Taxonomic and functional macroinvertebrate diversity of high-altitude ponds in the Macun Cirque,Switzerland

1. Global environmental change is threatening freshwater biodiversity with ecological impacts predicted to be particularly severe in high-altitude regions. Despite this, an ecological understanding of high-altitude pond networks remains patchy, with only limited knowledge of the environmental and spatial predictors of taxonomic and functional diversity. Moreover, previous studies of pond ecosystems have focused primarily on taxonomic richness and largely overlooked functional diversity.
2. This study examined the influence of local environmental and spatial factors on taxonomic and functional α and β diversity (including the turnover and nestedness-resultant components) of 17 high-altitude (~2,500 m above sea level) pond macroinvertebrate communities, in the Macun Cirque, Switzerland.
3. Spatial processes (pond connectivity) were important drivers for taxonomic α diversity, while local environmental variables (pond permanence and surface area) were important determinants of functional α diversity. Species turnover was the most important component of β diversity for taxonomic composition, and functional composition demonstrated a nested spatial pattern.
4. Variation in taxonomic and functional composition (and the turnover and nestedness components of β diversity) were determined by local environmental variables despite the limited environmental gradients within the pond network. No significant effects of spatial variables on community composition were recorded for either facet of diversity, indicating that compositional variation was determined at a local scale. Water temperature, depth and pond permanence were consistently the most important measured drivers of diversity.
5. Given the importance of both spatial and environmental variables in structuring taxonomic and functional diversity, landscape-scale conservation and management activities that aim to improve or protect high-altitude freshwater biodiversity should focus on maintaining connectivity among ponds and environmental heterogeneity, particularly pond surface area, water depth, and hydroperiod. Understanding the mechanisms driving taxonomic and functional diversity will be critically important for the management and conservation of macroinvertebrate communities in high-altitude pond networks in the face of climatic warming.

     

Is the decline of soil microbial biomass in late winter coupled to changes in the physical state of cold soils?

During winter when the active layer of Arctic and alpine soils is below 0 °C, soil microbes are alive but metabolizing slowly, presumably in contact with unfrozen water. This unfrozen water is at the same negative chemical potential as the ice. While both the hydrostatic and the osmotic components of the chemical potential will contribute to this negative value, we argue that the osmotic component (osmotic potential) is the significant contributor. Hence, the soil microorganisms need to be at least halotolerant and psychrotolerant to survive in seasonally frozen soils. The low osmotic potential of unfrozen soil water will lead to the withdrawal of cell water, unless balanced by accumulation of compatible solutes. Many microbes appear to survive this dehydration, since microbial biomass in some situations is high, and rising, in winter. In late winter however, before the soil temperature rises above zero, there can be a considerable decline in soil microbial biomass due to the loss of compatible solutes from viable cells or to cell rupture. This decline may be caused by changes in the physical state of the system, specifically by sudden fluxes of melt water down channels in frozen soil, rapidly raising the chemical potential. The dehydrated cells may be unable to accommodate a rapid rise in osmotic potential so that cell membranes rupture and cells lyse. The exhaustion of soluble substrates released from senescing plant and microbial tissues in autumn and winter may also limit microbial growth, while in addition the rising temperatures may terminate a winter bloom of psychrophiles.Climate change is predicted to cause a decline in plant production in these northern soils, due to summer drought and to an increase in freeze-thaw cycles. Both of these may be expected to reduce soil microbial biomass in late winter. After lysis of microbial cells this biomass provides nutrients for plant growth in early spring. These feedbacks, in turn, could affect herbivory and production at higher trophic levels.     

A Modeling Study of the Impact of a Power Plant on Ground-Level Ozone in Relation to its Location: Southwestern Spain as a Case Study

The impact of atmospheric industrial emissions on secondary pollutant formation depends on many factors; one of the most important being the environmental setting in which the industry is located. The environmental setting affects an industry’s impact on ozone levels through both the air mass dispersion (a function of topography and wind patterns) and the emissions of organic volatile compounds (VOC) and nitrogen oxides (NO _x ) in the area. This model-based study shows how the sensitivity of surface ozone changes with the choice of source location. For the analysis, seven points distributed along the Tinto–Guadalquivir Basin (in the Southwestern Iberian Peninsula) were selected. This area is characterized by the close proximity of natural environments and crop fields to cities, roads, and industrial areas with high NO _x emissions. Natural VOC emissions represent more than 60% of the total non-methane volatile organic compounds emitted in the study area. The results reveal that the largest increases in ozone levels are produced when the industry is located both far away from NO _x emission sources and near to biogenic VOC emissions. Furthermore, the highest increases over the hourly and 8-hourly maximums, as well as the highest accumulated daily values, are found in areas characterized by high VOC/NO _x emission ratios and NO _x sensitivity. The study of the recurrent meteorological patterns along with the distribution of chemical indicators of the O₃–NO _x –VOC sensitivity allows the determination of the industry’s geographical impact on ozone levels. This information enables air quality managers to decide the future location of an industry minimizing its impact on smog levels.     

Indications, management, and outcome of long-term positive-pressure ventilation in dogs and cats: 148 cases (1990-2001)

OBJECTIVE: To determine outcome of positive-pressure ventilation (PPV) for 24 hours or longer and identify factors associated with successful weaning from PPV and survival to hospital discharge in dogs and cats. DESIGN: Retrospective case series. ANIMALS: 124 dogs and 24 cats that received PPV for 24 hours or longer. PROCEDURES: Medical records were reviewed for signalment, primary diagnosis, reason for initiating PPV, measures of oxygenation and ventilation before and during PPV, ventilator settings, complications, duration of PPV, and outcome. Animals were categorized into 1 of 3 groups on the basis of the reason for PPV. RESULTS: Group 1 patients received PPV for inadequate oxygenation (67 dogs and 6 cats), group 2 for inadequate ventilation (46 dogs and 16 cats), and group 3 for inadequate oxygenation and ventilation (11 dogs and 2 cats). Of the group 1 animals, 36% (26/73) were weaned from PPV and 22% (16/73) survived to hospital discharge. In group 2, 50% (31/62) were weaned from PPV and 39% (24/62) survived to hospital discharge. In group 3, 3 of 13 were weaned from PPV and 1 of 13 survived to hospital discharge. Likelihood of successful weaning and survival to hospital discharge were significantly higher for group 2 animals, and cats had a significantly lower likelihood of successful weaning from PPV, compared with dogs. Median duration of PPV was 48 hours (range, 24 to 356 hours) and was not associated with outcome. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggested that long-term PPV is practical and successful in dogs and cats.     

Cation exchange capacity of density fractions from paired conifer/grassland soils

The cation exchange capacity (CEC) of a soil depends on the type and amount of both mineral and organic surfaces. Previous studies that have sought to determine the relative contribution of organic matter to total soil CEC have not addressed differences in soil organic matter (SOM) composition that could lead to differences in CEC. The objectives of this study were (1) to compare the CEC of two distinct SOM pools, the “light fraction (LF)” composed of particulate plant, animal, and microbial debris, and the “heavy fraction (HF)” composed of mineral-bound organic matter; and (2) to examine the effects of differences in aboveground vegetation on CEC. Soil samples were collected from four paired grassland/conifer sites within a single forested area and density fractionated. LF CEC was higher in conifer soils than in grassland soils, but there was no evidence of an effect of vegetation on CEC for the HF or bulk soil. LF CEC (but not HF CEC) correlated well with the C concentration in the fraction. The mean CEC of both fractions (per kg fraction) exceeded that of the bulk soil; thus, when the LF and HF CEC were combined mathematically by weighting values for each fraction in proportion to dry mass, the resulting value was nearly twice the measured CEC of bulk soil. On a whole soil basis, the HF contributed on average 97% of the CEC of the whole soil, although this conclusion must be tempered given the inflation of CEC values by the density fractionation procedure.     

Effects of human activity on the foraging behavior of sanderlings Calidris alba

Urbanization and coastal development has dramatically reduced the beach habitat available for foraging shorebirds worldwide. This study tested the general hypothesis that recreational use of shorebird foraging areas adversely affects the foraging behavior of sanderlings Calidris alba. Observations conducted on two central California beaches from January through May and September through December of 1999 showed that number and activity of people significantly reduced the amount of time sanderlings spent foraging. Although the sample size was low, the most significant negative factor was the presence of free running dogs on the beach. The experimentally determined minimal approach distance did not vary significantly with the type of human activities tested. Based on these results, policy recommendations for minimizing the impact of human beach activities on foraging shorebirds include: (1) people maintain a minimum distance of 30 m from areas where shorebirds concentrate and (2) strict enforcement of leash laws.