Abstract

Formation of the greenhouse gas nitrous oxide in water treatment systems is predominantly studied as a biological phenomenon. There are indications that also chemical processes contribute to these emissions. Here we studied the formation of nitric oxide (NO) and nitrous oxide (N(2)O) due to chemical nitrite reduction by ferrous iron (Fe(II)). Reduction of nitrite and NO coupled to Fe(II) oxidation was studied in laboratory-scale chemical experiments at different pH, nitrite and iron concentrations. The continuous measurement of both NO and N(2)O emission showed that nitrite reduction and NO reduction have different kinetics. Nitrite reduction shows a linear dependency on the nitrite concentration, implying first order kinetics in nitrite. The nitrite reduction seems to be an equilibrium based reaction, leading to a constant NO concentration in the liquid. The NO reduction rate is suggested to be most dependent on reactive surface availability and the sorption of Fe(II) to the reactive surface. The importance of emission of NO and N(2)O coupled to iron oxidation is exemplified by iron reduction experiments and several examples of environments where this pathway can play a role. More >>

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Abstract

In this paper, we introduce an ecologically relevant measure of drought stress and its relationship with vegetation characteristics. We used process-based simulations of reference drought stress on inclined surfaces with different soil type, slope, and aspect to get an insight in the drought statistics that explain small-scale differences in vegetation characteristics. Mean intensity, duration, and frequency of drought events are commonly integrated into the so-called “dynamic drought stress” TSdyn. We introduce a simple, physiology-based alternative measure of drought stress TSupp, based on the finding that plants respond to extremes rather than to mean intensities of stress events. Using extremes instead of mean intensities makes information on duration and frequency of stress events superfluous. We show that compared with TSdyn, TSupp (i) is a better predictor of the fraction of xerophytes within a vegetation plot, (ii) is simple, transparent, and easy to interpret as only the uppermost intensities are involved, i.e. minimum parameters are needed, and (iii) does not involve empirical parameters, as are used in TSdyn. Focusing on extremes rather than on means is especially important in predicting climate change effects, as especially these extremes are predicted to increase due to climate change. More >>

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Abstract

Robust relationships among soil, water, atmosphere and plants are needed to reliably forecast the plant species composition. In this paper, we show the need for, and the application of, a process-based relationship between soil moisture conditions and vegetation characteristics. We considered 366 groundwater-dependent sites, where oxygen stress, caused by a surplus of soil moisture, codetermines plant performance. We compared two existing indirect proxies for the soil oxygen status – namely mean spring groundwater level (MSL) and sum exceedence value (SEV) – with our newly developed process-based proxy, viz. root respiration stress (RS). The two indirect proxies and the process-based proxy for oxygen stress performed equally well in describing vegetation characteristics for the Netherlands under the current climate. However, relationships based on MSL and SEV appeared to produce systematic prediction errors when applied outside their calibration range, in contrast to the relationship based on RS. Hence, the two indirect proxies cannot be used in projections, such as in predicting effects of climate change on vegetation composition, all the more because they – unlike RS – do not account for essential parameters that determine oxygen stress (e.g. temperature and extreme rainfall events in the growing season). We advocate using RS for estimating vegetation impacts in climate projections to increase the reliability and effectiveness of adaptive strategies. More >>

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Abstract

There is a growing evidence base demonstrating that atmospheric nitrogen deposition presents a threat to biodiversity and ecosystem function in acid grasslands in Western Europe. Here, we report the findings of a workshop held for European policy makers to assess the perceived importance of reactive nitrogen deposition for grassland conservation, identify areas for policy development in Europe and assess the potential for managing and mitigating the impacts of nitrogen deposition. The importance of nitrogen as a pollutant is already recognized in European legislation, but there is little emphasis in policy on the evaluation of changes in biodiversity due to nitrogen. We assess the potential value of using typical species, as defined in the European Union Habitats Directive, for determining the impact of nitrogen deposition on acid grasslands. Although some species could potentially be used as indicators of nitrogen deposition, many of the typical species do not respond strongly to nitrogen deposition and are unlikely to be useful for identifying impact on an individual site. We also discuss potential mitigation measures and novel ways in which emissions from agriculture could be reduced. More >>

You will find more peer reviewed articles on 'KWR Publications'