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271.
Steven D. Warren Victor E. Diersing Pamela J. Thompson William D. Goran 《Environmental management》1989,13(2):251-257
The universal soil loss equation (USLE) has been integrated with a geographic information system known as the geographical resources analysis support system (GRASS) to create a land classification system for use by military trainers and land managers to minimize the environmental impacts of military training activities. The USLE provides an estimate of current average annual sheet and rill erosion based upon factors representing climate, soil erodibility, topography, cover, and conservation support practices. The erosion estimate is compared to erosion tolerance values to produce an expression of the current erosion status. An index of inherent site erodibility is also achieved through manipulation of the USLE. Based on published soil surveys, satellite imagery, and ground-truth vegetation transects, data layers are created within GRASS for each of the component factors of the USLE. Appropriate mathematical operations are performed with the data layers, and color-coded maps are produced that represent the erosion status and erodibility index for each 50-m × 50-m area of soil surface. These maps aid military trainers and land managers in scheduling appropriate kinds and intensities of military training activities. 相似文献
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Turnover rates of soil carbon for 20 soil types typical for a 3.7 million km2 area of European Russia were estimated based on 14C data. The rates are corrected for bomb radiocarbon which strongly affects the topsoil 14C balance. The approach is applied for carbon stored in the organic and mineral layers of the upper 1 m of the soil profile. The turnover rates of carbon in the upper 20 cm are relatively high for forest soils (0.16–0.78% year−1), intermediate for tundra soils (0.25% year−1), and low for grassland soils (0.02–0.08% year−1) with the exception of southern Chernozems (0.32% year−1). In the soil layer of 20–100 cm depth, the turnover rates were much lower for all soil types (0.01–0.06% year−1) except for peat bog soils of the southern taiga (0.14% year−1). Combined with a map of soil type distribution and a dataset of several hundred soil carbon profiles, the method provides annual fluxes for the slowest components of soil carbon assuming that the latter is in equilibrium with climate and vegetation cover. The estimated carbon flux from the soil is highest for forest soils (12–147 gC/(m2 year)), intermediate for tundra soils (33 gC/(m2 year)), and lowest for grassland soils (1–26 gC/(m2 year)). The approach does not distinguish active and recalcitrant carbon fractions and this explains the low turnover rates in the top layer. Since changes in soil types will follow changes in climate and land cover, we suggest that pedogenesis is an important factor influencing the future dynamics of soil carbon fluxes. Up to now, both the effect of soil type changes and the clear evidence from 14C measurements that most soil organic carbon has a millennial time scale, are basically neglected in the global carbon cycle models used for projections of atmospheric CO2 in 21st century and beyond. 相似文献
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Vyverman W Verleyen E Sabbe K Vanhoutte K Sterken M Hodgson DA Mann DG Juggins S Van de Vijver B Jones V Flower R Roberts D Chepurnov VA Kilroy C Vanormelingen P De Wever A 《Ecology》2007,88(8):1924-1931
There is a long-standing belief that microbial organisms have unlimited dispersal capabilities, are therefore ubiquitous, and show weak or absent latitudinal diversity gradients. In contrast, using a global freshwater diatom data set, we show that latitudinal gradients in local and regional genus richness are present and highly asymmetric between both hemispheres. Patterns in regional richness are explained by the degree of isolation of lake districts, while the number of locally coexisting diatom genera is highly constrained by the size of the regional diatom pool, habitat availability, and the connectivity between habitats within lake districts. At regional to global scales, historical factors explain significantly more of the observed geographic patterns in genus richness than do contemporary environmental conditions. Together, these results stress the importance of dispersal and migration in structuring diatom communities at regional to global scales. Our results are consistent with predictions from the theory of island biogeography and metacommunity concepts and likely underlie the strong provinciality and endemism observed in the relatively isolated diatom floras in the Southern Hemisphere. 相似文献
279.
Griet Casteleyn Katharine M. Evans Thierry Backeljau Sofie D’hondt Victor A. Chepurnov Koen Sabbe Wim Vyverman 《Marine Biology》2009,156(6):1149-1158
Several marine holoplanktonic organisms show a high degree of geographically structured diversity for which it often remains
unclear to what extent this differentiation is due to the presence of cryptic taxa. For the genetically distinct diatom Pseudo-nitzschia pungens var. pungens, we used six microsatellite markers to investigate the spatial and temporal genetic composition in the heterogeneous Southern
Bight of the North Sea. Although our sampling area (ca. 100 km) comprised water bodies with different environmental conditions
(marine, estuary, saline lake) and different degrees of connectivity (from complete isolation to supposedly free exchange
between environments), no evidence of genetic differentiation was found. Expanding our sampling area (ca. 650 km), suggested
a homogenous population structure over even larger areas in the North Sea. Our results suggest that the population structure
of this diatom is mainly shaped by strong homogenizing effects of gene flow preventing genetic drift, even in water bodies
with limited connectivity.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
280.
Nitroglycerine (NG) and 2,4-dinitrotoluene (2,4-DNT) are propellants often found in soil and groundwater at military firing ranges. Because of the need for training with live ammunition, control or cleanup of these contaminants may be necessary for the continued use of these firing ranges. One inexpensive approach for managing sites exposed to these contaminants is the use phytoremedation, particularly using common or native grasses. In this study, the uptake of NG and 2,4-DNT from water by three common grasses, yellow nutsedge (Cyperus escalantus), yellow foxtail (Setaria glauca), and common rush (Juncus effusus), was investigated using hydroponic reactors. Rapid removal from solution by all grasses was observed, with yellow nutsedge removal rates being the highest. NG or 2,4-DNT accumulated in the tissues in all of the plants, except yellow foxtail did not accumulate NG. Higher concentrations were observed in killed roots, demonstrating the presence of plant-based enzymes actively transforming the contaminants. Yellow nutsedge was also grown in 2,4-DNT spiked soil. Significant uptake into the plants roots and leaves was observed and concentrations in the soil decreased rapidly, although 2,4-DNT concentration also decreased in the unplanted controls. In summary, the three grasses tested appear to be good candidates for phytoremediation of propellant contamination. 相似文献