Indices of biotic integrity have become an established tool to quantify the condition of small non-tidal streams and their
watersheds. To investigate the effects of watershed characteristics on stream biological condition, we present a new technique
for regressing IBIs on watershed-specific explanatory variables. Since IBIs are typically evaluated on an ordinal scale, our
method is based on the proportional odds model for ordinal outcomes. To avoid overfitting, we do not use classical maximum
likelihood estimation but a component-wise functional gradient boosting approach. Because component-wise gradient boosting
has an intrinsic mechanism for variable selection and model choice, determinants of biotic integrity can be identified. In
addition, the method offers a relatively simple way to account for spatial correlation in ecological data. An analysis of
the Maryland Biological Streams Survey shows that nonlinear effects of predictor variables on stream condition can be quantified
while, in addition, accurate predictions of biological condition at unsurveyed locations are obtained. 相似文献
Accumulations of iron, manganese, and arsenic occur in the Chandina alluvium of southeastern Bangladesh within 2.5 m of the
ground surface. These distinctive orange-brown horizons are subhorizontal and consistently occur within 1 m of the contact
of the aerated (yellow-brown) and water-saturated (gray) sediment. Ferric oxyhydroxide precipitates that define the horizons
form by oxidation of reduced iron in pore waters near the top of the saturated zone when exposed to air in the unsaturated
sediment. Hydrous Fe-oxide has a high specific surface area and thus a high adsorption capacity that absorbs the bulk of arsenic
also present in the reduced pore water, resulting in accumulations containing as much as 280 ppm arsenic. The steep redox
gradient that characterizes the transition of saturated and unsaturated sediment also favors accumulation of manganese oxides
in the oxidized sediment. Anomalous concentrations of phosphate and molybdenum also detected in the ferric oxyhydroxide-enriched
sediment are attributed to sorption processes. 相似文献
Although the terrestrial carbon budget is of key importance for atmospheric CO2 concentrations, little is known on the effects of management and natural disturbances on historical carbon stocks at the
regional scale. We reconstruct the dynamics of vegetation carbon stocks and flows in forests across the past 100 years for
a valley in the eastern Swiss Prealps using quantitative and qualitative information from forest management plans. The excellent
quality of the historical information makes it possible to link dynamics in growing stocks with high-resolution time series
for natural and anthropogenic disturbances. The results of the historical reconstruction are compared with modelled potential
natural vegetation. Forest carbon stock at the beginning of the twentieth century was substantially reduced compared to natural
conditions as a result of large scale clearcutting lasting until the late nineteenth century. Recovery of the forests from
this unsustainable exploitation and systematic forest management were the main drivers of a strong carbon accumulation during
almost the entire twentieth century. In the 1990s two major storm events and subsequent bark beetle infestations significantly
reduced stocks back to the levels of the mid-twentieth century. The future potential for further carbon accumulation was found
to be strongly limited, as the potential for further forest expansion in this valley is low and forest properties seem to
approach equilibrium with the natural disturbance regime. We conclude that consistent long-term observations of carbon stocks
and their changes provide rich information on the historical range of variability of forest ecosystems. Such historical information
improves our ability to assess future changes in carbon stocks. Further, the information is vital for better parameterization
and initialization of dynamic regional scale vegetation models and it provides important background for appropriate management
decisions. 相似文献
In order to make projections for future air-quality levels, a robust methodology is needed that succeeds in reconstructing present-day air-quality levels. At present, climate projections for meteorological variables are available from Atmospheric-Ocean Coupled Global Climate Models (AOGCMs) but the temporal and spatial resolution is insufficient for air-quality assessment. Therefore, a variety of methods are tested in this paper in their ability to hindcast maximum 8 hourly levels of O3 and daily mean PM10 from observed meteorological data. The methods are based on a multiple linear regression technique combined with the automated Lamb weather classification. Moreover, we studied whether the above-mentioned multiple regression analysis still holds when driven by operational ECMWF (European Center for Medium-Range Weather Forecast) meteorological data. The main results show that a weather type classification prior to the regression analysis is superior to a simple linear regression approach. In contrast to PM10 downscaling, seasonal characteristics should be taken into account during the downscaling of O3 time series. Apart from a lower explained variance due to intrinsic limitations of the regression approach itself, a lower variability of the meteorological predictors (resolution effect) and model deficiencies, this synoptic-regression-based tool is generally able to reproduce the relevant statistical properties of the observed O3 distributions important in terms of European air quality Directives and air quality mitigation strategies. For PM10, the situation is different as the approach using only meteorology data was found to be insufficient to explain the observed PM10 variability using the meteorological variables considered in this study. 相似文献
The evaluation of radioactivity accidentally released into the atmosphere involves determining the radioactivity levels of rainwater samples. Rainwater scavenges atmospheric airborne radioactivity in such a way that surface contamination can be deduced from rainfall rate and rainwater radioactivity content. For this purpose, rainwater is usually collected in large surface collectors and then measured by γ-spectrometry after such treatments as evaporation or iron hydroxide precipitation. We found that collectors can be adapted to accept large surface (diameter 47 mm) cartridges containing a strongly acidic resin (Dowex AG 88) which is able to quantitatively extract radioactivity from rainwater, even during heavy rainfall. The resin can then be measured by γ-spectrometry. The detection limit is 0.1 Bq per sample of resin (80 g) for 137Cs. Natural 7Be and 210Pb can also be measured and the activity ratio of both radionuclides is comparable with those obtained through iron hydroxide precipitation and air filter measurements. Occasionally 22Na has also been measured above the detection limit. A comparison between the evaporation method and the resin method demonstrated that 2/3 of 7Be can be lost during the evaporation process. The resin method is simple and highly efficient at extracting radioactivity. Because of these great advantages, we anticipate it could replace former rainwater determination methods. Moreover, it does not necessitate the transportation of large rainwater volumes to the laboratory. 相似文献
The impact of UV-B radiation on 10 genotypically different barley and tomato cultivars was tested in a predictive study to screen for potentially UV-tolerant accessions and to analyze underlying mechanisms for UV-B sensitivity. Plant response was analyzed by measuring thermoluminescence, fluorescence, gas exchange and antioxidant status. Generally, barley cultivars proved to be much more sensitive against UV-B radiation than tomato cultivars. Statistical cluster analysis could resolve two barley groups with distinct differences in reaction patterns. The UV-B sensitive group showed a stronger loss in PSII photochemistry and a lower gas-exchange performance and regulation after UV-B radiation compared to the more tolerant group. The results indicate that photosynthetic light and dark reactions have to play optimally in concert to render plants more tolerant against UV-B radiation. Hence, measuring thermoluminescence/fluorescence and gas exchange in parallel will have much higher potential in identifying tolerant cultivars and will help to understand the underlying mechanisms. 相似文献
Medical isotope production facilities (MIPF) have recently been identified to emit the major part of the environmental radioxenon measured at many globally distributed monitoring sites deployed to strengthen the radionuclide component of the Comprehensive Nuclear-Test-Ban Treaty (CTBT) verification regime. Efforts to raise a global radioxenon emission inventory revealed that the yearly global total emission from MIPF’s is around 15 times higher than the total radioxenon emission from nuclear power plants (NPP's).Given that situation, from mid 2008 until early 2009 two out of the ordinary hemisphere-specific events occured:1) In the Northern hemisphere, a joint temporary suspension of operations of the three largest MIPF's made it possible to quantify the effects of the emissions related to NPP’s. The average activity concentrations of 133Xe measured at a monitoring station close to Freiburg, Germany, went down significantly from 4.5 ± 0.5 mBq/m3 to 1.1 ± 0.1 mBq/m3 and in Stockholm, Sweden, from 2.0 ± 0.4 mBq/m3 to 1.05 ± 0.15 mBq/m3.2) In the Southern hemisphere the only radioxenon-emitting MIPF in Australia started up test production in late November 2008. During eight test runs, up to 6.2 ± 0.2 mBq/m3 of 133Xe was measured at the station in Melbourne, 700 km south-west from the facility, where no radioxenon had been observed before, originating from the isotopic production process.This paper clearly confirms the hypothesis that medical isotope production facility are at present the major emitters of radioxenon to the atmosphere. Suspension of operations of these facilities indicates the scale of their normal contribution to the European radioxenon background, which decreased two to four fold. This also gives a unique opportunity to detect and investigate the influence of other local and long distance sources on the radioxenon background. Finally the opposing effect was studied: the contribution of the start-up of a renewed radiopharmaceutical facility to the build up of a radioxenon background across Australia and the Southern hemisphere. 相似文献
While toxicological data are available for numerous chemicals from standard tests, little is known on effects of pollutants over several generations or regarding chronic effects of chemicals on genetic diversity. Within the experiments, effects of the model pollutant tributyltin (TBT) were investigated over eleven generations at a sublethal TBT concentration of 4.46 μg as Sn kg−1 sediment dw on life-cycle parameters and genetic variability of Chironomus riparius. Moreover, the adaptation potential towards TBT was determined. This experimental design enables the identification of TBT effects on life-cycle parameters and the determination of a potential extinction risk caused by chronic exposure. Furthermore, effects on the genetic structure can be determined, which are not predictable based solely on knowledge of the toxic mode of action of the chemical.
Genetic variety was determined via microsatellite analysis, measuring individual length differences of highly variable satellite DNA fragments. For the identification of changes in tolerances towards the stressor, acute and chronic toxicity experiments were conducted.
During the multi-generation study, significant effects on development and reproduction were determined. For some generations, the emergence was significantly (p < 0.05) delayed under TBT exposure. Reproduction seems to be a sensitive parameter as well, whereby females laid significantly larger egg masses (p < 0.05) in the latter generations. TBT did not affect the population growth rate nor the genetic variability, while clear deviations from the Hardy–Weinberg equilibrium appeared. The study also provides strong evidence for the acquirement of a higher tolerance towards the stressor in the TBT-exposed group. 相似文献
Lab-scale experiments were conducted to assess the impact of thermobarical treatment of cattle waste on anaerobic digestion. Treatment was at temperatures of 140–220 °C in 20 K steps for a 5-min duration. Methane yields could be increased by up to 58% at a treatment temperature of 180 °C. At 220 °C the abundance of inhibitors and other non-digestible substances led to lower methane yields than those obtained from untreated material. In an extended analysis it could be demonstrated that there is a functional correlation between the methane yields after 30 days and the formation rate and methane yield in the acceleration phase. It could be proved in a regression of these correlation values that the optimum treatment temperature is 164 °C and that the minimum treatment temperature should be above 115 °C. 相似文献
To better understand the potential for successful and long-term establishment of environmental policy, the aim of this paper is to explore the network dynamics of a policy field that has become well established in the EU: organic farming. We look at the dynamics of the organic farming policy network in the Czech Republic over a period of 10 years by applying a comparative formal network analysis. We focused in particular on the distribution of power between actors and how capacities of policy actors have evolved between 2004 (its year of accession to the EU) and 2014. We conclude that the organic farming policy network in the Czech Republic has been highly dynamic and has changed from one that was decidedly influenced by organic sector organizations to a network centralized around the Ministry of Agriculture. However, the organic farming organization managed to maintain its good reputation for competence in organic farming policy, which creates opportunities for the organization to remain active in the policy debate. 相似文献