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Aline Schäfer Rodrigues Silva Markus Noack Dirk Schlabing Silke Wieprecht 《Journal of Soils and Sediments》2018,18(10):3070-3081
Purpose
The critical shear stress of cohesive and mixed cohesive/non-cohesive sediments is affected by multiple interacting physical, chemical and biological parameters. There are various mathematical approaches in the scientific literature for computing critical shear stress. However, processes that influence sediment stability are still not fully understood, and available formulas differ considerably. These discrepancies in the literature arise from random system behaviour (natural variability of the sediments), different definitions of the critical shear stress, different measurement techniques and different model frameworks (scope of the parameters, undisturbed versus artificial sediment samples). While analytical approaches fail to address the involved uncertainties, fuzzy logic-based models integrate uncertainty and imprecision.Materials and methods
With this in mind, a data-driven neuro-fuzzy model (ANFIS) was used to determine the critical shear stress based on sediment characteristics such as wet bulk density and grain size distribution. In order to select model predictors systematically, an automated stepwise regression algorithm was applied. The database for this analysis consisted of 447 measurements of the critical shear stress originating from 64 undisturbed sediment samples.Results and discussion
The study identified clay content as the primarily controlling variable for erosion resistance. Depending on the characteristics of the sampling location, the bulk density was also selected as a model predictor. In comparison to analytical models that are available in the scientific literature, the fuzzy model achieved higher correlation coefficients between measured and predicted data.Conclusions
The neuro-fuzzy-model includes uncertainties of input variables and their interactions directly. Thus, it provides a reliable method for the prediction of erosion thresholds of cohesive/non-cohesive mixtures. It was also shown that this approach requires fewer measured variables as well as fewer assumptions than the models it was compared to.3.
We present results from the Brocken Cloud Chemistry Measurement Project (BROCCMON) which started in 1991. Since 1992 the full programme is running, based on continuous measurements (e.g. trace gases, meteorology, liquid water content), cloud water sampling and analysis and intensive measurement campaigns. The observed high variability of cloud water composition we explain with cloud dynamic and microphysical behaviour of clouds and differences in the air mass characteristics. During the measurement period 1992–1994 we observed an increase in cloud water acidity (by a factor of 3) and we found photochemical conditions typically for summersmog situations. Our preliminary data also show that an understanding of tropospheric ozone balance would be incomplete without consideration of chemical processes within clouds. A long-term goal of our programme is to establish a cloud chemistry climatology which is representative for the region. 相似文献
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B. C. Oinam W. Marx T. Scholten S. Wieprecht 《Land Degradation \u0026amp; Development》2014,25(5):483-500
Land use practices and vegetation cover distribution are considered to be the most important dynamic factors that influence the land degradation or the soil erosion of a region. In this study, a Soil Protection Index (SPI) is defined as a function of land use practices and intensity of vegetation cover. This index is used to map the relative degree of protection of topsoil from being eroded by external effects such as rainfall and overland flow. A fuzzy rule‐based model integrated within ArcGIS® has been set‐up and tested with the aim to develop SPI maps. The amount of vegetation cover distribution, that is, Normalized Difference Vegetation Index as proxy parameter and Land Use–Land Cover map are chosen as fuzzy input parameters for the SPI as the desired system output. The approach was tested in the Upper Awash basin in Ethiopia. The output SPI map was qualitatively evaluated against the expert‐defined land degradation risk class, and it was found that locations that are mapped with ‘low and very low’ SPI classes at different time periods of the year have a high potential land degradation risk. Furthermore, socio‐economic data (‘population and livestock densities’) and environmental parameters (‘altitude and soil erodibility’) for the region are used to correlate with the SPI map as an indirect method of evaluation. It is found that population and livestock density explained 68 per cent of the spatial distribution pattern of predicted SPI and an adjusted R‐squared value of 0·681 (p < 0·05) was obtained. It was also found that the SPI distribution over the region for two different time periods, that is, January and July 2001, correlated positively (R2 = 0·41 and R2 = 0·51) with the soil erodibility of the region. The transferability and applicability of the model for different environmental settings or landscapes were tested by mapping the SPI of Italy. This SPI map of Italy was compared with the soil erosion map of Italy produced by the European Soil Bureau. It can be concluded that the SPI map reflects the potential land degradation risk distribution of the case‐study region. Results show that a fuzzy rule‐based model can provide useful preliminary information even without detailed and precise data information for developing appropriate strategies for land degradation assessment vital for sustainable land use management. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
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Anthropogenic pollutants affect ecosystem services of freshwater sediments: the need for a “triad plus x” approach 总被引：1，自引：0，他引：1
Gerbersdorf Sabine Ulrike Hollert Henner Brinkmann Markus Wieprecht Silke Schüttrumpf Holger Manz Werner 《Journal of Soils and Sediments》2011,11(6):1099-1114
Purpose
Freshwater sediments and their attached microbial communities (biofilms) are essential features of rivers and lakes, providing valuable ecosystem services such as nutrient recycling or self-purification which extend beyond the aquatic environment. Anthropogenic pollutants, whether from the industrial era or as a result of our contemporary lifestyles, can negatively affect these functions with hitherto unknown consequences on ecology, the economy and human health. Thus far, the singular view of the involved disciplines such as ecotoxicology, environmental microbiology, hydrology and geomorphology has prevented a deeper understanding of this emerging issue. 相似文献6.
Acker K. Möller D. Wieprecht W. Auel R. Kalass D. Tscherwenka W. 《Water, air, and soil pollution》2001,130(1-4):331-336
A measurement method for the continuous and in situ analysis of atmospheric concentration of HNO2 and HNO3 inside and outside of clouds has successfully been established. The approach for a wet effluent diffusion denuder (parallel plate design) was adopted and performed quasi on-line with an ion chromatography unit. The air flow through the denuder was 10 1/min and at 15 minutes of preconcentration we are able to record atmospheric concentrations of 15 ng/m3 of HNO2 and HNO3, respectively. Field measurements using the denuder system were done at the Mt. Brocken summit (1142 m a.s.l., Harz Mountains, Germany) in 1998 and 1999. During day-time and under clear conditions maximum values of HNO3 up to 7000 ng/m3 were observed. Measurements performed during cloud events assess first time our expectation that the comparatively very great specific droplet surface in clouds is a place for a heterogeneous HNO2 formation, after nocturnal accumulation up to 320 ng/m3 were found. Strong positive correlation between HNO2 concentrations and those of NO2 were obtained during and after cloud events to assess the origin of the observed nitrous acid. The HNO2/NO2 ratio reached 10% under humid conditions. The observed surface to volume ratios in investigated clouds were between 0.4 and 0.7. In dependence on the cloud water pH nitrite concentrations between 5–300 µg/l (1–30 ng/m3 air) were observed. 相似文献
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