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Arsenic concentrations in a drinking water reservoir system in the Eastern Ore mountains (Osterzgebirge, Germany) were observed over a 17-year period. The region experienced an environmental change during the past 20 years with decreasing acid, sulphur and nitrogen deposition and a recovering vitality of forested catchment sites. An increase of the arsenic content in the reservoir waters during that change was observed. This was caused by a diminished nitrate supply leading to lower redox potential in the sediments favouring sediment arsenic release. The recent annual cycle in the Altenberg reservoir water arsenic concentration was found to be independent from artificial aeration of the hypoxic hypolimnion during the summer stratification. However, we found a strong seasonal dependent change in water As concentration, with a maximum in autumn and a minimum in spring. The low productive system is driven by peat derived organic matter. For the recent arsenic catchment yield coherencies to dissolved organic carbon export and runoff intensity were found, indicating rising arsenic loads due to climate-related soil organic matter destabilization. Thus, in the reservoir system, both dry and wet climate conditions can increase the water As concentrations due to an internal arsenic release and a catchment arsenic import. [ABSTRACT FROM AUTHOR]

The role of in-stream aquatic vegetation as ecosystem engineers in the distribution of organic matter was investigated in the Okavango Delta, one of the world's largest oligotrophic wetlands. The Okavango channel beds are covered up to 50% with submerged macrophyte patches. By accumulating and concentrating organic matter in the sediments below the patches, macrophytes are likely able to locally forestall a deficiency of nutrients. Up to 21 times more N, 18 times more C, 13 times more P and 6 times more Si can be found in vegetated sediments compared to non-vegetated sediments. Nutrient specific accumulation relates to its relative scarcity in the overlaying water. There is a depletion of dissolved N relative to P, whereas Si is relatively abundant. The Okavango Delta water can generally be characterised as oligotrophic based on plant species composition (e.g. presence of carnivorous plants and absence of floating plants), low plant N:P ratios, and low nutrient- and element-concentrations. Local mineralization and intensified nutrient cycling in the sediments is hypothesized to be crucial for the macrophytes' survival because it provides a key source of the essential nutrients which plants otherwise cannot obtain in sufficient quantities from the nutrient poor water. By engineering the ecosystem as such, channel vegetation also retards the loss of elements and nutrients to island groundwater flow, contributing to one of the key processes driving the high productivity of the Okavango Delta, making it unique among its kind. [ABSTRACT FROM AUTHOR]

In recent years the association of conditioned pain modulation (CPM) with trait fear and anxiety has become a hot topic in pain research due to the assumption that such variables may explain the low CPM efficiency in some individuals. However, empirical evidence concerning this association is still equivocal. Our study is the first to investigate the predictive power of fear and anxiety for CPM by using a well-established psycho-physiological measure of trait fear, i.e. startle potentiation, in addition to two self-report measures of pain-related trait anxiety. Forty healthy, pain-free participants (female: N = 20; age: M = 23.62 years) underwent two experimental blocks in counter-balanced order: (1) a startle paradigm with affective picture presentation and (2) a CPM procedure with hot water as conditioning stimulus (CS) and contact heat as test stimulus (TS). At the end of the experimental session, pain catastrophizing (PCS) and pain anxiety (PASS) were assessed. PCS score, PASS score and startle potentiation to threatening pictures were entered as predictors in a linear regression model with CPM magnitude as criterion. We were able to show an inhibitory CPM effect in our sample: pain ratings of the heat stimuli were significantly reduced during hot water immersion. However, CPM was neither predicted by self-report of pain-related anxiety nor by startle potentiation as psycho-physiological measure of trait fear. These results corroborate previous negative findings concerning the association between trait fear/anxiety and CPM efficiency and suggest that shifting the focus from trait to state measures might be promising. [ABSTRACT FROM AUTHOR]

Purpose: The main objective of this study is to enhance our knowledge about the interplay between the plant Si content and the plant nutrient content as well as the nutrient stoichiometry for a broad range of submerged and emergent wetland plants. Methods: We investigated the carbon, nitrogen, phosphorus and silicon content of 16 species (10 submerged and 6 emergent) along a transect within the Biebrza river (Poland) at 10 locations for the years 2006 and 2007. In addition, the relationships between silicon and carbon, nitrogen and phosphorus content as well as the calculated nutrient ratios (C/N, C/P and N/P) were analyzed. Results: We found evidence for a significant relation of Si to major nutrients carbon and nitrogen (negative correlation) and phosphorus (positive correlation) within wetland plants. Our results show that especially submerged plants are able to substitute carbon compounds in a significant share by silicon compounds. Nitrogen however is partially substituted by Si for emergent plants. This change in plant nutrient content in turn alters the nutrient stoichiometry of C : N : P. Conclusion: Our data is the first showing a possible important effect of plant Si content on plant nutrition and nutrient cycling in wetlands. Plant Si has to be considered in plant ecology, physiology and biogeochemistry of wetland plants, because of its effects on the plant nutrient state. Furthermore, Si may also possibly affect the carbon and nutrient turnover via altered plant nutrient content and subsequently via litter decomposition. [ABSTRACT FROM AUTHOR]

Plant diversity is an important driver of nitrogen and phosphorus stocks in aboveground plant biomass of grassland ecosystems, but plant diversity effects on other elements also important for plant growth are less understood. We tested whether plant species richness, functional group richness or the presence/absence of particular plant functional groups influences the Si and Ca concentrations (mmol g) and stocks (mmol m) in aboveground plant biomass in a large grassland biodiversity experiment (Jena Experiment). In the experiment including 60 temperate grassland species, plant diversity was manipulated as sown species richness (1, 2, 4, 8, 16) and richness and identity of plant functional groups (1-4; grasses, small herbs, tall herbs, legumes). We found positive species richness effects on Si as well as Ca stocks that were attributable to increased biomass production. The presence of particular functional groups was the most important factor explaining variation in aboveground Si and Ca stocks (mmol m). Grass presence increased the Si stocks by 140 % and legume presence increased the Ca stock by 230 %. Both the presence of specific plant functional groups and species diversity altered Si and Ca stocks, whereas Si and Ca concentration were affected mostly by the presence of specific plant functional groups. However, we found a negative effect of species diversity on Si and Ca accumulation, by calculating the deviation between mixtures and mixture biomass proportions, but in monoculture concentrations. These changes may in turn affect ecosystem processes such as plant litter decomposition and nutrient cycling in grasslands. [ABSTRACT FROM AUTHOR]