Modeling Fate, Transport, and Biological Uptake of Selenium in North San Francisco Bay

Selenium behavior in North San Francisco Bay, the largest estuary on the US Pacific coast, is simulated using a numerical model. This work builds upon a previously published application for simulating selenium in the bay and considers point and non-point sources, transport and mixing of selenium, transformations between different species of selenium, and biological uptake by phytoplankton, bivalves, and higher organisms. An evaluation of the calibrated model suggests that it is able to represent salinity, suspended material, and chlorophyll a under different flow conditions beyond the calibration period, through comparison against long-term data, and the distribution of different species of dissolved and particulate selenium. Model-calculated selenium concentrations in bivalves compared well to a long-term dataset, capturing the annual and seasonal variations over a 15-year period. In particular, the observed lower bivalve concentrations in the wet flow periods, corresponding to lower average particulate selenium concentrations in the bay, are well represented by the model, demonstrating the role of loading and hydrology in affecting clam concentrations. Simulated selenium concentrations in higher organisms including white sturgeon and greater scaup also compared well to the observed data in the bay. Finally, a simulation of changing riverine inflows into the bay that might occur as a consequence of proposed hydrologic modifications indicated significant increases in dissolved and particulate selenium concentrations in the bay. The modeling framework allows an examination of the relationship between selenium loads, variations in inflow, in-bay concentrations, and biota concentrations to support management for limiting wildlife impacts.     

Perceptions of environmental change in Moorea,French Polynesia: the importance of temporal,spatial, and scalar contexts

Pacific Islands are considered among the most vulnerable geographies and societies to the effects of climate change and variability (CCV). This study addresses the mismatch between global climate change narratives and local perceptions of environmental change in Moorea, French Polynesia. This study builds on CCV risk perception and adaptation research by analyzing how temporal and historical socio-economic, cultural, political, and ecological contexts shape local perceptions of environmental change among a sample of environmental stakeholders in Moorea. The data were collected prior to the widespread global narrative and social amplification of climate change risk and its particular impact on islands. As such, they offer an important portrait of environmental perceptions in French Polynesia prior to the influence of a circumscribed climate change narrative, which has since come to shape government and NGO responses to environmental change in the Pacific Island Countries and Territories. The data presented in this paper illustrate that perceptions of drivers and effects of environmental change and risk in Moorea are embedded in larger social processes of political economy and ecology, particularly related to contemporary environmental politics, contextualized within the histories of colonialism and tourism-led economic development. Integrating the complexity of local environmental risk perceptions into CCV policy will help to avoid maladaptation, social movements against CCV planning, and may help maximize government and donor investments.     

Fine-Scale Detection of Estuarine Water Quality with Managed Freshwater Releases

Freshwater pulses to subtropical estuaries often occur on time scales less than 1 week. In particular, introduction of low-level pulses are potentially important during the dry season (November–April) when freshwater is scarce. Determining potential ecological benefits of pulses requires an innovative method of data acquisition at the appropriate spatial and temporal scales. The South Florida Water Management District conducted a pilot study to assess changes in water column attributes with pulse releases to the Caloosahatchee River Estuary (CRE) from January to April 2012. An average inflow of 450 cfs was targeted for a series of freshwater pulses. This study utilized an onboard, flow-through system to record surface water temperature, salinity (S), pH, dissolved oxygen, turbidity, and in situ chlorophyll a (in situ CHL) at 5 s intervals along the 42-km length of the estuary. On each of seven research cruises, the vessel stopped at multiple stations to conduct vertical water column profiles. Salinity increased throughout the CRE as inflow decreased during the study period. Simple correlation and partial least squares regression were used to determine that the downstream locations of the S?=?10 isohaline and the maximum CHL concentration (in situ CHL_max) were positively related to inflow. While the in situ CHL_max was located 12–20 km downstream on five of the cruises, it was only a few kilometer from the estuary head on the first (1/12) and last (4/11) dates. It is possible that two circumstances related to freshwater inflow accounted for this pattern. First, water column stratification before January could have stimulated remineralization and primary production. Second, inflow ceased as water temperature increased to 26.0 °C by April to promote algal growth. Further study of the relationships among inflow, water level, flushing time, and CHL is warranted. Future efforts will examine the range of wet season discharge by incorporating a sensor for colored dissolved organic matter to fully connect inflow, salinity, submarine light, and phytoplankton attributes in the CRE.     

A 108.83-m ice-core record of atmospheric dust deposition at Mt. Qomolangma (Everest), Central Himalaya

The central Himalaya can be regarded as an ideal site for developing a long-term ice core dust record to reflect the environmental signals from regional to semi-hemispheric scales. Here we present a dust record from segments of a 108.83-m ice core recovered from the East Rongbuk (ER) Glacier (27°59′N, 86°55′E; 6518 m a.s.l.) on the northeast slope of Mt. Qomolangma (Everest) in the central Himalaya, covering the period AD 600-1960. Due to rapidly layer thinning and coarse sampling, we primarily discuss the changes in the dust record since AD 1500 in this paper. Results show a significant positive relationship between the dust concentration and reconstructed air temperatures during this period, suggesting a likely cold-humid and warm-dry climatic pattern in the dust source regions, namely Central Asia. This is associated with the variability in the strength of the westerlies and its corresponding precipitation.     

Tracing the interaction of acid mine drainage with coal utilization byproducts in a grouted mine: Strontium isotope study of the inactive Omega Coal Mine,West Virginia (USA)

In order to ameliorate acidic discharge, the inactive Omega Coal Mine, West Virginia was partially filled by injection of a grout consisting of 98% coal utilization byproducts (CUB), including fluidized bed combustion ash and fly ash, and 2% Portland cement. In this study, discharge chemistry and Sr isotope ratios were determined to identify and quantify the extent of interaction between mine waters and the CUB–cement grout. Eight sampling sites were monitored around the downdip perimeter of the mine. The major and trace element chemistry of the discharges was generally not sufficient to distinguish between discharges that interacted with grout and those that did not. Elements that showed the most separation include K and As, which were elevated in some waters that interacted with CUB–cement grout. In contrast, the Sr isotope ratios clearly distinguished discharges from grouted and non-grouted areas. Discharges that bypassed the grouted portions had ⁸⁷Sr/⁸⁶Sr ratios ranging from 0.71510 to 0.71594, while two discharges that interacted with grout had ratios in the range of 0.71401–0.71456. The Treatment Inlet, which includes both grouted and ungrouted discharges, yielded intermediate isotopic ratios. Leaching experiments on CUB–cement grout, coal and surrounding rocks are consistent with the isotopic trends observed in the discharges. Based on these results, waters that interacted with grout received 30–40% of their Sr from the CUB–cement grout material. These results suggest that the grout material is chemically eroding at a rate of approximately 0.04% per year. This novel application of the Sr isotope system illustrates its ability to sensitively track and quantify fluid interaction with coal and CUB-based grout.     

Reducing long-term remedial costs by transport modeling optimization

The Department of Defense (DoD) Environmental Security Technology Certification Program and the Environmental Protection Agency sponsored a project to evaluate the benefits and utility of contaminant transport simulation-optimization algorithms against traditional (trial and error) modeling approaches. Three pump-and-treat facilities operated by the DoD were selected for inclusion in the project. Three optimization formulations were developed for each facility and solved independently by three modeling teams (two using simulation-optimization algorithms and one applying trial-and-error methods). The results clearly indicate that simulation-optimization methods are able to search a wider range of well locations and flow rates and identify better solutions than current trial-and-error approaches. The solutions found were 5% to 50% better than those obtained using trial-and-error (measured using optimal objective function values), with an average improvement of approximately 20%. This translated into potential savings ranging from 600,000 dollars to 10,000,000 dollars for the three sites. In nearly all cases, the cost savings easily outweighed the costs of the optimization. To reduce computational requirements, in some cases the simulation-optimization groups applied multiple mathematical algorithms, solved a series of modified subproblems, and/or fit "meta-models" such as neural networks or regression models to replace time-consuming simulation models in the optimization algorithm. The optimal solutions did not account for the uncertainties inherent in the modeling process. This project illustrates that transport simulation-optimization techniques are practical for real problems. However, applying the techniques in an efficient manner requires expertise and should involve iterative modification to the formulations based on interim results.     

Determination of particulate organic carbon (POC) in seawater: The relative methodological importance of artificial gains and losses in two glass-fiber-filter-based techniques

Particulate matter in aquatic systems is an important vehicle for the transport of particulate organic carbon (POC). Its accurate measurement is of central importance for the understanding of marine carbon cycling. Previous work has shown that GF/F-filter-based bottle-sample-derived concentration estimates of POC are generally close to or higher than large-volume in-situ-pump-derived values (and in some rare cases in subzero waters are up to two orders of magnitude higher). To further investigate this phenomenon, water samples from the surface and mid-water Northeast Atlantic and the Baltic Sea were analyzed. Our data support a bias of POC concentration estimates caused by adsorption of nitrogen-rich dissolved organic material onto GF/F filters. For surface-ocean samples the mass per unit area of exposed filter and composition of adsorbed material depended on the filtered volume. Amounts of adsorbed OC were enhanced in the surface ocean (typically 0.5 μmol cm^− 2 of exposed filter) as compared to the deep ocean (typically 0.2 μmol cm^− 2 of exposed filter). These dependencies should be taken into account for future POC methodologies. Bottle/pump differences of samples that were not corrected for adsorption were higher in the deep ocean than in the surface ocean. This discrepancy increased in summer. It is shown that POC concentration estimates that were not corrected for adsorption depend not only on the filtered volume, true POC concentration and mass of adsorbed OC, but also on the filter area. However, in all cases we studied, correction for adsorption was important, but not sufficient, to explain bottle/pump differences. Artificial formation of filterable particles and/or processes leading to filterable material being lost from and/or missed by sample-processing procedures must be considered. It can be deduced that the maximum amounts of POC and particulate organic nitrogen (PON) that can be artificially formed per liter of filtered ocean water are  3–4 μM OC (5–10% of dissolved OC) and  0.2–0.5 μM ON (2–10% of dissolved ON), respectively. The relative sensitivities of bottle and pump procedures, and of surface- and deep-ocean material, to artificial particle formation and the missing/losing of material are evaluated. As present procedures do not exist to correct for all possible biasing effects due to artificial particle formation and/or miss/loss of filterable material, uncertainties of filtration-based estimates of POC concentrations need further testing. The challenge now is to further constrain the magnitude of the biasing effects that add to the adsorption effect to reduce the uncertainties of estimates of POC concentrations, inventories and fluxes in the ocean.     

Release of Arsenic from Volcanic Rocks through Interactions with Inorganic Anions and Organic Ligands

The effects of a number of inorganic anions (F⁻, HCO₃ ⁻, B(OH)₄⁻, Cl⁻, I⁻) and of the siderophore DFO-B on the release of As from volcanic rocks were investigated in batch experiments. While previously reported field and laboratory data support a role of inorganic anions on As mobilization into aquifers, the role of siderophores on As-induced mobilization was less investigated. Fluoride, bicarbonate and DFO-B have shown a significant influence on the release of As from the rocks. Lava was mostly affected among the investigated rocks at pH 6 and 20°C by releasing 4% of its initial As content in the presence of 0.01 M F⁻and 10% in the presence of 500 μM DFO-B. The effect of fluoride was larger at pH 6 than at pH 8.5 for all the rocks. In the case of DFO-B, there was also a larger effect at pH 6 compared to pH 8 for the various rocks except tuff. Bicarbonate played a role under alkaline conditions while its effect was negligible at pH 6. Anion exchange processes in the presence of fluoride and bicarbonate and complexation processes in the presence of the siderophore DFO-B appear to be the major processes responsible for the release of arsenic from the rocks. The siderophore DFO-B plays mainly an indirect role on the As release by complexing Al, Fe and Mn, thus favoring the dissolution of the rocks and the consequent release of As bound to surface Al, Fe and Mn oxy-hydroxides. These findings suggest that ionic interactions with fluoride, bicarbonate and siderophore may be a further triggering factor in the mobilization of As from aquifer rocks.