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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 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 C SOC values in the northeastern region of Chongqing tended to be more negative, whereas those in central Chongqing were less negative. Paddy fields showed the most negative values of δ 13 C 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.

In this study, the effects of gypsum (FGD) on CH 4 emission and functional microbial community in paddy soil were identified under five treatments, including FGDG 0 (0 t·hm -2 ), FGDG 1 (2 t·hm -2 ), FGDG 2 (4 t·hm -2 ), FGDG 3 (8 t·hm -2 ), and FGDG 4 (16 t·hm -2 ). The methane flux was determined using static chamber and chromatography. Bacterial community structure and its effect on soil bacterial community structure, and the abundance of methanogenic and methanotrophs were measured via high-throughput sequencing and quantitative PCR. The results showed that after treatment with desulfurated gypsum, pH of the soil increased significantly ( P <0.05). Redox potential, organic carbon, and available potassium content increased, with no significant difference ( P >0.05). The average emission flux of CH 4 reduced with the increase of desulfurated gypsum content, following the following trend:FGDG 1 > FGDG 2 > FGDG 3 > FGDG 4 . They decreased by 31.56%, 57.30%, 83.60%, and 90.66%, respectively, compared with the control. Compared with the control, FGDG 1 and FGDG 2 increased the richness and variety of soil bacteria. However, when the application amount exceeds 4 t·hm -2 , the richness and variety of soil bacteria decrease. Compared with the control, the relative abundance of sulfate-reducing bacteria in paddy soil increased significantly by 6.98%-13.56%. The abundance of the methane-oxidizing bacteria pmoA gene increased by 0.3%-6.2%. The abundance of the methanogen gene, mrcA decreased significantly by 2.4%-15.8%, while the abundance ratio ( pmoA/mcrA )increased with the increase of the amount of desulfurated gypsum. Correlation analysis showed that the average emission of CH 4 was markedly negatively correlated with the relative abundance of the sulfate-reducing bacteria and pmoA/mcrA percentage in soil, and significantly positively correlated with methanogenic gene, mcrA . In summary, desulfurated gypsum can improve the diversity of bacterial communities and reduce the emission of CH 4 in the paddy soils.

Effect of adding bamboo biochar into the compost at different dosages on greenhouse gas emissions was investigated by analyzing the dynamic characteristics of the process of municipal sludge composting with four different composts (S1:adding 2.5% bamboo biochar, S2:adding 5% bamboo biochar, S3:adding 10% bamboo biochar, CK:without bamboo biochar). The results showed that CH 4 emissions mainly occurred during the heating period and the beginning of the altithermal period, accounting for 99.01%-99.81% of the total emissions. When the added bamboo biochar is less than 5%, CH 4 emissions decrease with the increase in the amount of bamboo biochar. If it is more than 5%, CH 4 emissions will clearly increase. CO 2 emissions mainly occurred during the heating period and the altithermal period, accounting for 75.65%-86.58% of the total emissions. Adding bamboo biochar can reduce 3.37%-13.48% of the CO 2 emissions but there is no significant difference between the treatments ( P >0.05). N 2 O emissions mainly occurred during the heating period and the rotten period. Adding bamboo biochar can reduce the emissions of N 2 O; the more the amount of bamboo biochar, the less N 2 O emissions ( P <0.05). The emission factors of CK, S1, S2, and S3 were 44.10, 37.57, 35.10, and 35.44 kg·t -1 of dry sludge, respectively. S1, S2, and S3 showed 14.81%-20.41% reduction in greenhouse gas emissions owing to the addition of bamboo biochar, indicating that bamboo biochar can reduce the carbon emissions in the process of sludge composting.

Long-term field monitoring data was analyzed regarding the characteristics of nitrogen and phosphorus in the soil and shallow groundwater of different land use types in a typical small watershed of the Three Gorges Reservoir area. Furthermore, the relationships among soil nitrogen and phosphorus contents, concentrations of nitrogen and phosphorus in shallow groundwater, and slope surface runoff were analyzed. The results showed that the average contents of TN and NO 3 - -N in terrace soil were significantly higher than those in sloping upland soil ( P < 0.05), for which the average content of paddy terrace was highest (1.49 g·kg -1 ). The average contents of TP in the soil of sloping upland and mulberry-sloping upland were significantly higher than those in the soil of other land types. The average content of NO 3 - -N in the soil of dryland terrace was highest of all land use types and its discrete degree was also largest. The slope land use type had greater impact on the concentrations of TN and NO 3 - -N in shallow groundwater, but it had little influence on TP concentration. In addition, the shallow groundwater TN concentration and NO 3 - -N concentration had significant positive correlation, and the average contribution rate of NO 3 - -N to TN in five wells ranged from 67.82% to 78.51%. The monthly average concentration of TN and NO 3 - -N in shallow groundwater changed little, only showing a significant upward trend after the fertilization stage of the two crops in spring and autumn. The average contents of TN and NO 3 - -N in the slope soil were significantly correlated with the TN and NO 3 - -N concentrations in the shallow groundwater, but there was no significant correlation between the TN and NO 3 - -N concentrations in the surface runoff. When the slope surface runoff TP concentration was>0.1 mg·L -1 , the average content of TP had a significant linear correlation with it. There was a significant power function relationship between the concentrations of TN and NO 3 - -N in the surface runoff and concentrations of TN and NO 3 - -N in the shallow groundwater, with higher correlation of NO 3 - -N concentrations between surface runoff and shallow groundwater.

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).

Sludge composting is an efficient way to realize the reclamation of waste sludge, while the Green House Gas (GHG) accompanying with it has raised great concern worldwide. However, we do lack the primary data in this area and a great uncertainty of the effect and GHG emission characteristics of sludge composting process in low-temperature environment also exists. This study is aiming to investigate the emission characteristics of GHG from composting in low-temperature environment by applying two different bulking agents to dewatered urban sludge. The results showed that aerobic composting could go smoothly even in an environment with lower temperature, yet the maturity was low due to a sharp drop of pile temperature at the stage of maturing. Sawdust treatment could reduce the total nitrogen loss compared with cornstalk treatment, while its GHG emission equivalence was higher (169.45 and 133.13 kg·t -1 dry sludge, respectively). The accumulative CH 4 emissions of sawdust and cornstalk were 0.648 and 0.689 kg·t -1 dry sludge, respectively, of which over 75% was from the first two weeks; total N 2 O emissions of sawdust and cornstalk were 0.486 and 0.365 kg·t -1 dry sludge, of which more than 90% came from the decomposting process. On the whole, because of the relatively short duration of high temperature as well as the low temperature during mature stage, the process had an especially low emission of CH 4 but a relatively high discharge of N 2 O. For composting in low-temperature environment, necessary measures should be taken to control N 2 O emission in the late period in order to realize GHG reduction.

As a key geochemical factor in earth system, dissolved organic matter (DOM) plays an important role in controlling environmental quality of watersheds. In this study, a typical agricultural watershed of Three Gorges reservoir areas, Wangjiagou watershed in Fuling district of Chongqing, was selected to characterize DOM in waters through fluorescence and UV-Vis spectroscopy, while the effect of land-use types in this watershed was discussed. The results showed large spatial variances of aquatic DOM in this watershed, with significant differences in compositions and sources. After calculation of a g * (355) for indicating proportion of chromophoric DOM in bulk DOM, the order of DOM was paddy rice field> ditch> pond> well> outlet point. DOM samples from paddy rice field and ditch showed higher SUVA 254 suggesting higher aromaticity. DOM from this watershed showed 2 typical types (4 peaks A, C, B and T) of fluorescent components including humic-like and protein-like components. Dual contributions from autochthonous (e.g., microbial or alga production) and allochthonous both heavily affected the DOM characteristics. Besides active microbial activities due to high organic and nutrients inputs from agricultures, discharge of sewage and water used in agricultural production could contribute proteins possibly inducing ascending proportion of protein-like component as shown in fluorescence analysis. DOM samples from the same sampling points but in different crop plantation seasons were collected to compare, for understanding the differences between two planting seasons. It clearly suggested protein-like component was the key variable to control the DOM dynamics. After land-use changing from rice/corn into mustard plantation, all of DOC, CDOM and r (T/C) showed significant differences, but no such observations were observed in FI, BIX and r (A/C) .

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%.

The temporal and spatial distribution of mercury (Hg) in four different sources of stream (aquaculture wastewater, bare land, forestry land and agro-forestry land) and well water of an agro-forestry and livestock compound watershed in the Three Gorge Reservoir region was studied during the period from March 2013 to March 2014. The total mercury (THg) concentrations ranged 9.95-15.26 ng x L(-1) with an average of (11.95 +/- 1.87) ng x L(-1), and the THg concentration decreased in the order of bare land > aquaculture wastewater> forestry land > agro-forestry land > well water. The total methylmercury (TMeHg) concentrations ranged 0.120-0.441 ng x L(-1) with an average of (0.232 +/- 0.099) ng x L(-1), and the TMeHg concentration decreased in the order of aquaculture wastewater > agro-forestry land > forestry land > bare land > well water. THg and TMeHg in well water were both dominated by the dissolved fraction, whereas for other sources of stream, the particulate phase accounted for the major fraction of THg and TMeHg. The THg concentrations in winter and spring were significant higher than those in summer and fall, however, no obvious seasonal trend of TMeHg distribution was observed. Comprehensive analysis showed human activities and weather conditions such as air temperature and precipitation etc. were the main reasons for the difference of temporal and spatial distribution of THg and TMeHg.

The distribution of mercury (Hg) in four different water bodies (streams, pond, precipitation and wells) of a small typical agricultural watershed in the Three Gorges Reservoir region was studied during the period from November 2011 to September 2012. Total mercury (THg) and methylmercury (TMeHg) concentrations ranged from 1.12 ng x L(-1) to 64.04 ng x L(-1) and from 0 (undetected) to 4.24 ng x L(-1), with an average of (13.54 ± 10.55) ng x L(-1) and (0.22 ± 0.42) ng x L(-1), respectively. Particulate mercury (PHg) accounted for a major fraction of THg in these four water bodies, whereas for TMeHg dissolved fraction dominated in wells and streams, but not in pond and precipitation. An obvious spatial pattern of Hg distribution was observed with THg concentration in the order of precipitation > pond > streams > wells and streams > pond > precipitation > wells for TMeHg. The THg temporal distribution showed that THg concentrations in cold season were higher than that in warm season, but the temporal distribution of TMeHg varied with the water types. Comprehensive data analysis found that wet deposition was a significant source of Hg in this agricultural watershed and the particulate transport was the main way for Hg and MeHg transport in this watershed. In addition, surface runoff was an important process for Hg contribution from watershed to the Three Gorges Reservoir, but played a minor role for TMeHg load to the reservoir.