Oxidation of acid-volatile sulfide in surface sediments increases the release and toxicity of copper to the benthic amphipod Melita plumulosa

Acid-volatile sulfides (AVS) are an important metal-binding phase in sediments. For sediments that contain an excess of AVS over simultaneously extracted metal (SEM) concentrations, acute or chronic effects should not result from the metals Cd, Cu, Ni, Pb and Zn. While AVS phases may exist in surface sediments, the exposure to dissolved oxygen may oxidize the AVS and release metals to more bioavailable forms. We investigated the role of oxidation of AVS, and specifically copper sulfide phases, in surface sediments, in the toxicity to juveniles of the epibenthic amphipod, Melita plumulosa. Sediments containing known amounts of copper sulfide were prepared either in situ by reacting dissolved copper with AVS that had formed in field sediments or created in sediments within the laboratory, or by addition of synthesised CuS to sediments. Regardless of the form of the copper sulfide, considerable oxidation of AVS occurred during the 10-d tests. Sediments that had a molar excess of AVS compared to SEM at the start of the tests, did not always have an excess at the end of the tests. Consistent with the AVS-SEM model, no toxicity was observed for sediments with an excess of AVS throughout the tests. However, the study highlights the need to carefully consider the changes in AVS concentrations during tests, and that measurements of AVS and SEM concentrations should carefully target the materials to which the organisms are being exposed throughout tests, which in the case of juvenile M. plumulosa is the top few mm of the sediments.     

Human–carnivore conflict: ecological and economical sustainability of predation on livestock by snow leopard and other carnivores in the Himalaya

Human communities in the Trans-Himalayan region depend on the dynamics of the agro-pastoral system for survival. Humans, livestock and wild predators share common resources in the region, and this leads to human–wildlife interactions that have the potential to threaten the continued viability of this fragile ecosystem and impact the local economy. This study explored the interaction between livestock and predators in the upper Mustang region of Nepal in terms of economic and ecological impacts. A total of 1,347 km² of pasture land were grazed by 30,217 livestock belonging to local people from six village development committees. It was found that the seasonal movement patterns of livestock, from higher to lower elevations (closer to villages), coincided with elevation movements of wild ungulate prey and snow leopards into this smaller land area. The number of livestock reported to have been killed by predators during the study period was 706, 75 % of which was attributed to snow leopards. An estimated US$ 44,213 was lost between October 2009 and June 2011 due to livestock predation. These losses of livestock to snow leopards and other carnivores provoked retaliatory killings by villagers, and this in turn may significantly affect the viability of predator populations in this region. We suggest four approaches to mitigate human–carnivore conflict in the region: (a) introduce a livestock insurance policy, (b) promote the use of predator-proof livestock corrals and sheds, (c) involve local people in alternative income generating activities, and (d) increase conservation education in these regions.     

Ecosystem responses to reduced and oxidised nitrogen inputs in European terrestrial habitats

While it is well established that ecosystems display strong responses to elevated nitrogen deposition, the importance of the ratio between the dominant forms of deposited nitrogen (NH_x and NO_y) in determining ecosystem response is poorly understood. As large changes in the ratio of oxidised and reduced nitrogen inputs are occurring, this oversight requires attention. One reason for this knowledge gap is that plants experience a different NH_x:NO_y ratio in soil to that seen in atmospheric deposits because atmospheric inputs are modified by soil transformations, mediated by soil pH. Consequently species of neutral and alkaline habitats are less likely to encounter high NH₄⁺ concentrations than species from acid soils. We suggest that the response of vascular plant species to changing ratios of NH_x:NO_y deposits will be driven primarily by a combination of soil pH and nitrification rates. Testing this hypothesis requires a combination of experimental and survey work in a range of systems.     

Rate-limited mass transfer of octane, decane, and dodecane into nonionic surfactants solutions under laminar flow conditions

A key component to predicting the success of utilizing surfactants to enhance the removal of organic liquids from soil system is quantifying micellar solubilization kinetics. In this study, a flow reactor was employed to investigate the influence of surfactant ethoxylate chain length on the rates of solubilization of octane, decane, and dodecane in micellar solutions of a homologous series of purified dodecyl alcohol ethoxylates. Effluent concentration data were fit using a finite element model utilizing a linear-driving-force model to represent mass transfer at the interface. For flow rates between 0.1 and 2 ml min(-1), mass transfer coefficients ranged from 5 x 10(-8) to 7 x 10(-7)m s(-1) and did not vary in a systematic way with either solute structure or surfactant ethoxylate chain length and were lower than those found in pure water. Correlations developed for the Sherwood number based on diffusion coefficients of surfactant micelles containing organic material (organic-laden micelle) exhibit a velocity dependence similar to that found for systems based on aqueous diffusion. These results suggest that under gentle flowing conditions, the mass transfer is limited by diffusion of the organic-laden micelle. Although these trends are specific for this experimental system, the results demonstrate the importance of selecting the proper diffusion coefficient when modeling surfactant solubilization processes.