Understanding multiple ecological responses to anthropogenic disturbance: rivers and potential flow regime change

Human-induced alteration of the natural flow regime is a major threat to freshwater ecosystems and biodiversity. The effects of hydrological alteration on the structural and functional attributes of riverine communities are expected to be multiple and complex, and they may not be described easily by a single model. Based on existing knowledge of key hydrological and ecological attributes, we explored potential effects of a flow-regulation scenario on macroinvertebrate assemblage composition and diversity in two river systems in Australia's relatively undeveloped wet-dry tropics. We used a single Bayesian belief network (BBN) to model potential changes in multiple assemblage attributes within each river type during dry and wet seasons given two flow scenarios: the current, near-natural flow condition, and flow regulation. We then used multidimensional scaling (MDS) ordination to visually summarize and compare the most probable attributes of assemblages and their environment under the different scenarios. The flow-regulation scenario provided less certainty in the ecological responses of one river type during the dry season, which reduced the ability to make predictions from the BBN outputs directly. However, visualizing the BBN results in an ordination highlighted similarities and differences between the scenarios that may have been otherwise difficult to ascertain. In particular, the MDS showed that flow regulation would reduce the seasonal differentiation in hydrology and assemblage characteristics that is expected under the current low level of development. Our approach may have wider application in understanding ecosystem responses to different river management practices and should be transferred easily to other ecosystems or biotic assemblages to provide researchers, managers, and decision makers an enhanced understanding of ecological responses to potential anthropogenic disturbance.     

Comparative Water Quality of Lightly- and Moderately-Impacted Streams in the Southern Blue Ridge Mountains, USA

For less-developed regions like the Blue Ridge Mountains, data are limited that link basin-scale land use with stream quality. Two pairs of lightly-impacted (90–100% forested) and moderately-impacted (70–80% forested) sub-basins of the upper Little Tennessee River basin in the southern Blue Ridge were identified for comparison. The pairs contain physically similar stream reaches, chosen for the purpose of isolating forest conversion as a potential driver of any detected differences in water quality. Streams were sampled during baseflow conditions twice monthly over a six-month period from September 2003 through February 2004. Parametric t-tests were run for each parameter measured between the lightly-and moderately-impacted streams within each pair. Statistically significantly higher mean values of suspended and dissolved solids, nitrate, specific conductivity, turbidity, and temperature were observed in the moderately impacted streams versus the lightly impacted streams in both pairs, while dissolved oxygen levels were lower in the moderately-impacted streams. No significant differences were demonstrated in orthophosphate or ammonium concentration. A near-bankfull runoff event on February 6, 2004, was sampled for stormflow values, and the results support baseflow findings. The water quality of these streams is very good when compared with lower relief areas like the Piedmont, and none of the parameters measured in this study exceeds levels of known threat to stream biota. However, the demonstration that moderate reductions in forest cover are associated with stream water quality degradation carries important implications for stream management in this rapidly developing mountainous region.     

Assessing the potential for rhizoremediation of PCB contaminated soils in northern regions using native tree species

Rhizosphere bioremediation of polychlorinated biphenyls (PCBs) offers a potentially inexpensive approach to remediating contaminated soils that is particularly attractive in remote regions including the Arctic. We assessed the abilities of two tree species native to Alaska, Salix alaxensis (felt-leaf willow) and Picea glauca (white spruce), to promote microbial biodegradation of PCBs via the release of phytochemicals upon fine root death. Crushed fine roots, biphenyl (PCB analogue) or salicylate (willow secondary compound) were added to microcosms containing soil spiked with PCBs and resultant PCB disappearance, soil toxicity and microbial community changes were examined. After 180 d, soil treated with willow root crushates showed a significantly greater PCB loss than untreated soils for some PCB congeners, including the toxic congeners, PCB 77, 105 and 169, and showed a similar PCB loss pattern (in both extent of degradation and congeners degraded) to biphenyl-treated microcosms. Neither P. glauca (white spruce) roots nor salicylate enhanced PCB loss, indicating that biostimulation is plant species specific and was not mediated by salicylate. Soil toxicity assessed using the Microtox bioassay indicated that the willow treatment resulted in a less toxic soil environment. Molecular microbial community analyses indicated that biphenyl and salicylate promoted shifts in microbial community structure and composition that differed distinctly from each other and from the crushed root treatments. The biphenyl utilizing bacterium, Cupriavidus spp. was isolated from the soil. The findings suggest that S. alaxensis may be an effective plant for rhizoremediation by altering microbial community structure, enhancing the loss of some PCB congeners and reducing the toxicity of the soil environment.     

Strategies for enhancing the phytoremediation of cadmium-contaminated agricultural soils by Solanum nigrum L

Field trials contribute practical information towards the development of phytoremediation strategies that cannot be provided by laboratory tests. We conducted field experiments utilizing the Cd hyperaccumulator plant Solanum nigrum L., on farmland contaminated with 1.91 mg kg⁻¹ Cd in the soil. Our study showed that S. nigrum has a relatively high biomass. Planting density had a significant effect on the plant biomass and thus on overall Cd accumulation. For double harvesting, an optimal cutting position influenced the amount of Cd extracted from soils. Double cropping was found to significantly increase the amount of Cd extracted by S. nigrum. Fertilizing had no significant effect on plant biomass or on the Cd remediation of the soil over the short-term period. Our study indicates that S. nigrum can accumulate Cd from soils where the concentrations are relatively low, and thus has application for use in decontamination of slightly to moderately Cd-contaminated soil.     

A Benefit‐Cost Analysis of Total Maximum Daily Load Implementation1

Abstract: Total Maximum Daily Load (TMDL) implementation generates benefits and costs from water quality improvements, which are rarely quantified. This analysis examines a TMDL written to address bacteria and aquatic‐life‐use impairments on Abrams and Opequon Creeks in Virginia. Benefits were estimated using a contingent valuation survey of local residents. Costs were based on the number and type of best management practices (BMPs) necessary to achieve TMDL pollution reduction goals. BMPs were quantified using watershed‐scale water quality simulation models (Generalized Watershed Loading Function and Hydrological Simulation Program‐FORTRAN). Based on our projections, the costs to achieve TMDL induced pollution reduction goals outweigh the estimated benefits. Benefit‐cost ratios ranged between 0.1 and 0.3.     

Effective monitoring of agriculture: a response

The development of effective agricultural monitoring networks is essential to track, anticipate and manage changes in the social, economic and environmental aspects of agriculture. We welcome the perspective of Lindenmayer and Likens (J. Environ. Monit., 2011, 13, 1559) as published in the Journal of Environmental Monitoring on our earlier paper, "Monitoring the World's Agriculture" (Sachs et al., Nature, 2010, 466, 558-560). In this response, we address their three main critiques labeled as 'the passive approach', 'the problem with uniform metrics' and 'the problem with composite metrics'. We expand on specific research questions at the core of the network design, on the distinction between key universal and site-specific metrics to detect change over time and across scales, and on the need for composite metrics in decision-making. We believe that simultaneously measuring indicators of the three pillars of sustainability (environmentally sound, social responsible and economically viable) in an effectively integrated monitoring system will ultimately allow scientists and land managers alike to find solutions to the most pressing problems facing global food security.     

Field‐scale evaluation of a biobarrier for the treatment of a trichloroethene plume

In the 1960s, trichloroethene (TCE) was used at what is now designated as Installation Restoration Program Site 32 Cluster at Vandenberg Air Force Base to flush missile engines prior to launch and perhaps for other degreasing activities, resulting in releases of TCE to groundwater. The TCE plume extends approximately 1 kilometer from the previous launch facilities beyond the southwestern end of the site. To limit further migration of TCE and chlorinated degradation by‐products, an in situ, permeable, reactive bioremediation barrier (biobarrier) was designed as a cost‐effective treatment technology to address the TCE plume emanating from the source area. The biobarrier treatment would involve injecting carbon‐based substrate and microbes to achieve reductive dechlorination of volatile organic compounds, such as TCE. Under reducing conditions and in the presence of certain dechlorinating microorganisms, TCE degrades to nontoxic ethene in groundwater. To support the design of the full‐scale biobarrier, a pilot test was conducted to evaluate site conditions and collect pertinent design data. The pilot test results indicated possible substrate delivery difficulties and a smaller radius of influence than had been estimated, which would be used to determine the final biobarrier well spacing. Based on these results, the full‐scale biobarrier design was modified. In January 2010, the biobarrier was implemented at the toe of the source area by adding a fermentable substrate and a dechlorinating microbial culture to the subsurface via an injection well array that spanned the width of the TCE plume. After the injections, the groundwater pH in the injection wells continued to decrease to a level that could be detrimental to the population of Dehalococcoides in the SDC‐9^TM culture. In addition, 7 months postinjection, the injection wells could not be sampled due to fouling. Cleaning was required to restore their functions. Bioassay and polymerase chain reaction analyses were conducted, as well as titration tests, to assess the need for biobarrier amendments in response to the fouling issues and low pH. Additionally, slug tests were performed on three wells to evaluate possible localized differences in hydraulic conductivity within the biobarrier. Based on the test results, the biobarrier was amended with sodium carbonate and inoculated a second time with SDC‐9^TM. The aquifer pH was restored, and reductive dechlorination resumed in the treatment zone, evidenced by the reduction in TCE and the increase in degradation products, including ethene. © 2011 Wiley Periodicals, Inc.     

Alkyl nitrate photochemistry during the tropospheric organic chemistry experiment

Alkyl nitrates (C₁–C₅) were measured at two sites (near urban and rural) in southeast England during the Tropospheric Organic Chemistry Experiment (TORCH). Methyl nitrate was the dominant species during both campaigns accounting for on average about one third of the total measured alkyl nitrates. High mixing ratios (>50 pptv) and variability of methyl nitrate were observed at the near urban site (TORCH1) that were not seen at the rural site (TORCH2) and which could not be explained by local photochemical production or direct emissions. The diurnal variation of methyl nitrate during TORCH1 showed a morning maximum that would be consistent with nighttime chemistry followed by transport to the surface by boundary layer dynamics. Similarly, elevated morning mixing ratios were also observed during TORCH2 although the magnitudes were much smaller. As a result, methyl nitrate could represent a tracer for nighttime chemistry seen at the ground the following day. At both campaigns, the dominant source of short chain alkyl nitrates and carbonyl precursor radicals (≤C₄) were from decomposition of larger compounds. The magnitude of the source increased with decreasing carbon number consistent with increasing total precursor abundance. Non-photochemical emissions of acetaldehyde and acetone could not be accounted for by automobile exhaust emissions alone and indicated that other direct sources are likely important in this environment.     

Attenuation of polycyclic aromatic hydrocarbons from urban stormwater runoff by wood filters

A significant amount of contamination enters water bodies via stormwater runoff and, to reduce the amount of pollution, retention ponds are installed at many locations. While effective for treating suspended solids, retention ponds do not effectively remove dissolved constituents, such as polycyclic aromatic hydrocarbons (PAH). Previous laboratory studies demonstrates that aspen wood cuttings can be utilized to enhance the removal of dissolved contaminants. The objective of this pilot-scale field test was to determine if wood filters could effectively remove dissolved PAH from the runoff under field conditions. Four wood filter tests were conducted, lasting from 1 to 9 weeks, to determine the degree of PAH attenuation from the aqueous phase as a function of wood mass, residence times, and seasonable changes. The prototype wood filters removed on average between 18.5% and 35.6% (up to 66.5%) of the dissolved PAH contaminants. The PAH removal effectiveness of the wood was not affected by changes in water temperature or pH. The filter effectiveness increased with filter size and was highest in continuously submerged parts of the filter system. Also, heavier molecular weight PAH compounds (e.g. chrysene) were more effectively removed than lighter molecular weight compounds. Disassociation of weakly particle-bound PAH from the filter was identified as the most likely cause for a temporary drop of the wood filter's PAH load during intense storms. Simple filter design changes are likely to double the filter effectiveness and alleviate the disassociation problem.