Do land use change and check-dam construction affect a real estimate of soil carbon and nitrogen stocks on the Loess Plateau of China?
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Soil carbon
Loess plateau
Shrubland
Collapsible loess is widely spread in Loess Plateau, northern Shaanxi province. The constructional damage due to side slope and irrigation will be caused if the loess doesn't deal with properly. Based on the analysis features of loess collapsibility and numbers of lab tests, this paper presents the relationship between loess structural parameters and confining pressure, as well water content and porosity ratio. The relevant loess structural parameters were obtained by fitting method. The loess collapsibility characteristics were analyzed with different confining stress, soil water content and porosity ratio. The main triggering factors of loess collapse were also analyzed. The results can further give the scientific evidence when dealing with the collapsible loess.
Loess plateau
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Yili area is located in the west of Xinjiang and is an intermountane basin of Tianshan, in which the loess is widespread. Only a few studies were carried out during past decades. For this reason, there are different opinions on the origin of loess. The results of grain size analysis of loess and reworked loess show that the textural features of both are same on one side and different on the other side. Firstly, the composition of grain size of loess is similar to that of the reworked loess, but the sand particles of loess is higher and the clay particles is lower than that of reworked loess. Secondly, the frequency curve of loess and reworked loess occures to be positive normal distribution. The mode of both locates in the range of 15-30μm, but the percentages are different. The amount of loess is less than 20 %, while the maxmum percentage of reworked loess reaches 50 %. Thirdly, the sorting of loess is better than that of the reworked loess, even though both are poor sorting deposits. The skewness of loess ranges from 0. 13 to 0. 43 and most of them is lower than 0. 3. Comparied with the loess, the skewness of reworked loess is higher and the mediun size moves toward coarse side. The kurtosis of loess is medium, while peak of reworked loess is steep. In summary, the loess and the reworked loess were transported and sorted by different dynamics before the dust deposited. In addition, the depositing environments were also different. The evidences from the grain size show the loess in Yili area is a typical eolian deposit.
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Shrubland is an important type of vegetation in the semi-arid region of the western Loess Plateau, and it is of great value to the maintenance of biodiversity and soil and water conservation. Equally, there may be significant differences in the level of diversity and the community assembly patterns across different types of shrublands (desert, alpine, and secondary shrublands). This study aimed to reveal the diversity and the community assembly patterns of different types of shrublands and the environmental explanations for these by using a taxonomic and phylogenetic analysis approach, as well as by considering soil and climate factors. The diversity level of the desert shrublands was low, and the habitats of the three types of shrubland were significantly different. Precipitation may be the main environmental factor driving the variation in and diversity of these types of shrubland. All three types of shrubland were strongly affected by environmental filtering and competitive exclusion, and their community assembly patterns were similar.
Shrubland
Loess plateau
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By simulating the climate features on loess plateau,the loess ground thermal regime is deriked.By analyzing the calculated data and the tested data for the thermal regime,the changing law of the thermal regime caused by climatic change is explored.The relationship between loess temperature and loess depth in any month is given.It is pointed that the less the loess depth,the more the variation of temperature caused by climate change,and the more is the highest temperature and the less the lowest temperature.Further,this paper indicates that the more the loess depth is,the less is the variation of loess temperature caused by climate change.And the formula,by which the variation of loess temperature in any depth can be calculated,is arrived at.
Loess plateau
Variation (astronomy)
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The loss of shrubland habitat is linked to population declines for many wildlife species, including several bird species of conservation concern. Conservation agencies in the northeastern United States encourage private landowners to clearcut patches of forest to create shrubland habitat. Many private landowners are only willing to create small clearcuts; therefore, it is important to understand how to maximize the impact of small clearcuts on bird habitat use. In this study we examined whether proximity to wetland shrubland increases the habitat value of small patches of upland shrubland. We conducted point counts at 22 sites containing small patches of upland shrubland ranging in size from 0.1 to 7 ha. Shrubland bird species richness was significantly positively correlated with the proportion of wetland shrubland habitat within 100 m of a site, and with the extent of all shrubland habitat within 100 m, but not with the proportion of upland shrubland. Occupancy modeling indicated that the size of adjacent wetland shrub patches increased occupancy at the sites for five of eight species observed with sufficient rates of detection. Our results suggest that creating clearcuts adjacent to existing areas of wetland shrubland may enhance the habitat value of the patches for shrubland birds.
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Soil organic carbon(SOC) storage and its change trend in China is important to the global carbon cycles under the background of global warming.Land use change has both direct and indirect influences on SOC storage.On the one hand,the land use change directly modifies the original ecosystem type and then makes the net primary productivity and soil carbon input change,which directly impacts SOC storage.On the other hand,land use change modifies some physical or chemical properties of soil and thus potentially impacts the value of temperature sensitivity of soil heterogeneous respiration(Q_(10)). Under the situation of global warming,the changed Q_(10) will modify the feedback intensity of soil respiration and then indirectly impacts the soil organic carbon storage.In this study,a regional process-based carbon cycle model(CASA model) was used to estimate the Q_(10) values for the different land use types.Basing on the differences of Q_(10) among land use types,the indirect impacts of land use change on soil organic carbon storage was assessed.The results showed that the land use changes from grassland or forest to cropland will increase the value of Q_(10).Furthermore,the human activities,such as utilizing of irrigation and nitrogenous fertilizer will also increase the values of Q_(10).So,the land use change and human activities will potentially increase soil carbon releasing under the situation of global warming and then will indirectly impact soil organic carbon storage.
Soil carbon
Global Change
Soil respiration
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Soil carbon sequestration and land use change associated with biofuel production: empirical evidence
Abstract Soil organic carbon ( SOC ) change can be a major impact of land use change ( LUC ) associated with biofuel feedstock production. By collecting and analyzing data from worldwide field observations of major LUC s from cropland, grassland, and forest to lands producing biofuel crops (i.e. corn, switchgrass, Miscanthus , poplar, and willow), we were able to estimate SOC response ratios and sequestration rates and evaluate the effects of soil depth and time scale on SOC change. Both the amount and rate of SOC change were highly dependent on the specific land transition. Irrespective of soil depth or time horizon, cropland conversions resulted in an overall SOC gain of 6–14% relative to initial SOC level, while conversion from grassland or forest to corn (without residue removal) or poplar caused significant carbon loss (9–35%). No significant SOC changes were observed in land converted from grasslands or forests to switchgrass, Miscanthus, or willow. The SOC response ratios were similar in both 0–30 and 0–100 cm soil depths in most cases, suggesting SOC changes in deep soil and that use of top soil only for SOC accounting in biofuel life cycle analysis ( LCA ) might underestimate total SOC changes. Soil carbon sequestration rates varied greatly among studies and land transition types. Generally, the rates of SOC change tended to be the greatest during the 10 years following land conversion and had declined to approach 0 within about 20 years for most LUC s. Observed trends in SOC change were generally consistent with previous reports. Soil depth and duration of study significantly influence SOC change rates and so should be considered in carbon emission accounting in biofuel LCA . High uncertainty remains for many perennial systems and forest transitions, additional field trials, and modeling efforts are needed to draw conclusions about the site‐ and system‐specific rates and direction of change.
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The loess tunnel, a kind of subground erosional geomorphy, is common in the loess plateau. Firstly, the classification of loess tunnels in the loess plateau is introduced. Secondly, based on field research, the distribution regularity of loess tunnels is discovered, that is, the density of loess tunnels is becoming lower from the north-west to the south-east. Thirdly, both the loess types and density differ in different depth; finally, the benefits and hazards of loess tunnels are analyzed. Results show that the loess tunnel has double significance: on the one hand, as a kind of geological hazard, it can not only result in serious water and soil loss, but also make damages to various constructions such as highway, railway, oil and gas conveying pipes and folk houses. On the other hand, it is a kind of important way that provides and discharges water for the effluent reservoirs in the loess plateau.
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