A number of very serious drough disasters occurred in many regions of Aftica during past 30 years. It is commonly considered that they are among the most serious disasters after the World War II. The basic situation o...A number of very serious drough disasters occurred in many regions of Aftica during past 30 years. It is commonly considered that they are among the most serious disasters after the World War II. The basic situation of the droughs and drough disasters are introduced briefly, and the main causes resulting 1i drought disasters are analysed in the paper. The lack of rainfall is one of the factors producing the drough disasters in Africa, but it is not the real one. From environmental viewpoints, the drough disasters in Africa resulted from unsuitable land use and management by man, and in essence they are the results of man-made environmental disturbance. Finally, the strategy for preventing drought disasters in Africa is suggested.展开更多
Terrestrial ecosystems represent the second largest carbon reservoir, and the C balance in terrestrial ecosystems can be directly impacted by human activities such as agricultural management practices and land-use cha...Terrestrial ecosystems represent the second largest carbon reservoir, and the C balance in terrestrial ecosystems can be directly impacted by human activities such as agricultural management practices and land-use changes. This paper focuses on the C-sequestration in soil. Although many studies showed that the concentration of SOC is much higher in the shallow soils (0-30 cm), the deeper horizons represent a much greater mass of soil and represent a huge C-storage pool. The process of preferential retention of more strongly adsorbing components, along with competitive displacement of weakly binding components are the key processes that enhance the movement of organic carbon to deeper soil horizons. DOC represents the most dynamic part of organic carbon in soils, and thus can be used as a timely indicator of the short-term change of C-sequestration. Long-term experiments have demonstrated that higher SOC levels in shallow soils would lead to increased fluxes of DOC to deeper horizons, but more data on a wider range of soils and treatment strategies are needed to fully evaluate the linkages between changes in SOC in shallow soil, vertical fluxes of DOC to deeper soil horizons, and enhanced C-inventories in deeper, slow-turnover SOC pools.展开更多
We present a new approach for calculating the C-factor of RUSLE considering the effect of low-reflectance vegetation cover areas on the reduction of the effects on erosion caused by rainfall seasonality.For this,we pr...We present a new approach for calculating the C-factor of RUSLE considering the effect of low-reflectance vegetation cover areas on the reduction of the effects on erosion caused by rainfall seasonality.For this,we propose the coefficients Cr2(rescaled 2)and C-PC(Precipitation Correction),which represent the Cfactor,and an adaptation in NDVI calculation,according to the seasonality of precipitation(NDVI-PC).The Cr2 factor is used when there is no seasonal effect of rainfall on vegetation,while the C-PC factor is calculated for localities under the influence of seasonality,from NDVI-PC.The proposed approaches were tested using different satellites images in the Palmares-Ribeir~ao do Saco watershed,Rio de Janeiro,Brazil.The values of Cr2 and C-PC factors were compared to the Cr factor(rescaled)and to mean values from the literature for different land covers.Our results indicated that the Cr2 factor represents an improvement in accuracy in relation to Cr by considering specific values of the studied area to normalize the data without generalizations.Furthermore,the C-PC factor is able to simulate the effect of seasonality,providing more realistics values of soil loss by the RUSLE as a function of the proportion of area affected by the rainfall seasonality obtained from NDVI-PC.We conclude that both Cr2 and C-PC factors generate values similar of the C-factor observed in the literature,and therefore are able to provide better soil loss estimation than that using the Cr factor.展开更多
文摘A number of very serious drough disasters occurred in many regions of Aftica during past 30 years. It is commonly considered that they are among the most serious disasters after the World War II. The basic situation of the droughs and drough disasters are introduced briefly, and the main causes resulting 1i drought disasters are analysed in the paper. The lack of rainfall is one of the factors producing the drough disasters in Africa, but it is not the real one. From environmental viewpoints, the drough disasters in Africa resulted from unsuitable land use and management by man, and in essence they are the results of man-made environmental disturbance. Finally, the strategy for preventing drought disasters in Africa is suggested.
基金National Science Foundation of the United States the U.S. Department of Agriculture and the U.S. Department of Energy ChinaFLUX
文摘Terrestrial ecosystems represent the second largest carbon reservoir, and the C balance in terrestrial ecosystems can be directly impacted by human activities such as agricultural management practices and land-use changes. This paper focuses on the C-sequestration in soil. Although many studies showed that the concentration of SOC is much higher in the shallow soils (0-30 cm), the deeper horizons represent a much greater mass of soil and represent a huge C-storage pool. The process of preferential retention of more strongly adsorbing components, along with competitive displacement of weakly binding components are the key processes that enhance the movement of organic carbon to deeper soil horizons. DOC represents the most dynamic part of organic carbon in soils, and thus can be used as a timely indicator of the short-term change of C-sequestration. Long-term experiments have demonstrated that higher SOC levels in shallow soils would lead to increased fluxes of DOC to deeper horizons, but more data on a wider range of soils and treatment strategies are needed to fully evaluate the linkages between changes in SOC in shallow soil, vertical fluxes of DOC to deeper soil horizons, and enhanced C-inventories in deeper, slow-turnover SOC pools.
基金Paulo Tarso S.Oliveira was supported by the Brazilian National Council for Scientific and Technological Development(CNPq)(grants 441289/2017e7 and 306830/2017e5)the Coordination of Superior Level Staff Improvement-Brazil(CAPES)(Finance Code 001).
文摘We present a new approach for calculating the C-factor of RUSLE considering the effect of low-reflectance vegetation cover areas on the reduction of the effects on erosion caused by rainfall seasonality.For this,we propose the coefficients Cr2(rescaled 2)and C-PC(Precipitation Correction),which represent the Cfactor,and an adaptation in NDVI calculation,according to the seasonality of precipitation(NDVI-PC).The Cr2 factor is used when there is no seasonal effect of rainfall on vegetation,while the C-PC factor is calculated for localities under the influence of seasonality,from NDVI-PC.The proposed approaches were tested using different satellites images in the Palmares-Ribeir~ao do Saco watershed,Rio de Janeiro,Brazil.The values of Cr2 and C-PC factors were compared to the Cr factor(rescaled)and to mean values from the literature for different land covers.Our results indicated that the Cr2 factor represents an improvement in accuracy in relation to Cr by considering specific values of the studied area to normalize the data without generalizations.Furthermore,the C-PC factor is able to simulate the effect of seasonality,providing more realistics values of soil loss by the RUSLE as a function of the proportion of area affected by the rainfall seasonality obtained from NDVI-PC.We conclude that both Cr2 and C-PC factors generate values similar of the C-factor observed in the literature,and therefore are able to provide better soil loss estimation than that using the Cr factor.
