Natural attenuation of chlorinated solvent plumes at Texas dry cleaners

Dry cleaners are the largest users of perchloroethene (PCE) solvents in the United States. Releases from dry cleaners to soil and groundwater, however, remain largely unstudied. This article presents a database of 137 chlorinated solvent plumes at dry cleaners in Texas. The data indicate that PCE plumes are generally shorter in extent than those from industrial sites. Degradation products were observed at more than 80 percent of the sites with groundwater contamination. Calculated attenuation rates are on the order of one‐to‐three‐year half‐lives for PCE and its degradation products. The estimated cleanup timeframe for calculated attenuation rates is < 50 years. More research is needed to understand the presence of organic carbon sources at dry cleaners and its implications for natural attenuation. © 2004 Wiley Periodicals, Inc.     

Environmental impact assessment in the People's Republic of China: a case study of the Shanghai Second Sewerage Project

In March 1994, China announced its plans for sustainable development in a White Paper entitled 'China's Strategy for Population, Environment and Development in the 21st Century. To achieve the objective of sustainable development; economic, social and environmental aims have to be consistent with each other and meet the needs of the present, without compromising the ability of future generations to meet their own needs. Sustainable development, therefore, encompasses many 'ideals, which need to be introduced through practical management techniques. This paper addresses the role that EIA could play in promoting sustainable development projects in the People's Republic of China by way of the detailed examination of a case study—the Shanghai Second Sewerage Project.     

Using Steady‐State Backwater Analysis to Predict Inundated Area from National Water Model Streamflow Simulations

National Water Model (NWM) simulates the hydrologic cycle and produces streamflow forecasts for 2.7 million reaches in the National Hydrography Dataset for continental United States (U.S.). NWM uses Muskingum–Cunge channel routing, which is based on the continuity equation. However, the momentum equation also needs to be considered to obtain more accurate estimates of streamflow and stage in rivers, especially for applications such as flood‐inundation mapping. Here, we used a steady‐state backwater version of Simulation Program for River NeTworks (SPRNT) model. We evaluated SPRNT’s and NWM’s abilities to predict inundated area for the record flood of Hurricane Matthew in October 2016. The Neuse River experienced record‐breaking floods and was well‐documented by U.S. Geological Survey. Streamflow simulations from NWM retrospective analysis were used as input for the SPRNT simulation. Retrospective NWM discharge predictions were converted to stage. The stages (from both SPRNT and NWM) were utilized to produce flood‐inundation maps using the Height Above Nearest Drainage method which uses the local relative heights to find out the local draining potentials and provide spatial representation of inundated area. The inundated‐area accuracies for NWM and SPRNT (based on comparison to a remotely sensed dataset) were 65.1% and 67.6%, respectively. These results show using steady‐state SPRNT results in a modest improvement of inundation‐forecast accuracy compared to NWM.     

Prioritizing Stream Barrier Removal to Maximize Connected Aquatic Habitat and Minimize Water Scarcity

Instream barriers, such as dams, culverts, and diversions, alter hydrologic processes and aquatic habitat. Removing uneconomical and aging instream barriers is increasingly used for river restoration. Historically, selection of barrier removal projects used score‐and‐rank techniques, ignoring cumulative change and the spatial structure of stream networks. Likewise, most water supply models prioritize either human water uses or aquatic habitat, failing to incorporate both human and environmental water use benefits. Here, a dual‐objective optimization model identifies barriers to remove that maximize connected aquatic habitat and minimize water scarcity. Aquatic habitat is measured using monthly average streamflow, temperature, channel gradient, and geomorphic condition as indicators of aquatic habitat suitability. Water scarcity costs are minimized using economic penalty functions while a budget constraint specifies the money available to remove barriers. We demonstrate the approach using a case study in Utah's Weber Basin to prioritize removal of instream barriers for Bonneville cutthroat trout, while maintaining human water uses. Removing 54 instream barriers reconnects about 160 km of quality‐weighted habitat and costs approximately US$10 M. After this point, the cost‐effectiveness of removing barriers to connect river habitat decreases. The modeling approach expands barrier removal optimization methods by explicitly including both economic and environmental water uses.     

An assessment of toxicity in profundal lake sediment due to deposition of heavy metals and persistent organic pollutants from the atmosphere

A Tier I Sediment Ecological Risk Assessment of profundal lake sediment contaminated by diffuse pollution of heavy metals and POPs deposited from the atmosphere was completed. The concentrations of seven heavy metals and four groups of POPs (OCs, PCBs, PAHs, PBDEs) were determined in the profundal sediment of ten lakes in the United Kingdom and two sediment toxicity tests completed (chironomid survival and emergence and cladoceran survival and reproduction). The results showed that around half the lakes are at least moderately contaminated by Pb, Zn, Cd, As and PAHs deposited from the atmosphere and the toxicity quotient suggests that the contaminants of concern are Pb, As and PAHs, and not the other metals nor OCs and PCBs. There was toxicity in the sediment of four of the lakes. The Probable Effect Concentration Quotient values indicated that metals in the sediments of Scoat Tarn, Agden Reservoir and Llyn Llagi were likely to be responsible for the laboratory toxicity found in these lakes, with PAHs also contributing in Agden Reservoir.     

Effect of Forest Fragmentation on Genetic Diversity and Mating System in a Tropical Tree, Pithecellobium elegans

Genetic diversity, population differentiation, and temporal variation in outcrossing rates were examined for Pithecellobium elegans , a Neotropical rain forest canopy tree. Several forest fragments and a large reserve (1500 ha) were compared for several population genetic parameters. For eight populations sampled on the Atlantic coastal plain of Costa Rica, allozyme heterozygosity (0.13), polymorphism (35%), and effective number of alleles (1.24) were similar to values reported for other tropical tree species that occur at similar densities of less than one individual per hectare. These measures of genetic variation were lowest in populations of the smallest size, farthest from the reserve, and more isolated from other populations. Differentiation among samples collected in small forest fragments and the reserve population accounted for 10% of the total genetic variation observed. There was a positive relationship between the level of differentiation of populations from the reserve population and their distance from the reserve. Though predominantly an annually flowering species, the number of trees in flower at any one time varied from 80% of observed trees to only 6%. Outcrossing rates did not differ for two episodes in which the proportions of flowering trees were 33% and 80%. But periods of low density of flowering adults resulted in poor seed crops or failure to set fruit for many individuals. Population size at many sites will be effectively decreased because of the variation in flowering. Fragmentation of what was once a large, continuous forested area is resulting in genetic erosion of small, isolated populations of Pithecellobium elegans .     

Conversion from agriculture to grassland builds soil organic matter on decadal timescales.

Soil organic matter (SOM) often increases when agricultural fields are converted to perennial vegetation, yet decadal scale rates and the mechanisms that underlie SOM accumulation are not clear. We measured SOM accumulation and changes in soil properties on a replicated chronosequence of former agricultural fields in the midwestern United States that spanned 40 years after perennial-grassland establishment. Over this time period, soil organic carbon (SOC) in the top 10 cm of soil accumulated at a constant rate of 62.0 g x m(-2) x yr(-1), regardless of whether the vegetation type was dominated by C3 or C4 grasses. At this rate, SOC contents will be equivalent to unplowed native prairie sites within 55-75 years after cultivation ceased. Both labile (short turnover time) and recalcitrant (long turnover time) carbon pools increased linearly for 40 years, with recalcitrant pools increasing more rapidly than expected. This result was consistent across several different methods of measuring labile SOC. A model that investigates the mechanisms of SOM formation suggests that rapid formation of stable carbon resulted from biochemically resistant microbial products and plant material. Former agricultural soils of the Great Plains may function as carbon sinks for less than a century, although much of the carbon stored is stable.     

Brood neglect and contingent foraging behavior in a pelagic seabird

Among species where there is a risk to leaving offspring unattended, parents usually take alternating shifts guarding their young. However, they may occasionally exhibit brood neglect by leaving their offspring unattended at the nest. To investigate this phenomenon further, we examined the foraging behavior of the northern gannet (Morus bassanus) during chick-rearing. This species has a prolonged nestling period (13 weeks) and the single chick is usually guarded by one or other of its parents, because unattended chicks are frequently attacked by conspecifics. We tested the prediction that the foraging behavior of adults when they left their offspring alone at the nest (unattended trips) would differ in character to when adults left offspring with their partner (attended trips). Brood neglect typically occurred after a longer-than-average attendance period at the nest. Unattended trips were, on average, about half the duration of attended trips, and therefore much closer to the colony. There was also a difference in departure direction between attended and unattended trips, with unattended trips tending to be northeast of the colony. Chicks were fed by parents after both attended and unattended trips, but the frequency and the duration of unattended trips increased as chicks grew older whereas the duration of attended trips decreased as chicks grew. These results indicate that parents may be making a trade-off between risk of attack to their offspring and food-intake rate, and that the solution to this trade-off is dependent on chick age.Communicated by C. Brown     

Carbon Budget Implications of the Transition from Natural to Managed Disturbance Regimes in Forest Landscapes

Land-use change from an unmanaged to a managed forested landscape in northern forests is associated with a reduction of the area annually affected by natural disturbances (wildfires and forest insects) and the introduction of harvesting as a new disturbance. This study examined the impacts of changes in the disturbance regime-the frequency and type of disturbance-on landscape-level carbon (C) content and fluxes. The Carbon Budget Model of the Canadian Forest Sector was used to assess these impacts in six representative landscapes (100,000 ha each) with a range of disturbance regimes that are characteristic of conditions in coastal British Columbia, the interior of British Columbia, and the eastern boreal forest in Canada. The model was used to simulate ecosystem C fluxes during a period of natural disturbances, a 50-year transition period during which harvesting replaced natural disturbances, followed by 150 years of harvesting. The initial landscape-level biomass C content under natural disturbance regimes in the six example landscapes was 22 to 75% of their potential maximum content which is often used as the reference or baseline case. After 200 years of forest management, the C stored in the landscape plus the C retained in forest products manufactured from harvested biomass was between 58 and 101% of the landscape C content prior to the onset of harvesting. Landscape-level ecosystem C content was found to be affected by changes in the disturbance frequency, the age-dependence of the disturbance probabilities, and the disturbance-specific impacts on ecosystem C content. The results indicate that using the potential maximum C content of a landscape as the baseline always overestimates the actual C release due to land use change. A more meaningful procedure would be to assess the actual differences in landscape-level C content between the natural and the managed disturbance regime.