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Soil was sampled from 182 profiles in typical farmlands of Chongqing and analyzed for the stable carbon isotope composition of organic matter ( δ 13 C SOC ). The results showed that the values of δ for each soil profile were gradually increasing with increasing soil depth, and the mean values were (-23.63±1.53)‰, (-22.43±1.59)‰, and (-21.42±1.90)‰ for surface, middle, and bottom layers, respectively. The 13 C SOC for each soil profile were gradually increasing with increasing soil depth, and the mean values were (-23.63±1.53)‰, (-22.43±1.59)‰, and (-21.42±1.90)‰ for surface, middle, and bottom layers, respectively. The δ 13 , followed by rice-upland rotating fields and upland fields, with the average being (-25.32±0.93)‰, (-23.17±1.37)‰, and (-24.75±1.28)‰ for the surface layers, respectively. For different soil types, the SOC C values in the surface layers were in the order of paddy soil13 in surface soils, and soil types mainly affected that in the middle- and bottom-layer soils. Other factors, such as soil properties (TN, SOC, and pH) and meteorological conditions (precipitation and air temperature) played only minor roles in the variation of SOC , followed by rice-upland rotating fields and upland fields, with the average being (-25.32±0.93)‰, (-23.17±1.37)‰, and (-24.75±1.28)‰ for the surface layers, respectively. For different soil types, the δ 13 C values in the surface layers were in the order of paddy soil13 C SOC in surface soils, and soil types mainly affected that in the middle- and bottom-layer soils. Other factors, such as soil properties (TN, SOC, and pH) and meteorological conditions (precipitation and air temperature) played only minor roles in the variation of δ 13 C SOC . In short, the stable isotope composition of organic carbon in the surface soils was primarily controlled by the input carbon source, whereas that in the deeper layers was closely linked with carbon cycling processes within the soils.

Effect of application of sewage sludge compost on the emission of greenhouse gas from soil was investigated by analyzing the dynamic characteristics and emission factor of CO 2 , CH 4 and N 2 O in soil after spiking two different composts (A:compost with biochar, B:compost without biochar) with varying fertilizing amount into soil. The results indicated that emissions of CO 2 and CH 4 mainly occurred in the plant growth period with low fertilizer amount of biomass charcoal compost reducing CO 2 emissions, and high application content increasing CO 2 emissions. CH 4 emission fluxes showed negative values, indicating that soil could adsorb CH 4 , and the adsorbing amount for control was significantly higher than those for other treatments ( P <0.01). The absorbing amount in treatment A increased with the fertilizing amount ( P <0.05). N 2 O emissions mainly occurred at the germination and seedling stages, and emission fluxes increased with the fertilizing amount ( P <0.01). N 2 O was considered as the main generated greenhouse gas during agricultural process with sludge compost, and its emission factor from sludge compost soil was 1.02%-1.90% (A compost) and 1.28%-2.93% (B compost), respectively. Biochar could significantly reduce the carbon emission, as the total greenhouse gas released from soil with biochar compost was 19.49% to 35.56% less than that in soil without biochar, which was more obvious for N 2 O emission reduction (compared with CH 4 mitigation).

Phthalic acid esters (PAEs) have received increasing attention in recent years due to their widespread use and hazards to human health and fertility in the environment. In order to understand the migration and release processes of organic pollutants in huge fluctuating zone soil, Dibutyl-phthalate(DBP) was chosen as a typical substance, and its migration and release characteristics in the fluctuating zone of the Three Gorges Reservoir to overlying water and the impacts of DBP concentration in the soil, ionic strength and the concentration of organic mater in overlying water on the process were studied using static flooding method. The results showed that DBP migrated from the soil to the overlying water in the early days after flooding, and the release process of DBP was divided into two phases: one was quick release with a relatively short releasing time and a rapid releasing rate; the other was slow release with a relatively long releasing time and a slow releasing rate. The migration and release processes were well fitted by two-compartment first-order kinetics. After different concentrations DBP were added into soil, the rate of quick release increased with the increasing DBP concentrations in soil while the percent of quick release decreased with the increasing DBP concentrations. The results of rate of slow release and the percent of slow release were on the contrary. The water conditions of overlying water could impact the migration and releasing process of DBP when the soil in fluctuating zone was flooded. The amount of DBP released into the overlying water would increase when the ionic strength in the water increased. At the same time, when the ionic strength increased, in spite of the decreasing quick release rate, the percent of quick release increased. The higher concentration of organic matter in overlying water, the more the amount of DBP released into the overlying water. At the same time, all of the rates of quick release, slow release and the percent of quick release would increase with the increasing concentrations of organic matter, while there was almost no influence on the percent of slow release of DBP.

As an important geo-factor to decide the environmental fate of pollutants in watershed, soil dissolved organic matter (DOM) sampled from a typical agricultural watershed in the Three Gorges Reservoir area was investigated using ultraviolet-visible (UV-Vis) and fluorescence spectroscopies, to analyze and discuss the effect of different land uses including forest, cropland, vegetable field and residence, on soil DOM geochemical characteristics. The results showed that significant differences in DOM samples amongst different land uses were observed, and DOM from forest had the highest aromaticity and humification degree, followed by DOM from cropland. Although DOM from vegetable field and residence showed the highest dissolved organic carbon (DOC) concentration (average values 0.81 g x kg(-1) and 0.89 g x kg(-1), respectively), but the aromaticity was lower indicating lower humification, which further suggested that the non-chromophoric component in these DOM samples contributed significantly to total DOM compositions. Additionally, in all DOM samples that were independent of land uses, fluorescence index (FI) values were between 1.4 (terrigenous) and 1.9 (authigenic) , evidently indicating both the allochthonous and autochthonous sources contributed to DOM characteristics. Meanwhile, r(T/C) values in most of samples were higher than 2.0, suggesting that soil DOM in this agricultural watershed was heavily affected by anthropogenic activities such as agricultural cultivation, especially, vegetable field was a good example. Additionally, sensitivities of different special spectral parameters for reflecting the differences of DOM characteristics amongst different land uses were not identical. For example, neither spectral slope ratio (S(R)) nor humification index (HIX) could clearly unveil the various geochemical characteristics of soil DOM from different sources. Thus, simple and single special spectral parameter cannot comprehensively provide the detailed information of DOM, and combined application of UV-Vis and fluorescence spectroscopies is highly recommended.

In order to understand the environmental behavior of the organic pollutants Dibutyl-phthalate (DBP) in fluctuating zone soil, the migration and release processes of DBP in the fluctuating zone of the Three Gorges Reservoir to the overlying water and the impacts of temperature, light, coexistence phthalate-bis (2-ethylhexyl)-ester (DEHP), microbial activity on the process were studied using static flooding method. The results showed that DBP migrated from the soil to the overlying water in the early days after flooding, and the release process of DBP was divided into two phases: one was the quick release with a relatively short releasing time and a rapid releasing rate; the other was the slow release with a relatively long releasing time and a slow releasing rate. The slow release was a major speed control step, which could be well fitted by two-compartment first-order kinetics. In the interim (12 d) after flooding, the capacity of release reached a maximum, the DBP released from the soil into the water migrated from the water to the soil again after continued flooding, and eventually the content of DBP in soil and water reached equilibrium in the later period after flooding. The intensity of DBP releasing into the overlying water and the rapid releasing rate increased, while the slow releasing rate decreased when the temperature increased. The concentrations of DBP released into the water were different with different light sources. The concentration of DBP in the overlying water with treatment of natural light was higher than those with treatment of ultraviolet light UVB, UVA. After the amount of DBP in the overlying water reached the maximum, the content of DBP in the overlying water decreased relatively faster under the ultraviolet light than under the natural light. The largest release content of DBP and the time reached the largest release content were different with different oxygen content in the overlying water. Overall, the higher oxygen content in the overlying water, the higher content of DBP in the overlying water. The time when the concentration of DBP in overlying water reached the maximum was on the 8th day after flooding in the high oxygen and low oxygen studies, while the time was on the 12th day in natural study. When the phthalate-bis (2-ethylhexyl)-ester(DEHP) co-existed in the soil, there would be some significant influence on the release of DBP. After DEHP addition in the soil, it could release more DBP than the control, and both the rapid releasing rate and slow releasing rate were bigger than those of the control. The microbial activity had some impacts on the process. However, the effect was not obvious. After adding microbial activity inhibitor, the content of migrated DBP was slightly lower than that of the control.

To understand the mercury (Hg) pollution level and the corresponding ecological risk in agricultural watershed of the Three Gorges Reservoir region, a typical watershed, Wangjiagou, located in Fuling, where is in interior zones of the Three Gorges Reservoir region, was selected as the study object. Meanwhile, ArcGIS geo-statistics module was conducted for investigation of the Hg contents and distribution characteristics in soils of different land use types including dry land, farmland, woodland and settlements. Also the corresponding Hg pollution level and ecological risk were assessed. The results suggested that soil Hg contents in this watershed ranged from 9.47 to 94.57 microg x kg(-1), and the mean value was (34.23 +/- 16.23) microg x kg(-1). Higher Hg contents in surfaces of soils were observed in woodland, followed by farmland and settlement. The lowest was found in dry land. Surfaces of soils significantly showed Hg accumulation, and an obvious inverse correlation between soil Hg contents and soil depths was also observed in this study. Additionally, geo-statistics analysis showed a weak spatial correlation of soil Hg contents in this watershed, indicating the spatial distribution of soil Hg in this watershed was mainly influenced by several natural factors such as atmospheric wet-dry deposit, vegetation coverage and topography, instead of anthropogenic interference. Overall confirmative soil Hg pollution was not found in this watershed, which showed a very low pollution index (-0.08), but a moderate potential ecological risk still existed (the ecological risk index was 57), of which woodland had the highest potential risk. The total capacity of Hg in this watershed was 25.39 kg, among which dry land accounted for 69%.