Habitat Mosaic, Wildlife Availability, and Hunting in the Tropical Forest of Calakmul, Mexico

Abstract: Habitat loss and subsistence hunting are two of the main activities that affect wildlife in frontier areas. We compared subsistence hunting patterns in four villages with different ethnic composition and degree of habitat disturbance in the vicinity of Calakmul Biosphere Reserve, Campeche, Mexico. We also compared differences between some of these villages in harvest composition and prey availability to determine hunting preferences. We used a Landsat TM satellite image to analyze the degree of disturbance around the villages. We conducted periodic surveys of subsistence hunting and prey availability. Wildlife availability was assessed monthly on nine transects (3000 m) established in the vicinity of three villages. The relative amount of disturbed habitat was smaller in an indigenous Maya village ( IV ) and larger in a mestizo village ( MV ). The two mixed-composition villages ( MCVs) had intermediate levels of disturbance. Ten species, four large and six small, of birds and mammals accounted for 97% of the hunting records. Hunting was more intense in IV and less intense in MCV1. The three village types had different hunting preferences. The habitat-mosaic composition in the vicinity of the villages influenced prey availability and subsistence-hunting preferences. Changes in the habitat mosaic were caused by the size of the holding and by ethnic composition. In spite of longer settlement time, the habitat mosaic in the vicinity of IV was less transformed than that of the other sites. Their larger holding size and greater diversity of economic activities may explain why the Mayas at IV have transformed the landscape less than the other groups and can hunt more and larger prey.     

Are native naiads more tolerant to pollution than exotic freshwater bivalve species? An hypothesis tested using physiological responses of three species transplanted to mercury contaminated sites in the Ebro River (NE, Spain)

In the lower Ebro River exist the paradoxical convergence of relatively well preserved river dynamics with the historical presence of a chloralkali plant with a long history of mercury discharges and the recent invasion of foreign bivalves species. Here we performed a comparative study on two alien bivalves, the Zebra mussel and the Asian clam (Dreissena polymorpha and Corbicula fluminea), and one protected species of naiads (Psilunio littoralis), which is the most common species of the freshwater mussel assemblages in this river. Individuals of the three species were transplanted to three sites that included a clean unpolluted upstream site, a contaminated location next to the mercury source and a downstream one. The study focused on digestive gland antioxidant and oxidative stress responses such as antioxidant enzymes, glutathione S transferase, glutathione levels, metallothionein proteins, DNA strand breaks and lipid peroxidation levels. Results evidenced interspecies differences on accumulation levels of mercury, antioxidant defensive systems and oxidative tissue damage. The naiad species, despite of accumulating more mercury showed the greatest antioxidant defensive potential, which was characterized by having high constitutive activities of glutathione S transferase and inducible activities and levels of key antioxidant enzymes and glutathione. Exposed individuals of C. fluminea had moderate levels of metal accumulation, the highest activities of antioxidant enzymes but also high levels of lipid peroxidation. D. polymorpha mussels showed the lowest levels of mercury but the lowest antioxidant responses and consequently the highest levels of oxidative injuries in the DNA and of mortality. Our results support the hypothesis that naiad species might be more tolerant to pollution than exotic species.     

Influence of sediment acidification on the bioaccumulation of metals in Ruditapes philippinarum

Background, aim and scope

The influence of pH (range 6.5–8.5) on the uptake of Zn, Cd, Pb, Cu, Ni, Cr, Hg, and As by juveniles of the clam Ruditapes philippinarum was examined in order to understand whether variation in sediment pH has significant repercussions on metal bioaccumulation.

Materials and methods

Clams were exposed to sediments collected in three locations in the Gulf of Cadiz (Huelva, Guadalquivir and Bay of Cadiz) and to contaminated particles derived from an accidental mining spill in Spain.

Results

With a notable exception of metal Cd, the concentration of metals within clams significantly increased (p?<?0.1) when sediment pH was lowered by one or two units. Moreover, the magnitude of this effect was dependent on the type of sediment contamination.

Discussion

Lower pH increases metal solubility and reduces or invert the metal sorption of metals to sediments. Increases in free metal ions in water favors metal uptake by clams, hence pH is an important factor controlling the mobility of these metals within sediments and their subsequent bioaccumulation within biota. Although sediment-water exchange of Cd can increase with acidification, this excess may be counterbalanced by the presence of ligands in seawater preventing the uptake by organism. Besides chlorines, Cd has also an affinity with carbonates and other ligands present in sea water. These Cd-carbonate complexes may reduce the bioavailable to organisms.

Conclusions

These results highlight the potential implications of sediment acidification, either due to the storage excess of organic matter or to the forced capture of CO₂, on the increasing metal availability to benthic organisms.

Recommendations and perspectives

This kind of studies should be increased to address the influence of acidification in the behavior, bioavailability, toxicity, and risk assessment of contaminants associated with sediments either above sub-seabed geological formations in marine environments or in high enriched by organic matter in estuarine areas. Recently, the capture of CO₂ in marine environments has been approved and started; it is necessary to address the potential impacts associated with leakages or other events occurring during the procedure of injection and storage of CO2.     

Influence of Saharan dust outbreaks and atmospheric stability upon vertical profiles of size-segregated aerosols and water vapor

Vertical profiles of aerosols and meteorological parameters were obtained using a hot air balloon and motorized paraglider. They were studied under anticyclonic conditions in four different contexts. Three flights occurred near sunrise, and one took place in the central hours of the day. The effects of North African dust intrusions were analyzed, whose entrance to the study area took place above the Stable Boundary Layer (SBL) in flight 1 and below it in flight 2. These flights have been compared with a non-intrusion situation (flight 3). A fourth flight characterized the profiles in the central hours of the day with a well-formed Convective Boundary Layer (CBL). With respect to the particle number distribution, the results show that not all sizes increase within the presence of an intrusion; during the first flight the smallest particles were not affected. The particle sizes affected in the second flight fell within the 0.35–2.5 μm interval. Under situations of convective dynamics, the reduction percentage of the particle number concentration reduces with increasing altitude, independently of their size, with respect to stability conditions. The negative vertical gradient for aerosols and water vapor, characteristic of a highly stable SBL (flight 3) becomes a constant profile within a CBL (flight 4). There are two situations that seem to alter the negative vertical gradient of the water vapor mixing ratio within the SBL: the presence of an intrusion and the possible stratification of the SBL based on different degrees of stability.     

Single and combined effects of aluminum (Al<Subscript>2</Subscript>O<Subscript>3</Subscript>) and zinc (ZnO) oxide nanoparticles in a freshwater fish, <Emphasis Type="Italic">Carassius auratus</Emphasis>

The increasing use of nanoparticles (NPs) worldwide has raised some concerns about their impact on the environment. The aim of the study was to assess the toxicity of metal oxide nanoparticles, singly or combined, in a freshwater fish (Carassius auratus). The fish were exposed for 7, 14, and 21 days to different concentrations of NPs (10 μg Al₂O₃.L^?1, 10 μg ZnO.L^?1, 10 μg Al₂O₃.L^?1 plus 10 μg ZnO.L^?1, 100 μg Al₂O₃.L^?1, 100 μg ZnO.L^?1, and 100 μg Al₂O₃.L^?1 plus 100 μg ZnO.L^?1). At the end of each exposure period, antioxidant enzyme activity (catalase, glutathione-S-transferase, and superoxide dismutase), lipid peroxidation, and histopathology were assessed in the gills and livers of C. auratus. The results show an increase in catalase (CAT) and superoxide dismutase (SOD) activity in the gills and livers of fish, especially after 14 days of exposure to single and combined NPs, followed by a reduction at 21 days. An increase in glutathione S-transferase (GST) was observed in gills after 7 days for all tested NP concentrations (single and combined); while in livers, a significant increase was determined after 14 days of exposure to 100 μg.L^?1 of both single ZnO and Al₂O₃ NPs. Lipid peroxidation (LPO) significantly increased in gills after 7 days of exposure to 100 μg.L^?1 Al₂O₃ NPs (single or combined). In livers, LPO increased significantly after 7 days of exposure to all tested concentrations of both single ZnO and Al₂O₃ (except for 10 μg Al₂O₃.L^?1), and after 14 days of exposure to ZnO (10 and 100 μg.L^?1) and Al₂O₃ (100 μg.L^?1)_. The results from histological observations suggest that exposure to metal oxide NPs affected both livers and gills, presenting alterations such as gill hyperplasia and liver degeneration. However, the most pronounced effects were found in gills. In general, this study shows that the tested NPs, single or combined, are capable of causing sub-lethal effects on C. auratus, but when combined, NPs seem to be slightly more toxic than when added alone.     

Emissions Variability Processor (EMVAP): Design,evaluation, and application

Emissions of pollutants such as SO₂ and NOx from external combustion sources can vary widely depending on fuel sulfur content, load, and transient conditions such as startup, shutdown, and maintenance/malfunction. While monitoring will automatically reflect variability from both emissions and meteorological influences, dispersion modeling has been typically conducted with a single constant peak emission rate. To respond to the need to account for emissions variability in addressing probabilistic 1-hr ambient air quality standards for SO₂ and NO₂, we have developed a statistical technique, the Emissions Variability Processor (EMVAP), which can account for emissions variability in dispersion modeling through Monte Carlo sampling from a specified frequency distribution of emission rates. Based upon initial AERMOD modeling of from 1 to 5 years of actual meteorological conditions, EMVAP is used as a postprocessor to AERMOD to simulate hundreds or even thousands of years of concentration predictions. This procedure uses emissions varied hourly with a Monte Carlo sampling process that is based upon the user-specified emissions distribution, from which a probabilistic estimate can be obtained of the controlling concentration. EMVAP can also accommodate an advanced Tier 2 NO₂ modeling technique that uses a varying ambient ratio method approach to determine the fraction of total oxides of nitrogen that are in the form of nitrogen dioxide. For the case of the 1-hr National Ambient Air Quality Standards (NAAQS, established for SO₂ and NO₂), a “critical value” can be defined as the highest hourly emission rate that would be simulated to satisfy the standard using air dispersion models assuming constant emissions throughout the simulation. The critical value can be used as the starting point for a procedure like EMVAP that evaluates the impact of emissions variability and uses this information to determine an appropriate value to use for a longer term (e.g., 30-day) average emission rate that would still provide protection for the NAAQS under consideration. This paper reports on the design of EMVAP and its evaluation on several field databases that demonstrate that EMVAP produces a suitably modest overestimation of design concentrations. We also provide an example of an EMVAP application that involves a case in which a new emission limitation needs to be considered for a hypothetical emission unit that has infrequent higher-than-normal SO₂ emissions.

ImplicationsEmissions of pollutants from combustion sources can vary widely depending on fuel sulfur content, load, and transient conditions such as startup and shutdown. While monitoring will automatically reflect this variability on measured concentrations, dispersion modeling is typically conducted with a single peak emission rate assumed to occur continuously. To realistically account for emissions variability in addressing probabilistic 1-hr ambient air quality standards for SO₂ and NO₂, the authors have developed a statistical technique, the Emissions Variability Processor (EMVAP), which can account for emissions variability in dispersion modeling through Monte Carlo sampling from a specified frequency distribution of emission rates.     

Passive treatment of acid mine drainage with high metal concentrations using dispersed alkaline substrate

Passive treatment systems based on the dissolution of coarse calcite grains are widely used to remediate acid mine drainage (AMD). Unfortunately, they tolerate only low metal concentrations or acidity loads, because they are prone to passivation (loss of reactivity due to coating) and/or clogging (loss of permeability) by precipitates. To overcome these problems, a dispersed alkaline substrate (DAS) composed of a fine-grained alkaline reagent (calcite sand) mixed with a coarse inert matrix (wood chips) was developed. The small grains provide a large reactive surface and dissolve almost completely before the growing layer of precipitates passivates the substrate, whereas the dispersion of nuclei for precipitation on the inert surfaces retards clogging. Chemical and hydraulic performance of DAS was investigated in two laboratory columns fed at different flow rates with natural AMD of pH 2.3 to 3.5 and inflow net acidity 1350 to 2300 mg/L as CaCO(3). The DAS columns removed 900 to 1600 mg/L net acidity, 3 to 4.5 times more than conventional passive treatment systems. Regardless of the flow rate employed, Al, Fe(III), Cu, and Pb were virtually eliminated. Minor Zn, Ni, and Cd were removed at low flow rates. High acidity removal is possible because these metals accumulate intentionally in DAS, and their precipitation promotes further calcite dissolution. During 15 mo, DAS operated without clogging at 120 g acidity/m(2).d, four times the loading rate recommended for conventional passive systems; DAS may therefore be capable of treating AMD at sites where influent chemistry precludes the use of other passive systems.     

A method for measuring the anoxic biodegradability under denitrifying conditions

A test for assessing the anoxic biodegradability of organic compounds under denitrifying conditions is proposed. The method is based on the recovery and quantification of the CO2 produced, which is evidence of complete biodegradation of the test compound (added as the sole carbon source). The tests were carried out in a mineral medium, with nitrate as electron acceptor. Whole lake sediments, sediment extracts and a commercial inoculum were assayed as a possible inoculum source by means of glucose biodegradability tests. It was found that the sediment extracts constitute a suitable and environmentally-relevant inoculum source, since they add non-significant amounts of carbon to the tests. Two xenobiotic compounds, namely, aniline and phenol, were tested in the aforementioned conditions as well as in a standard aerobic biodegradability test. Both aniline and phenol attained a biodegradation level higher than 60% in a short time period (<28 days) and thus can be considered as readily biodegradable in denitrifying environments. Nevertheless, the kinetics obtained in the anoxic test were slower than in aerobic conditions, and even suggested the accumulation of intermediate metabolites in the case of phenol. The results of this study indicate that the fate of xenobiotic compounds under anoxic conditions differs from that observed in an oxic environment, and therefore it should be considered by standard biodegradability testing procedures.