Suppressing antagonistic bioengineering feedbacks doubles restoration success

In a seagrass restoration project, we explored the potential for enhancing the restoration process by excluding antagonistic engineering interactions (i.e., biomechanical warfare) between two ecosystem engineers: the bioturbating lugworm Arenicola marina and the sediment-stabilizing seagrass Zostera noltii Hornem. Applying a shell layer underneath half of our seagrass transplants successfully reduced adult lugworm density by over 80% and reduced lugworm-induced microtopography (a proxy for lugworm disturbance) at the wave-sheltered site. At the wave-exposed site adult lugworm densities and microtopography were already lower than at the sheltered site but were further reduced in the shell-treated units. Excluding lugworms and their bioengineering effects corresponded well with a strongly enhanced seagrass growth at the wave-sheltered site, which was absent at the exposed site. Enhanced seagrass growth in the present study was fully assigned to the removal of lugworms' negative engineering effects and not to any (indirect) evolving effects such as an altered biogeochemistry or sediment-stabilizing effects by the shell layer. The context-dependency implies that seagrass establishment at the exposed site is not constrained by negative ecosystem-engineering interactions only, but also by overriding physical stresses causing poor growth conditions. Present findings underline that, in addition to recent emphasis on considering positive (facilitating) interactions in ecological theory and practice, it is equally important to consider negative engineering interactions between ecosystem-engineering species. Removal of such negative interactions between ecosystem-engineering species can give a head start to the target species at the initial establishment phase, when positive engineering feedbacks by the target species on itself are still lacking. Though our study was carried out in a marine environment with variable levels of wave disturbance, similar principles may be expected to apply to other ecosystems that are inhabited by ecosystem engineers.     

Plant-mediated and nonadditive effects of two global change drivers on an insect herbivore community

Warmer temperatures can alter the phenology and distribution of individual species. However, differences across species may blur community-level phenological responses to climate or cause biotic homogenization by consistently favoring certain taxa. Additionally, the response of insect communities to climate will be subject to plant-mediated effects, which may or may not overshadow the direct effect of rising temperatures on insects. Finally, recent evidence for the importance of interaction effects between global change drivers suggests that phenological responses of communities to climate may be altered by other drivers. We used a natural temperature gradient (generated by elevation and topology), combined with experimental nitrogen fertilization, to investigate the effects of elevated temperature and globally increasing anthropogenic nitrogen deposition on the structure and phenology of a seminatural grassland herbivore assemblage (lepidopteran insects). We found that both drivers, alone and in combination, severely altered how the relative abundance and composition of species changed through time. Importantly, warmer temperatures were associated with biotic homogenization, such that herbivore assemblages in the warmest plots had more similar species composition than those in intermediate or cool plots. Changes in herbivore composition and abundance were largely mediated by changes in the plant community, with increased nonnative grass cover under high treatment levels being the strongest determinant of herbivore abundance. In addition to compositional changes, total herbivore biomass more than doubled under elevated nitrogen and increased more than fourfold with temperature, bearing important functional implications for herbivores as consumers and as a prey resource. The crucial role of nonnative plant dominance in mediating responses of herbivores to change, combined with the frequent nonadditive (positive and negative) effects of the two drivers, and the differential responses of species, highlight that understanding complex ecosystem responses will benefit from multifactor, multitrophic experiments at community scales or larger.     

Trophic cascade induced by molluscivore predator alters pore-water biogeochemistry via competitive release of prey

Effects of predation may cascade down the food web. By alleviating interspecific competition among prey, predators may promote biodiversity, but the precise mechanisms of how predators alter competition have remained elusive. Here we report on a predator-exclosure experiment carried out in a tropical intertidal ecosystem, providing evidence for a three-level trophic cascade induced by predation by molluscivore Red Knots (Calidris canutus) that affects pore water biogeochemistry. In the exclosures the knots' favorite prey (Dosinia isocardia) became dominant and reduced the individual growth rate in an alternative prey (Loripes lucinalis). Dosinia, a suspension feeder, consumes suspended particulate organic matter (POM), whereas Loripes is a facultative mixotroph, partly living on metabolites produced by sulfur-oxidizing chemoautotrophic bacteria, but also consuming suspended POM. Reduced sulfide concentrations in the exclosures suggest that, without predation on Dosinia, stronger competition for suspended POM forces Loripes to rely on energy produced by endosymbiotic bacteria, thus leading to an enhanced uptake of sulfide from the surrounding pore water. As sulfide is toxic to most organisms, this competition-induced diet shift by Loripes may detoxify the environment, which in turn may facilitate other species. The inference that predators affect the toxicity of their environment via a multi-level trophic cascade is novel, but we believe it may be a general phenomenon in detritus-based ecosystems.     

Fitting complex population models by combining particle filters with Markov chain Monte Carlo

We show how a recent framework combining Markov chain Monte Carlo (MCMC) with particle filters (PFMCMC) may be used to estimate population state-space models. With the purpose of utilizing the strengths of each method, PFMCMC explores hidden states by particle filters, while process and observation parameters are estimated using an MCMC algorithm. PFMCMC is exemplified by analyzing time series data on a red kangaroo (Macropus rufus) population in New South Wales, Australia, using MCMC over model parameters based on an adaptive Metropolis-Hastings algorithm. We fit three population models to these data; a density-dependent logistic diffusion model with environmental variance, an unregulated stochastic exponential growth model, and a random-walk model. Bayes factors and posterior model probabilities show that there is little support for density dependence and that the random-walk model is the most parsimonious model. The particle filter Metropolis-Hastings algorithm is a brute-force method that may be used to fit a range of complex population models. Implementation is straightforward and less involved than standard MCMC for many models, and marginal densities for model selection can be obtained with little additional effort. The cost is mainly computational, resulting in long running times that may be improved by parallelizing the algorithm.     

Sulfate pollution: evidence for electrochemical production of persulfate by oxidizing sulfate released by the surfactant sodium dodecyl sulfate

Environmental Chemistry Letters - There is increasing concern about contamination by surfactants that are used to extract organic pollutants during remediation of polluted soils and aquifers. For...     

In situ removal of arsenic from groundwater by using permeable reactive barriers of organic matter/limestone/zero-valent iron mixtures

In this study, two mixtures of municipal compost, limestone and, optionally, zero-valent iron were assessed in two column experiments on acid mine treatment. The effluent solution was systematically analysed throughout the experiment and precipitates from both columns were withdrawn for scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffractometry analysis and, from the column containing zero-valent iron, solid digestion and sequential extraction analysis. The results showed that waters were cleaned of arsenic, metals and acidity, but chemical and morphological analysis suggested that metal removal was not due predominantly to biogenic sulphide generation but to pH increase, i.e. metal (oxy)hydroxide and carbonate precipitation. Retained arsenic and metal removal were clearly associated to co-precipitation with and/or sorption on iron and aluminum (oxy)hydroxides. An improvement on the arsenic removal efficiency was achieved when the filling mixture contained zero-valent iron. Values of arsenic concentrations were then always below 10 μg/L.     

Spatial extremes of wildfire sizes: Bayesian hierarchical models for extremes

In Portugal, due to the combination of climatological and ecological factors, large wildfires are a constant threat and due to their economic impact, a big policy issue. In order to organize efficient fire fighting capacity and resource management, correct quantification of the risk of large wildfires are needed. In this paper, we quantify the regional risk of large wildfire sizes, by fitting a Generalized Pareto distribution to excesses over a suitably chosen high threshold. Spatio-temporal variations are introduced into the model through model parameters with suitably chosen link functions. The inference on these models are carried using Bayesian Hierarchical Models and Markov chain Monte Carlo methods.     

Effects of atrazine and nicosulfuron on freshwater microalgae

Growth modifications caused by various concentrations of atrazine and nicosulfuron were monitored in closed and continuous culture of Chlorella vulgaris (chlorophyta), Navicula accommoda (diatomophyta), and Oscillatoria limnetica (cyanophyta). The concentration at which algal growth rate was reduced twofold (EC50) was determined in the three species for both herbicides. Comparatively, the two toxicants were applied at 10 microg/l level in microcosms inoculated with natural phytoplankton from Lake Geneva. The relative abundances of major phytoplanktonic species were measured by algal cell count at the beginning and at the end of each experiment. Atrazine and nicosulfuron have different targets in plant metabolism, respectively, photosystem II (PSII) and acetolactate synthase (ALS), and the expected effects were different. Generally, the cultured phytoplankton exhibited various sensitivities, depending on species or herbicide. In the microcosms, the major taxa of natural phytoplanktonic samples exhibited various patterns, from acute toxicity to growth enhancement. For example, the diatoms inside the community were not affected by atrazine and nicosulfuron, except for Stephanodiscus minutulus that was sensitive to both, and Asterionella/formosa that was sensitive only to nicosulfuron. The specific physiology and the relationships among the phytoplanktonic communities have to be carefully considered when one would try to predict the extent of herbicide action on natural phytoplankton using in vitro tests. There is a need to test the toxic effect on various cultured strains, representative of most of the taxonomic composition of natural communities, to take into account the wide range of sensitivities and reaction to herbicide contamination. But this is not enough to give a solid frame when transposing the results to the field, and the use of more ecologically relevant systems is recommended.     

Reinforcement of Yeast Biomass Films with Bacterial Cellulose and Rice Husk Cellulose Nanofibres

Journal of Polymers and the Environment - In the last decades, cellulose nanoparticles have been widely used to reinforce polymeric materials due to their strength and their wide availability in...     

Recycling glass-polishing sludge and aluminum anodising sludge in polyurethane and cement composites: fire performance and mechanical properties

Journal of Material Cycles and Waste Management - This article aims to study the mechanical strength and fire resistance of polyurethane/cement (PuCem) composites containing glass sludge and sludge...