Chemical and Biological Reduction of PCE by Pneumatic Fracturing and Injection of ZVI in Saprolite

This article presents a case study of the source‐area treatment of tetrachloroethene (PCE) in a low‐permeability formation using zero‐valent iron (ZVI). Evidence of the stimulation of biological reduction processes within the treatment zone occurred. Pneumatic fracturing and injection of microscale ZVI slurry in the overburden and weathered bedrock zones was performed at a commercial brownfields redevelopment site in Maryland. A 20,000‐square‐foot source area impacted with PCE at concentrations greater than 15,000 µg/L was treated at depths ranging from 10 to 70 feet bgs. An average ZVI dosage of 0.0024 iron‐to‐soil mass ratio within the overburden zone led to a 75 percent decrease in PCE mass in less than one year. For the weathered bedrock zone, an average 0.0045 iron‐to‐soil mass ratio resulted in a 92 percent decrease in PCE mass during the same period. The reducing environment and hydrogen generated by the ZVI may have stimulated Dehalobacter populations, as evidenced by concentrations up to 10⁴ cells per milliliter measured within the treatment area despite a groundwater pH as high as 9. The biological reductive dechlorination of the chlorinated ethenes explains the temporary increase in trichloroethene and cis‐1,2‐dichloroethene concentrations. © 2013 Wiley Periodicals, Inc.     

Use of Seawater in Flue Gas Desulfurization

For seasite power plants using seawater for condenser cooling, Bechtel developed a new process to remove better than 90 percent of flue gas SO₂ using seawater and lime. Tests demonstrate that marine life is not affected by the effluent from this unique scrubbing process; therefore, the aqueous effluent containing reacted products (gypsum) in solution at low concentration is suitable for discharge to the sea.     

Revisiting the classics: considering nonconsumptive effects in textbook examples of predator-prey interactions

Predator effects on prey dynamics are conventionally studied by measuring changes in prey abundance attributed to consumption by predators. We revisit four classic examples of predator-prey systems often cited in textbooks and incorporate subsequent studies of nonconsumptive effects of predators (NCE), defined as changes in prey traits (e.g., behavior, growth, development) measured on an ecological time scale. Our review revealed that NCE were integral to explaining lynx-hare population dynamics in boreal forests, cascading effects of top predators in Wisconsin lakes, and cascading effects of killer whales and sea otters on kelp forests in nearshore marine habitats. The relative roles of consumption and NCE of wolves on moose and consequent indirect effects on plant communities of Isle Royale depended on climate oscillations. Nonconsumptive effects have not been explicitly tested to explain the link between planktonic alewives and the size structure of the zooplankton, nor have they been invoked to attribute keystone predator status in intertidal communities or elsewhere. We argue that both consumption and intimidation contribute to the total effects of keystone predators, and that characteristics of keystone consumers may differ from those of predators having predominantly NCE. Nonconsumptive effects are often considered as an afterthought to explain observations inconsistent with consumption-based theory. Consequently, NCE with the same sign as consumptive effects may be overlooked, even though they can affect the magnitude, rate, or scale of a prey response to predation and can have important management or conservation implications. Nonconsumptive effects may underlie other classic paradigms in ecology, such as delayed density dependence and predator-mediated prey coexistence. Revisiting classic studies enriches our understanding of predator-prey dynamics and provides compelling rationale for ramping up efforts to consider how NCE affect traditional predator-prey models based on consumption, and to compare the relative magnitude of consumptive and NCE of predators.     

Maximal yields from multispecies fisheries systems: rules for systems with multiple trophic levels.

Increasing centralization of the control of fisheries combined with increased knowledge of food-web relationships is likely to lead to attempts to maximize economic yield from entire food webs. With the exception of predator-prey systems, we lack any analysis of the nature of such yield-maximizing strategies. We use simple food-web models to investigate the nature of yield- or profit-maximizing exploitation of communities including two types of three-species food webs and a variety of six-species systems with as many as five trophic levels. These models show that, for most webs, relatively few species are harvested at equilibrium and that a significant fraction of the species is lost from the web. These extinctions occur for two reasons: (1) indirect effects due to harvesting of species that had positive effects on the extinct species, and (2) intentional eradication of species that are not themselves valuable, but have negative effects on more valuable species. In most cases, the yield-maximizing harvest involves taking only species from one trophic level. In no case was an unharvested top predator part of the yield-maximizing strategy. Analyses reveal that the existence of direct density dependence in consumers has a large effect on the nature of the optimal harvest policy, typically resulting in harvest of a larger number of species. A constraint that all species must be retained in the system (a "constraint of biodiversity conservation") usually increases the number of species and trophic levels harvested at the yield-maximizing policy. The reduction in total yield caused by such a constraint is modest for most food webs but can be over 90% in some cases. Independent harvesting of species within the web can also cause extinctions but is less likely to do so.     

What is a static head measurement? Evaluating structural error and implications for regional groundwater modeling

Most groundwater modelers avoid using static heads measured from active production wells because they can introduce a bias into model calibration. However, in the deep confined Cambrian-Ordovician Sandstone Aquifer System in the Central Midcontinent of North America, dedicated observation wells are sparse and remote from areas of most concentrated pumping. As a result, in areas where drawdown is the greatest and modeling is most needed, only static heads from production wells are available for calibration. This paper evaluates two leading sources of discrepancies in using production well data, spatial and temporal structural error (S.E.). A simple Theis solution is used to evaluate the potential magnitude of spatial S.E. when calibrating a regional MODFLOW model with coarse cell resolution. Despite theoretical analyses indicating that spatial S.E. could be significant, statistical analysis of the model results suggests that temporal S.E. is dominant. Long (ranging over decades) or frequent (monthly) head datasets are key in understanding temporal S.E., to better capture water-level variability. In this study, the range in static head observations impacted estimates of the remaining time a well could extract water from the aquifer by 0.1 to 16.0 years. This uncertainty in future water supply is highly relevant to stakeholders and must be assessed in hydrographs depicting risk.     

Community wildfire protection planning in the American West: homogeneity within diversity?

As large wildfires have become common across the American West, federal policies such as the Healthy Forests Restoration Act have empowered local communities to plan for their own wildfire protection. Here, we present an analysis of 113 community wildfire protection plans from 10 western states where large fires have recently occurred. These plans contain wide diversity in terms of specific plan elements and dimensions, yet less diversity in the paradigms underlying their fire protection approaches. These patterns held true across both plans constructed solely by local actors as well as those constructed with the help of outside consultant expertise.     

Calibrating a model to 30 years of data to capture the accumulation of chloride from winter deicers in a shallow aquifer

Winter deicers are a major source of chloride contamination to shallow aquifers in northern latitudes. In the greater Chicago area of northeast Illinois, chloride has been accumulating for decades and in many places now exceeds the United States Environmental Protection Agency secondary standard of 250 mg/L. MODFLOW-NWT and MT3D-USGS were used to simulate the accumulation of chloride with 30 years of data in the shallow aquifer of Will County in northeast Illinois. This aquifer is composed of unconsolidated sediments, largely from glacial deposits, overlying a fractured dolomite bedrock. To calibrate to observed heads and chloride, the model needed refined geologic features, higher chloride concentrations on cells representing commercial or industrial lands, lower chloride concentrations on cells representing roads, and point source areas to speed chloride's emergence in the aquifer. These point sources are locally significant and could represent different anthropogenic or geologic features, such as municipal stormwater infrastructure. Future simulations indicate that chloride is not at steady state in the shallow aquifer and wells are at risk of exceeding the secondary standard if winter deicing applications are not reduced. It may take decades for the full impacts of reduced deicing rates to be observed in wells, owing to the long residence time of water in the aquifer. This transient model calibration was possible because of the 30-year dataset collected by communities and government agencies.     

Recognizing loss of open forest ecosystems by tree densification and land use intensification in the Midwestern USA

Regional Environmental Change - Forests and grasslands have changed during the past 200 years in the eastern USA, and it is now possible to quantify loss and conversion of vegetation cover...