the Great Lakes, zebra mussels, Dreissena polymorpha, have increased the water clarity in Lake St. Clair and Lake Erie due to their extensive particle filtration. Because these particles contain sorbed contaminants, the potential for contaminant accumulation from both suspended sediment and algae were examined. Sediment or algae were dosed with selected radiolabeled polycyclic aromatic hydrocarbon congeners and/or hexachlorobiphenyl (HCBP). Assimilation efficiencies were measured and depended on food quality. Zebra mussels, 17 ± 2 mm long, assimilated 58.3 ± 13.5% of the pyrene and 44.7 ± 5.8% of the benzo(a)pyrene (BaP) from sediment particles with a particle clearance rate of 493 – 897 ml/g tissue/h. However, assimilation efficiencies were 91.7 ± 3.7% for pyrene, 91.9 ± 1.4% for BaP, 96.6 ± 1.4% for chrysene, and 97.7 ± 0.5% for HCBP from suspended algae. Algal particle clearance rates for the mussels ranged from 47 – 143 ml/g tissue/h. Thus, zebra mussels efficiently accumulated non-polar contaminants sorbed to algae, while a smaller fraction of the sediment-associated contaminant was bioavailable. Furthermore, the contaminants sorbed onto suspended sediment particles were quickly removed from the water and deposited as pseudofeces. The pseudofeces production was positively correlated with filtration rate and suspended particle concentrations.     

Phosphine by bio-corrosion of phosphide-rich iron

Phosphine is a toxic agent and part of the phosphorus cycle. A hitherto unknown formation mechanism for phosphine in the environment was investigated. When iron samples containing iron phosphide were incubated in corrosive aquatic media affected by microbial metabolites, phosphine was liberated and measured by gas chromatography. Iron liberates phosphine especially in anoxic aquatic media under the influence of sulfide and an acidic pH. A phosphine-forming mechanism is suggested: Phosphate, an impurity of iron containing minerals, is reduced abioticly to iron phosphide. When iron is exposed to the environment (e.g. as outdoor equipment, scrap, contamination in iron milled food or as iron meteorites) and corrodes, the iron phosphide present in the iron is suspended in the medium and can hydrolyze to phosphine. Phosphine can accumulate to measurable quantities in anoxic microbial media, accelerating corrosion and preserving the phosphine formed from oxidation.     

Climate change impacts on tree crop suitability in Southeast Asia

Regional Environmental Change - Understanding popular attitudes to climate change can be important in developing effective climate adaptation responses. However, in the Pacific region, which is at...     

Analysis of macroinvertebrate assemblages in relation to environmental gradients among lotic habitats of California's Central Valley

We assessed relationships between environmental characteristicsand macroinvertebrate assemblages in lotic habitats of California's Central Valley with community metric and multivariate statistical approaches. Using canonical ordinationanalyses, we contrasted results when assemblage structure was assessed with macroinvertebrate metrics, as suggested for use inindices of biotic integrity, or with genera abundances. Our objectives were to identify metrics or taxa diagnostic of loticenvironmental stressors and compare the capacity of theseapproaches to detect stressors in order to suggest how they mightbe used to diagnose stressors. For macroinvertebrate metrics,redundancy analysis (RDA) extracted three axes correlated withchannel morphology and substrates. For genera abundances, canonical correspondence analysis (CCA) extracted two axescorrelated with soluble salts and with channel morphology andsubstrates but did not separate these gradients onto differentaxes. Cluster analyses identified five RDA and five CCA sitegroups, which exhibited differences for environmental variables,metrics, or genera abundances, and agreement between the analysesin partitioning of sites was greater than if sites were partitioned randomly. These approaches differ in their abilityto detect environmental stressors, because they measure differentaspects of assemblages and would be complementary in design ofnew metrics diagnostic of stressors.     

Soil organic carbon storage in a mountain permafrost area of Central Asia (High Altai,Russia)

The thawing and subsequent decomposition of large stocks of soil organic carbon (SOC) currently stored in the northern circumpolar permafrost region are projected to result in a ‘positive’ feedback on global warming. The magnitude of this feedback can only be assessed with improved knowledge about the total size and geographic distribution of the permafrost SOC pool. This study investigates SOC storage in an under-sampled mountain permafrost area in the Russian High Altai. SOC stocks from 39 soil pits are upscaled using a GIS-based land cover classification. We found that the top 100 cm of soils in Aktru Valley and the adjacent Kuray Basin only holds on average 2.6 ± 0.6 kg C m⁻² (95% confidence interval), of which only c. 1% is stored in permafrost. Global warming will result in an upward shift of alpine life zones, with new plant cover and soil development at higher elevations. As a result, this type of mountain permafrost area might act as a net C sink in the future, representing a ‘negative’ feedback on global warming.Electronic supplementary materialThe online version of this article (10.1007/s13280-020-01433-6) contains supplementary material, which is available to authorized users.