Soil water plays an important role in the critical zone water cycle,and the results of soil water content observation can in some way affect the allocation of water resources,determination of agricultural practices,and development of environmental disaster forecast. Cosmic ray neutron probe (CRNP)method,which measures soil water content by monitoring the change of neutron current in the near surface cosmic ray,has advanced rapidly in the last decades. The fundamental theories of using CRNP into soil moisture monitoring are introduced. The method has a support volume at hundred-meter (horizontal)and decimeter (vertical)scale,which fills the gap between field sampling and remote sensing. The sensor response is not only influenced by soil water,but other hydrogen reservoirs near land surface,and even within the support volume these factors still don't contribute evenly. Therefore,interpretation of the sensor response,which includes determination of the exact range of the support volume,allocation of spatial weighting factors within the support volume,and calibration of the impacts of atmosphere,soil and vegetation,remains the critical work during the development of the method;and a number of researchers have continuously contributed on it. The current utilization of the method in agricultural management,hydrological modeling and meteorological forecast is enumerated,and existing problems and possible development directions in future are also discussed. By the synthesis of the related work,it is expected to promote a further and extensive application of this method into the above areas.

Nitrous oxide (N₂O)is one of the major greenhouse gasses. In atmosphere,the concentration of N₂O is increasing sharply. Agricultural soil is a major source of N₂O emissions,accounted for approximately 70% of total global anthropogenic emissions. Nitrification,denitrification,nitrifier denitrification and dissimilatory nitrate reduction to ammonium are the main N₂O generation processes. Based on clarifying of the N₂O generation mechanisms,the development and research status of the process-based mechanism models[including denitrification-decomposition (DNDC),water and nitrogen management model (WNMM),DAYCENT and ecosystem model (Ecosys)]for N₂O emissions from agricultural soil were reviewed and summarized. Some key issues that should be paid more attention in the future studies on the N₂O emission simulation for agricultural soils,including the model mechanism improvement,parameter adjustment and enhancement of the regional simulation ability. Research on the cropland N₂O generation mechanism and related models is meaningful to predict and mitigate the N₂O emissions and maintain the ecological balance.

Dissolved organic matter (DOM)is a photochemically active material widely found in the water environments and regulates energy and material flows in ecosystems. Containing a variety of chromophores,DOM irradiated with sunlight can be photobleached and photomineralized and generate various reactive species,such as ³DOM^*,H₂O₂,¹O₂,and HO^·. These photochemical transformation processes tend to alter the microbial activity,pollutants transformation,and water quality. The source,composition,structure and properties of DOM are extremely complex,which leads to complicated photochemical behaviors and effects of DOM. To date,the relevant understanding is still lacking but constantly evolving. Here,the research advances on the photochemical behaviors of DOM and its important environmental effects were reviewed. To broaden the research object of DOM,to establish the DOM structure-photochemical reactivity relationship models,and to elucidate the influence of environmental factors on DOM photochemical effects and its mechanism were also proposed.

Ecological security patterns are important for the optimal allocation of ecological resources,and for restricting the expansion of cities. In order to implement effective protection for maintaining ecological safety in urban agglomeration,it is important to plan and support regional green space. Currently,technical difficulties in studying ecological security patterns are linked to the identification of ecological sources and the construction of spatial resistance surfaces. RS and GIS technology were used to identify ecological landscape types and landscape patterns in the urban agglomeration of the Greater Bay Area using data from 1980,1995 and 2010. Ecological source patches were identified by evaluating ecosystem service importance. A regional ecological network was constructed using the minimum cumulative resistance model and the layout of eco-spatial structure in the region was optimized. Results show that: (1)forestland was the dominant landscape in the study area. The land-use landscape tended to be unstable,with fragmentation increasing and the index of COHESION and AI of farmland and forestland decreasing; (2)the area of ecological sources was approximately 2 638.3 km²,with the ecological source areas accounting for 9% of the forestland. The key ecological corridors,distributed in a branch shape with a radial pattern,were 705 km long. Although the overall ecological environment has improved, distribution was uneven,especially for the connectivity of the ecological corridors to the east of the Pearl River area; (3)in order to enhance the integrity and penetration of the natural ecosystem,it is proposed that to construct a high quality continuous forest based on the northern mountainous ecological barrier and the southern coast forest. At the same time, it is important to coordinate the construction of a cross-regional forest barrier belt to improve connectivity of ecological sources and to enhance regional ecosystem services.

In river network areas,the control of agricultural non-point source pollution (ANPSP)should consider not only the pollutant removal effect and cost but also the resource utilization efficiency. Taking Xinjian Town,Yixing City on the west bank of Taihu Lake as an example,the volume of wastewater and the pollutant loads discharged from three pollution sources (crop farming,livestock and aquaculture)were investigated. The demand of water for irrigation and the potential reuse of wastewater for irrigation and the potential reuse of nitrogen (N)and phosphorus (P)from manure and wastewater for fertilizing cropland were also estimated. The performance of two schemes of ANPSP control system (Scheme I:reuse of all livestock wastewater and manure;Scheme Ⅱ:reuse of all livestock wastewater and manure and some aquaculture wastewater)on pollutant reduction efficiency (TN,TP,NH₃-N,and COD)and economic cost were evaluated. The results show that if all the livestock wastewater (71.96×10³ m³) and some aquaculture wastewater (2 277.11×10³ m³)were reused for irrigation after processing could meet the total irrigation water demand in Xinjian Town (Scheme Ⅱ). The removal efficiencies of Scheme Ⅱ for the pollutants TN,TP,NH₃-N,and COD were 84.3%, 94.2%,89.6% and 94.0%,respectively. In addition,Scheme Ⅱ could reduce the use of chemical fertilizers by nearly 81.8 kg·hm^-2 of N and 39.9 kg·hm^-2 of P annually. In order to reduce costs,Scheme I that only reuse livestock wastewater (71.96×10³ m³)for irrigation after processing could only meet with 3% of irrigation water demand. The removal efficiencies of Scheme I for the pollutants TN,TP,NH₃-N,and COD were 83.0%,93.7%,88.7% and 93.7%,respectively,and the use of N and P fertilizers can be reduced by nearly 52.0 and 34.2 kg·hm^-2 annually. The proposed two schemes of ANPSP control system with consideration of nutrients and wastewater recycling may provide a reference for the construction of pollution control projects in Xinjian Town.

To investigate the characteristics and changes of rural residential forests of Linghe town,a typical rural area in mid-south of Shandong Province,13 new villages and 11 old villages as research objects were selected. Plant investigation and plant culture interview were carried out first,then the canopy coverage rate,plant landscape and human characteristics were analyzed,and finally these characteristics between new villages and old villages were compared. The results show that: (1)The overall canopy coverage of Linghe town was 1 213 875.7 m² and canopy coverage rate was 10.05% in 2016,which was lower than that in 2012;specifically from 16.86% in 2012 to 11.18% in 2016 in new villages while from 12.50% in 2012 to 9.07% in 2016 in old villages. (2)Populus spp.,Cerasus yedoensis,Paulownia fortunei,Diospyros kaki,Toona sinensis,Chaenomeles cathayensis,Robinia pseudoacacia dominated the overall rural landscape,where Populus spp. accounted for the majority. Besides,comparing to old villages,riparian view in new villages exhibited similar patterns. Populus spp.,Paulownia fortunei,Robinia pseudoacacia,Sophora japonica,Salix babylonicawere decreased in courtyard landscape,but Cerasus yedoensis,Platanus acerifolia,Chaenomeles cathayensis,Toona sinensis were increased in courtyard landscape,while Diospyros kaki kept stable in that. Moreover Populus spp.,Sophora japonica,Robinia pseudoacacia,Salix babylonica,Albizia julibrissin were decreased in road landscape,but Cerasus yedoensis, Magnolia grandiflora,Chaenomeles cathayensis,Lagerstroemia indica,Platanus acerifolia were increased in road landscape,while Diospyros kaki stayed the same in the road landscape. (3)Human characteristics of rural residential forest include three types,i. e.,aesthetic appreciation,food supplement and emotional implication. Amongst,aesthetic appreciation and food supplement were the primary needs of courtyard forests in new and old village,while emotional implication needs was gradually reduced in courtyard forests,road forests and riparian forests.

The surface sediments collected from major lakes located in Guangzhou City were analyzed for the concentration and spatial distribution of Cd,Cr,Cu,Ni,Pb and Zn. The pollution and potential ecological risk of which were assessed using the methods of geo-accumulation index,enrichment coefficient and potential ecological risk index. The results show that the concentrations of Cd,Cr,Cu,Ni,Pb,and Zn were 0.50-6.90,36.00-197.40,32.35-432.00, 17.35-155.50,32.50-162.70,71.83-853.40 mg·kg^-1,with average of 2.54,92.27,165.20,70.21,90.48, 447.88 mg·kg^-1,respectively,being significantly higher than those of background values in soils of Guangdong Province. As for spatial variation,the concentrations of heavy metals were higher in Baiyun Lake and Dongshan Lake than those of Liuhua Lake and Huadu Lake. Based on geo-accumulation index and enrichment coefficient,that the heavy metals pollution followed the order of Cd > Cu > Zn > Ni > Pb > Cr. According to the potential ecological risk factor,Cd was identified as the key ecological risk factor and the result indicate that Baiyun Lake and Dongshan Lake met the extreme serious ecological risk,Liuhua Lake and Huadu Lake fall at the level of serious ecological risk. Multivariate statistical analysis indicate that the heavy metals in lakes of Guangzhou City were mainly derived from the runoff of city,and direct and indirect discharge of industrial and domestic sewage.

The impacts of crop planting change on agricultural productive efficiency and the environmental sustainability were evaluated by using emergy analysis method,elasticity approach and the planting data of Hubei province from 1978 to 2015. Results indicate that the agricultural productivity was relatively high and presented an environmental sustainability in Hubei province overall the period,whereas the environment load had been found increasing in recent years. The emergy investment ratio (EIR)and emergy yield and investment ratio (EYIR)varied in different regions of Hubei province. The EIR and EYIR were both higher in the most productive regions. Jianghan plain,compared to the rest regions of the province,associated with a highest environmental loading ratio (ELR). Therefore,for the Jianghan plain the emergy sustainability index (ESI)was lower with slow growth. The EIR and EYIR were lower in the east and west areas of the province associated with a lower ELR,therefore the ESI was higher and supported a fast growth. The crop planting area elasticities of ESI were negative and the absolute coefficient values were great for rice,cotton,and legume crops cross the province from 1978 to 2015. The elasticity coefficients for vegetables and fruit crops were fluctuated with the values changing from positive to negative,and back to positive. The overuse of fertilizer resulted in the increase on ELR. More attention should be paid to the agro-ecosystem to mitigate the environmental pressure and promote the sustainability of agriculture,such as reducing application level of fertilizer.

The vegetation cover and management factor (C)in the revised universal soil loss equation (RUSLE)model is used to indicate the effect of vegetation cover on soil erosion,and is one of the key parameters for evaluating soil erosion. The precise estimation and the spatial distribution characteristics of the long-term sequence of C factor at the regional scale are important for the prediction of dynamics of regional soil erosion. Therefore,timely and accurate grasping of the long-term sequence of C factor at the regional scale is very important for studying the dynamic relationship between soil erosion and vegetation. The remote sensing image in Nanjing City from 1988 to 2013 was selected and used. The quantification coupling model between leaf area index (LAI)and C factor was constructed based on BP neural network and the vegetation structure factor LAI inversed by remote sensing. The field measurement of C factor was obtained by ¹³⁷Cs isotope tracer technique,and the accuracies of the inversion models were verified. The results showed that: (1)The traditional vegetation coverage based on normalized difference vegetation index (NDVI)was generally larger than that based on LAI. The C value was generally smaller than the measured value,and the RMSE was 87.829%. While the C value calculated by LAI was close to the measured value,and the RMSE was 30.017%. Therefore,the C value calculated by LAI can reflect the actual vegetation structure information better than by NDVI. (2)The area with C value greater than 0.3 was mainly distributed in the urban areas with dense buildings,sparse vegetation and simple vegetation structure or even no vegetation cover. The area with C value less than 0.05 was mainly distributed in the hills and mountainous regions with dense vegetation structure. The distribution of C value in Nanjing City was closely related to vegetation cover and land use types. (3)Over the whole city where the C values were less than 0.05,during the period from 1988 to 2013,the area with strong resistance to soil erosion firstly decreased from 15.66% (1988)to 9.43% (before 2006)and then gradually increased to 12.07%. For the region where C values were greater than 0.3,the area with weaker resistance to soil erosion firstly slowly increased from 7.29% to 9.22% (2002),then it quickly increased to 12.31% (2002-2006)and then slowly decreased to 11.77%. Therefore,it is feasible to retrieve the long-term sequence C factor based on BP neural network and LAI proposed in this paper,which provides a new way for quantitative remote sensing monitoring of soil erosion on regional scale.

The changes of ¹³C content in ¹³C pulse-labeled Spartina alterniflora plants and root soil organic carbon were analyzed under different levels of nitrogen (N)and phosphorus (P). The effects of N and P addition levels on the distribution and fixation of photosynthetic carbon in S. alterniflora-soil system were studied. The results show that the abundance of ¹³C in each treatment group was significantly increased after four pulse marks. Except for the treatment of NP1,the abundance of ¹³C showed a decreasing trend in the order of stem,leaf,root,rhizosphere soil and soil,which was consistent with the control group (CK). The total amount of ¹³C fixed in each treatment group show a trend of continuous increase,but it was lower than that of the control group. The average fixed ¹³C amount of NP treatment was higher than that of N or P treatment alone. During the development of plants,the proportion of photosynthetic carbon in the aboveground gradually decreased while the proportion of underground gradually increased,and the accumulation of organic carbon ¹³C in soil was enhanced. With the development of plants,the differences in the distribution of ¹³C in each part of S. alterniflora-soil system became similar and tend to be consistent. In the N-added group,the allocation ratio of carbon in rhizosphere soil and soil increased with the increase of N addition level,indicating that N application could promote the transfer of photosynthetic carbon to soil. In the P-added group,the highest underground allocation ratio of photosynthetic carbon was observed in the medium level of P addition treatment (P2),which was conducive to the underground transfer of photosynthetic carbon. In the NP-added group,the aboveground distribution ratio was the highest at medium NP level (NP2),and the distribution ratio of rhizosphere soil and soil increased with the increase of NP addition. The addition levels of N and P and types of nutrients can change the distribution of photosynthetic carbon in S. alterniflora-soil system,indicating that eutrophication had significant ecological effects on the carbon cycle in salt marsh ecosystem.

Soil fauna play a key role in the material circulation and energy flow of wetland ecosystem. However,soil fauna populations are susceptible to environmental factors. Nanniwan wetland is a marsh wetland in the Loess Plateau of northern Shaanxi,which is seriously affected by human activities in China. Under the interference of human factors,debris flow degradation of different degrees has been formed in Nanniwan area,and wetland degradation has become an increasingly serious ecological problem in northern Shaanxi. At present,there are six typical habitats in this area (natural wetland,mildly degraded wetland,moderately degraded wetland,severely degraded wetland,cultivated wetland and farmland wetland). However,the changes of community structure and diversity of soil fauna in six habitats are still unclear. Three 50 cm×50 cm plots were randomly selected in each habitat to investigate the effects of wetland degradation on soil fauna communities in March,June,September and November 2016. A total of 3 285 soil animals were captured, which were divided into 4 phyla,10 categories and 26 orders. The dominant groups of soil fauna were echinococcus,striatum and springtail. The density and groups of soil animals decreased with the deepening of degradation. In severely degraded wetlands and cultivated lands,the density and diversity indexes of soil animals were significantly lower than those in other degradation stages (P<0.01). The difference of Sorenson similarity coefficient and Morisita-Horn similarity coefficient in different degradation stages indicate that degradation,reclamation and returning had significant influence on the composition of soil fauna community and dominant individuals in Nanniwan wetland. The seasonal dynamics of soil fauna community density and diversity are different in different degradation stages. The degradation of Nanniwan wetland will affect the seasonal stability of soil fauna community. The degradation of Nanniwan wetland also changed the spatial and temporal distribution of the dominant taxa of soil fauna. The regression analysis results of soil animal density and related soils factors show that soil animal density was positively correlated with soil organic matter and total nitrogen content,and negatively correlated with soil pH value. On the above basis,we can conclude that the degradation of Nanniwan wetland affects the spatial and temporal distribution and seasonal dynamics of the soil fauna community composition and diversity. Cultivation can reduce the density and diversity of soil animals,and the measures of returning farmland to forest can lead to seasonal changes of soil animal density.

Understanding the role of soil nitrogen migration is an important part of agricultural non-point source pollution research. Studies on the vertical distribution of soil nitrogen and the influence of different land use patterns are very helpful for the investigation of nitrogen migration. 38 undisturbed soil columns (1-m depth)from paddy fields,woodlands and tea gardens were collected from a typical subtropical hilly red soil region. Each soil column was divided into four layers (0-20,>20-30,>40-50 and >70-80 cm)and sampled at 5-cm intervals to determine ammonium,nitrate,total nitrogen and other soil properties. Additionally,the vertical distribution pattern of soil nitrogen in relation to different land uses was investigated. The results show that total soil nitrogen in the paddy fields had mean values of 2.44 (0-20 cm),1.49 (>20-30 cm),1.30 (>40-50 cm)and 1.20 (>70-80 cm),which were significantly higher (P<0.05)than in the woodlands and the tea gardens. There was no significant difference in ammonium among the various land usages. The surface layer (0-20 cm)nitrate content in the paddy fields was significantly higher (P<0.05)than in the tea gardens and the woodlands. Nitrate content in the subsurface layers from the tea gardens was significantly higher (P<0.05)than the paddy fields and the woodlands. It was also found that total soil nitrogen was closely related to nitrate content (r=0.64,P<0.01). Soil organic carbon,soil profile depth and bulk density were important factors affecting the vertical distribution of soil nitrogen. There was a significant positive correlation between soil nitrogen and organic carbon,and a significant negative correlation existed between soil nitrogen and bulk density or soil profile depth (P<0.05),which indicate that the soil nitrogen distribution is influenced by soil properties. The results of this study are helpful to the risk evaluations of water pollution caused by agricultural nitrogen fertilizer application in hilly red soil regions.

To provide a theoretical basis for reducing ammonia volatilization from paddy fields,the effects of different water management and nitrogen schemes on ammonia volatilization from paddy soil were studied. A field experiment was conducted to study the dynamics of ammonia volatilization by the closed airflow chamber method under a paddy ecosystem in the Jianghuai Hilly Region from June to September 2016. The results show that 52.92%-90.78% of total ammonia volatilization during the rice growth period occurred within the first 11 days after basal fertilization. A single basal application of slow-release urea combined with common urea reduced ammonia volatilization by 8.27%-14.22%. For conventional fertilization,ammonia volatilization under controlled irrigation decreased by 10.04% relative to that under conventional irrigation. A positive correlation was observed between ammonia volatilization and ammonium-nitrogen concentration in the surface water or 0-10 cm soil. The single basal application of slow-release urea combined with common urea under the water-saving irrigation treatment was identified to be a high-efficiency and environmental friendly model,referred to as the water-nitrogen application coupling management model.

The aim of this study is to investigate the adsorption characteristics of cadmium on goethite (G)and humic acid-coated goethite complexes (GH)under the application of phosphate by the isotherm and kinetic adsorption experiments. The effects of pH and ionic strength on cadmium adsorption were also determined. The results show that both the specific surface area and the isoelectric point of humic acid-coated goethite complexes were lower than those of goethite. However,the surface sites density of the complexes coated by humic acid was higher than that of goethite. The Langmuir equation and pseudo-second-order model were applied to describe the isotherm and kinetic adsorption of cadmium on goethite and humic acid-coated goethite complexes,respectively,and the better fitting effects were achieved. The presence of humic acid coated on goethite enhanced the maximum adsorption (X_m,q_e)and the adsorption affinity (K_L)of cadmium. With the increase of ionic strength,the reduction rate of cadmium adsorption on goethite was lower than that on complexes at pH 4.5,while the reduction rate of cadmium adsorption on complexes was lower than that on goethite at pH 6.5. The cadmium adsorption and its maximum theoretical adsorption on both goethite and complexes were increased at the presence of phosphate. The coexistence of phosphate improved the adsorption affinity,the average adsorption rate constant (k)and the initial adsorption rate (h)at pH 6.5. The inhibitive effects of increase of ionic strength on cadmium adsorption on goethite and humic acid-coated goethite complexes were also weakened by the presence of phosphate.

Heavy metal ions Cd²⁺ were adsorbed by potassium-permanganate-modified wheat straw. The modified wheat straw was characterized by scanning electron microscopy,zeta potential,and Fourier transform infrared spectroscopy. The effects of pH,adsorption time,solid-liquid ratio,and temperature of the solution and desorption on Cd²⁺ adsorption were also studied. Four different concentrations of potassium-permanganate-modified wheat straw were observed. Results show that,compared with the surfaces of other concentrations,the surface of 0.05 mol·L^-1 potassium-permanganate-modified wheat straw appeared smoother and had more negative charges. These outcomes were beneficial to improving the adsorption performance of Cd²⁺. Moreover,the adsorption reached equilibrium at 300 min and fitted the pseudo two-order kinetic equation. The best adsorption effect was obtained when the pH of the modified wheat straw was 6,and the solid-liquid ratio was 1:300. According to the Langmuir isothermal adsorption equation,the adsorbents prepared using the modified adsorbents of 0.05 mol·L^-1 had the largest adsorption capacity for Cd²⁺ (30.21 mg·g^-1)far larger than the optimum adsorption capacity of the unmodified wheat straw (5.7 mg·g^-1). The adsorbent has been found to have good stability for Cd²⁺ adsorption.

The problem faced by environmental pollution control of island exhibited similarities with those of the inland countryside,such as the backward infrastructure and sparse population. Meanwhile,the property of high moisture content of waste makes it difficult to be incinerated directly. Most remote islands rely on diesel-generator sets to satisfy power demands,which can produce abundant residual heat. Drying waste with the heat can also be a solution for waste incineration on the spot. In order to design the waste drying device,the experiments researching on drying characteristics of the island domestic garbage,were performed under the condition of available diesel generator flue gas temperature. Solid wastes from island and campus were included for comparison and Arrhenius equations which fitted to the waste drying process were obtained. According the results,following conclusions are summarized. The calorific value of solid waste increased significantly with the decrease of water content. Compared with campus solid waste which was treated by similar drying process,island solid wastes took longer time to dry. Under high temperature conditions,the drying process could be divided into adjustment stage and falling-rate stage,without the observation of constant-rate stage. To avoid self-ignition,temperature should be controlled below 220℃. The activation energy of island solid wastes is relatively higher, leading to more heat for drying.