Spatio-temporal log-Gaussian Cox processes for modelling wildfire occurrence: the case of Catalonia, 1994–2008

Wildfires have become one of the principal environmental problems in the Mediterranean basin. While fire plays an important role in most terrestrial plant ecosystems, the potential hazard that it represents for human lives and property has led to the application of fire exclusion policies that, in the long term, have caused severe damage, mainly due to the increase of fuel loadings in forested areas, in some forest systems. The lack of an easy solution to forest fire management highlights the importance of preventive tasks. The observed spatio-temporal pattern of wildfire occurrences may be idealized as a realization of some stochastic process. In particular, we may use a space–time point pattern approach for the analysis and inference process. We studied wildfires in Catalonia, a region in the north-east of the Iberian Peninsula, and we analyzed the spatio-temporal patterns produced by those wildfire incidences by considering the influence of covariates on trends in the intensity of wildfire locations. A total of 3,166 wildfires from 1994–2008 have been recorded. We specified spatio-temporal log-Gaussian Cox process models. Models were estimated using Bayesian inference for Gaussian Markov Random Field through the integrated nested Laplace approximation algorithm. The results of our analysis have provided statistical evidence that areas closer to humans have more human induced wildfires, areas farther have more naturally occurring wildfires. We believe the methods presented in this paper may contribute to the prevention and management of those wildfires which are not random in space or time.     

Characterizing vulnerability to water scarcity: The case of a groundwater-dependent,rapidly urbanizing region

Groundwater overdraft is a resource management issue that poses a threat for the security of communities. Impacts of groundwater overdraft are influenced by the biophysical and social contexts of water management. This paper presents a method for assessing vulnerability to water scarcity in spatial terms using biophysical and social indicators. A geographic information system was used to establish areas of vulnerability based upon hydrologic variability in water resource availability within a groundwater basin, three types of water management systems, and 10 sociodemographic characteristics. Our study area is in the rapidly urbanizing Arizona Central Highlands, located ~150km north of the Phoenix metropolitan region, USA. Results indicate that the most biophysically vulnerable places do not necessarily intersect with the most vulnerable populations and that local differences in vulnerability are interrelated, rather than independent, outcomes in a process of socioenvironmental transformation. Vulnerability is influenced by laws that deny access to local surface waters and lead to dependence on fossil groundwater, and by economic reliance on urbanization. Localities attempt to reduce vulnerability through the development of community water systems and the expansion of water frontiers. While such strategies may reduce local vulnerability, they are not sustainable solutions because they transfer risks to other places, and thus contribute to vulnerability elsewhere.     

Volatile organic compounds of Acacia longifolia and their effects on germination and early growth of species from invaded habitats

Acacia longifolia, a highly invasive species that invades coastal ecosystems in Mediterranean areas, produces significant impacts at different scales. Abundant foliage and thick canopies create a dense atmosphere that led us to hypothesise that the release of volatile organic compounds (VOCs) could play a role in the reduction of biodiversity observed in invaded areas. Therefore, we suggested that VOCs emitted by A. longifolia could exert inhibitory effects on physiological and biochemical parameters of native species. Using glass chamber bioassays, we evaluated the effect of aerial contact between VOCs from different plant parts of A. longifolia material and some native species. Volatile chemical composition was further analysed using GC-MS. Our results indicated that VOCs produced a notably reduction of seed germination. Furthermore, volatiles from leaves and flowers significantly decreased root length, shoot length and biomass for all species. Proline and malondialdehyde content did not significantly increase after contact with VOCs. Finally, chemical profile of VOCs from flowers, leaves and litter was significantly different, both qualitatively and quantitatively. As far as we know, our results constitute the first evidence of phytotoxicity induced by VOCs from A. longifolia, suggesting that flowers and leaves could influence its surrounding environment through VOCs release.     

Linking predator and prey behaviour: contrasts between Antarctic fur seals and macaroni penguins at South Georgia

Antarctic fur seals Arctocephalus gazella and macaroni penguins Eudyptes chrysolophus are the two main land-based krill Euphausia superba consumers in the northern Scotia Sea. Using a combination of concurrent at-sea (predator observations, net hauls and multi-frequency acoustics), and land-based (animal tracking and diet analysis) techniques, we examined variability in the foraging ecology of these sympatric top predators during the austral summer and autumn of 2004. Krill availability derived from acoustic surveys was low during summer, increasing in autumn. During the breeding season, krill occurred in 80% of fur seal diet samples, with fish remains in 37% of samples. Penguin diets contained the highest proportion of fish in over 20 years of routine monitoring (46% by mass; particularly the myctophid Electrona antarctica), with krill (33%) and amphipods (Themisto gaudichaudii; 21%) also occurring. When constrained by the need to return and feed their offspring both predator species foraged to the northwest of South Georgia, consistent with an area of high macrozooplankton biomass, but fur seals were apparently more successful at exploiting krill. When unconstrained by chick-rearing (during March) penguins foraged close to the Shag Rocks shelf-break, probably exploiting the high daytime biomass of fish in this area. Penguins and seals are able to respond differently to periods of reduced krill abundance (in terms of variability in diet and foraging behaviour), without detriment to the breeding success of either species. This highlights the importance of myctophid fish as an alternative trophic pathway for land-based predators in the Scotia Sea ecosystem.     

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.     

Size-mediated non-trophic interactions and stochastic predation drive assembly and dynamics in a seabird community

Theoretical and empirical evidence suggests that body size is a major life-history trait impacting on the structure and functioning of complex food webs. However, long-term analyses of size-dependent interactions within simpler network modules, for instance, competitive guilds, are scant. Here, we model the assembly dynamics of the largest breeding seabird community in the Mediterranean basin during the last 30 years. This unique data set allowed us to test, through a "natural experiment," whether body size drove the assembly and dynamics of an ecological guild growing from very low numbers after habitat protection. Although environmental stochasticity accounted for most of community variability, the population variance explained by interspecific interactions, albeit small, decreased sharply with increasing body size. Since we found a demographic gradient along a body size continuum, in which population density and stability increase with increasing body size, the numerical effects of interspecific interactions were proportionally higher on smaller species than on larger ones. Moreover, we found that the per capita interaction coefficients were larger the higher the size ratio among competing species, but only for the set of interactions in which the species exerting the effect was greater. This provides empirical evidence for long-term asymmetric interspecific competition, which ultimately prompted the local extinction of two small species during the study period. During the assembly process stochastic predation by generalist carnivores further triggered community reorganizations and global decays in population synchrony, which disrupted the pattern of interspecific interactions. These results suggest that the major patterns detected in complex food webs can hold as well for simpler sub-modules of these networks involving non-trophic interactions, and highlight the shifting ecological processes impacting on assembling vs. asymptotic communities.     

Tracking sewage derived contamination in riverine settings by analysis of synthetic surfactants

A study has been made of the presence and reactivity of the most commonly used surfactants, both anionic (linear alkylbenzene sulfonates, LAS, and alkyl ethoxysulfates, AES) and non-ionic (alcohol polyethoxylates, AEOs, and nonylphenol polyethoxylates, NPEOs), in water and surface sediments from the middle stretch of the Guadalete River in SW Spain (12 stations). Average values were between 0.1 and 3.7 mg kg(-1) in sediment, and between 0.2 and 37 μg L(-1) in water. The sorption of surfactants was dominated by hydrophobic mechanisms, so those homologues having longer alkyl chains (e.g. C(18)AEO) showed higher relative percentages and concentrations in sediments compared with water. Local and sharply higher concentrations of these compounds were observed at three sampling stations (7, 9 and 12), indicating the occurrence of wastewater discharges into the river. By analysing the distributions of different surfactant homologues and their metabolites we were able to distinguish between sewage contamination from sources discharging treated and untreated wastewaters. Upstream (stations 1-2), LAS concentrations were below 30 μg L(-1) and the composition of their degradation intermediates (sulfophenyl carboxylic acids, SPCs) (160 μg L(-1)) was dominated by short-chain homologues (C(6)-C(9)SPCs), indicating that the degradation of this surfactant is at an advanced stage. The highest concentration (487 μg L(-1)) of SPCs was detected near the effluent outlet of a sewage treatment plant (STP) (station 12). Sampling stations (7 and 9) affected by untreated wastewater discharges were the only ones showing the presence of the most reactive and biodegradable SPC isomers and homologues (e.g. C(11)SPC). Here, LAS reached the highest concentration values measured (>2 mg L(-1)), and showed a homologue distribution closer to that of commercial mixtures than LAS found at the other stations.     

Feather mercury levels in beached Magellanic penguin (Spheniscus magellanicus) in northern Argentina during the non-breeding season

Environmental Science and Pollution Research - Mercury (Hg) is a great concern for marine environments. Bird feathers have been widely used to assess Hg pollution. In this study, we determine...     

Is Diversification a Suitable Option to Reduce Drought-Induced Risk of Forest Dieback? An Economic Approach Focused on Carbon Accounting

Environmental Modeling & Assessment - Extreme or recurrent drought events are the principal source of stress on forests, impairing their overall health. They result in financial losses for...