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[Objective] The main controlling factors of soil organic carbon mineralization and its temperature sensitivity(Q10) for municipal sludge resource utilization and soil carbon pool stability after sludge compost application were revealed, which provided theoretical support for municipal sludge treatment and soil organic carbon sequestration. [Methods] In the present study, different doses of composted sludge (0, 2.0%, 5.0%, 10.0%, 15.0%, and 20.0%) were added to the degraded grassland soil collected from the loess hilly area, and the soil organic carbon mineralization rates under different incubation temperatures (15℃, 25℃ and 35℃) were measured. The effects of composted sludge addition on soil organic carbon mineralization characteristics and Q10 values were discussed. [Results] Compared with CK, the soil organic carbon mineralization rate significantly (p＜0.01) increased with composted sludge addition doses at the initial stage of cultivation, and then it rapidly decreased until it reached to a stable value. The cumulative soil organic carbon mineralization under the composed sludge addition treatments were 1.6～4.2 times greater than that of CK. When the composed sludge application doses were between 10.0% and 20.0%, the organic carbon mineralization rate and cumulative mineralization amount had no significant difference. The first-order kinetic equation was used to fit the dynamics of soil organic carbon mineralization with composted sludge addition treatments at different incubation temperatures and achieved good results (R²＞0.95). Soil organic carbon mineralization potential (C0) values ranged from 6.92 to 39.60 mg C/g and the differences were significant (p＜0.05) among different treatments. The soil organic carbon mineralization kinetic constant (k) ranged from 0.03/d to 0.12/d, and it was significantly correlated with incubation temperatures (p＜0.01). The Q10 values ranged from 1.18 to 2.58 with the composted sludge application doses, and the Q10 reached the maximum value when the application doses reached 10.0%, and then the Q10 values decreased with the doses of the composed sludge addition. [Conclusion] When the composted sludge application doses are at 10.0%～20.0%, the content of soil organic carbon can obviously increase, inhibit the re-mineralization of soil organic carbon, effectively adjust soil Q10, and ensure the relative stability of soil carbon pool, which is beneficial for the sequestration of soil organic carbon. [ABSTRACT FROM AUTHOR]

Seasonal freezing-thawing phenomenon occurs mainly in mid-latitudinal region, which is generally characterized by freezing in winter and melting in summer. The middle reaches of the Yellow River are in the middle latitudes, and their climatic conditions meet the requirements of freeze-thaw erosion. The soil erosion during thawing period is a special form of erosion in winter and spring, which is often caused by the combination of water erosion, gravity erosion and freeze-thaw erosion. During the soil thaw period, due to the poor thawing of slope soil and poor permeability, severe soil and water loss occurred under very small rainfall intensity. Domestic studies on soil erosion in thawing seasons are mainly concentrated in the northeastern region. However, there are few studies on the Loess Plateau region in the northwest, and few experiments have been conducted to quantitatively study freeze-thaw erosion on the Loess Plateau. Therefore, in order to study the effect of rainfall on the permafrost slope erosion on the Loess Plateau, the difference of erosion between permafrost and unfrozen soil under different hydraulic conditions is clarified. Through the indoor simulated rainfall experiment, 3 kinds of rainfall intensities (0.6, 0.9, 1.2 mm/min) and 2 kinds of slopes (frozen soil slope and control slope) were used to quantitatively study the process of runoff and sediment yield on slope as well as the relation between the runoff and the sediment under different experimental treatments. The results showed that the time producing runoff on the frozen soil slope was 18.70 and 6.44 min earlier than the control slope under the rainfall intensity of 0.9 and 1.2 mm/min, respectively. The runoff and erosion amount of the frozen soil slope were far greater than that of the control slope. The runoff at the rainfall intensity of 0.9 and 1.2 mm/min was 1.16 and 1.19 times that of the control slope respectively, and the erosion amount was 10.39 and 6.39 times respectively. As the rain went on, the slope produced different degrees of rill. The occurrence time of rill on frozen slope was shortened by 18 and 22 min, respectively, compared with the control slope, and the rill erosion on frozen soil slope accounted for 79.33%-92.02% of the total erosion amount, which was greater than that of the control slope under the same rainfall intensity. The cumulative runoff and accumulated sediment yield of the 2 slopes satisfied the linear relationship of y=kx+b, and the k value of the frozen soil slope was 8.48-9.02 times that of the control slope in the inter-rill erosion stage, while 3.68-7.50 times in the rill erosion stage. The results showed that the rill erosion was the main reason to the increase of soil erosion rate on the frozen soil slope, and the water blocking effect of the freezing layer was the most important factor leading to the advance of the emergence time of rill on the slope. This result is expected to provide some certain reference for the study of soil erosion mechanism. [ABSTRACT FROM AUTHOR]

In order to reduce soil erosion and improve ecological environment, the Chinese government implemented the Grain for Green Project in 1999, in which numerous croplands were converted to grasslands, forestlands, or free land for natural plant succession. The ecological construction not only significantly changes the vegetation cover conditions of the watershed, but also changes the hydrological processes of the watershed. In order to understand the changes of ecological and hydrological processes under different ecological construction conditions, 414 water samples were collected in the governance river basin of Jiuyuangou Watershed and 300 water samples were collected in the natural river basin of Peijiamao Watershed, which are sub basins of Wuding River. The water samples included precipitation, river water, well water, reservoir water and snow water. Each water samples had three replicates. Based on stable isotope technology, the hydrogen and oxygen isotope characteristics were analyzed in different water samples. The effects of ecological construction on water transmission process and transformation characteristics between different water bodies in different seasons were also evaluated in this research. The results showed that the amplitude of precipitation isotope values were greater than the river water and well water isotope values. In addition, the river water and reservoir water had stronger evaporation fractionation than other water samples and well water was relatively stable. The local meteoric water line was δD=7.09δ18O+1.29 in the governance river basin of Jiuyuangou watershed and δD=6.71δ18O-3.25 in the natural river basin of Peijiamao watershed. The slope and intercept of the local meteoric water line in Jiuyuangou watershed was greater than that in Peijiamao watershed. The water supply source of river water, well water and reservoir water were mostly from precipitation. At the same time, precipitation and snow water had similar sources. During the dry season (from December to June), the temperature was low and during the wet season (from July to November), it was high, and the precipitation was mainly distributed in June to November. The isotope values were low in the wet season, and dry season isotope values were high. The isotope values were positively correlated with the precipitation, and negatively correlated with the temperature. The isotope values of river water and well water showed a similar trend of variation, which became enrichment with the main channel flow. The oxygen isotope value was used to calculate the supply ratio of precipitation, river water and well water in dry season and wet season. In dry season, precipitation and well water supplied river water, and the supply ratio was 24.66%, 75.34% and 83.81%, 16.19%, respectively. In wet season, well water was supplied by precipitation and river water, and the supply ratio was 14.75%, 85.25% and 48.06%, 51.94%, respectively. Ecological construction had significantly changed the ecological and hydrological processes. The acceleration of ecological construction had a significant impact on the transformation of different water bodies in the river basin of Loess Plateau. The present research could provide technical support and theoretic foundation for the study of ecological and hydrological processes and ecological environment protection on the Loess Plateau. [ABSTRACT FROM AUTHOR]