Based on the Chinese surface climatologically daily dataset, the time and spatial variation of precipitation and relative humidity of 50 winters in the South China are studied by using the methods of climate tendency coefficient, climate tendency rate, and so on. Furthermore the spatial distribution of precipitation uniformity is analyzed by using Gini coefficient. The results show that the precipitation and relative humidity increased from northwest to southeast, the maximum center is located at the inland area near the south of Yangtze River, and the minimum center is located at plateau. The precipitation intensity increased overall, the region along the Yangtze River and part of Yunnan province increased obviously, the maximum climate tendency rate is about 1 mm/ day /10 a, and there is obvious mutation in 1979; precipitation increased slightly, but in the area of Yunnan, Guizhou and part of SichuanChongqin province, the precipitation amount showed a decreasing trend, about -3 mm/10 a, there is no obvious mutation; the precipitation days reduced significantly in the south of Yangtze River, Yunnan and Guizhou province, the minimum climate tendency rate in the southwest of Yunnan is about -10 days /10 a, mutation time is 1980; relative humidity showed a trend of increase or decrease locally, the relative humidity increased(decreased) slightly in the north(south) of the Yangtze River, the trend in south Yunnan is decreased significantly. There is positive relationship between relative humidity and precipitation, especially the relative coefficient with the precipitation amount and precipitation days is up to 0.784 and 0.753 respectively. The spatial pattern of Gini coefficient is similar to that of precipitation, however maximum (minimum) center of precipitation is corresponding to the center of minimum (maximum) of Gini coefficient, the range of maximum or minimum region has some variation in different periods and different months of winter. Generally speaking, most region of central and eastern South China in winter is precipitation homogeneous area, and the southwest plateau is uneven area.

Key words：South China; winter; precipitation; relative humidity

In this study, the concentrations of V, Cr, Co, Ni, Cu, Zn, As, Cd and Pb in 104 street dusts from Nanchang city in winter and summer were determined. Geoaccumulation index (Igeo), health risk model recommended by USEPA, and multivariate statistical methods (principal component analysis and correlation analysis) were applied to evaluate the pollution degree, calculate the noncarcinogenic risk (HI) and carcinogenic risk (CR) (for children and adult), and identify the possible source of heavy metal, respectively. The result showed that the concentrations of Cr, Ni, Cu, Zn, Cd and Pb in street dust of Nanchang were significantly higher than soil background values of Jiangxi Province, while concentrations of V, Co, and As were comparable to corresponding background values. Concentrations of V, Co, and As had not significant seasonal difference, but had high spatial heterogeneity. Cu concentration had significant difference both in seasonal and spatial distribution. The high level area of the other investigated metals mainly distributed in central Nanchang and old industrial area. The result from Igeo indicated that Cd, Cu, Zn, and Cr had higher pollution degree, while V, As, and Co had lower degree. The health risk from three exposures sequenced as handmouth ingestion>dermal contact> inhalation, and the child suffered the higher risk than the adult. The HQ and HI of all investigated metals were below one, except the HQ and HI of As and Cr exceed one in some sites. The Carcinogenic risk from metals in street dust were limited within the safe threshold range, and the sequence followed Cr > As > Co > Ni > Cd. There were various sources of metals in street dust from the Nanchang city, As, Co and V were mainly derived from rocks weathering, while the other metals came from the anthropogenic activities including the traffic and industry.

Key words：street dust; heavy metal; spatialtemporal distribution; health risk; Nanchang city

Based on timeseries remote sensing imagery (MODIS NDVI, Landsat) and meteorological observation data, this study analyzed spatiotemporal trends of vegetation coverage and their responses to climate change and human activities in the Danjiangkou Reservoir Region between 2000 and 2015 with the application of trend analyses, partial correlation analyses and transfer matrixes of land use. The results showed as follows: 1) There was an increasing trend of annual average vegetation coverage in the Danjiangkou Reservoir Region in the past 16 years, with a growth rate of 4.73%/10 a (p < 0.001). 2) 40.94% of the area increased significantly, which were mainly distributed in hilly lands and alluvial plains around the reservoir; 10.04% of the area showed significant decreasing results, which were primarily located in the northwest of Funiu Mountains and surrounding regions of builtup areas; 49.02% of the area had nonsignificant changes. 3) Vegetation coverage in the Danjiangkou Reservoir Region was not notably affected by climate change, but was greatly influenced by human activities. Shrubgrassland or farmland transformed into forestland was the main reason for the overall increasing trend of vegetation coverage in the reservoir region. Moreover, farmland converted into water body or builtup area was the important factor for the decreasing trend of vegetation coverage in local regions. These changes in land use were mainly driven by afforestation, project of returning farmland to forest, reservoir impounding and construction activities. 4) The implementation of ecological construction projects has played a positive role in the steady increase of vegetation coverage in the Danjiangkou Reservoir Region to a certain extent.

Key words：vegetation coverage; trend of change; land use; the Danjiangkou Reservoir Region

To understand the soil heavy metal pollutions nearby the Tonglvshan mine, Daye city(Hubei province, China), the soil samples and eight types of vegetables were analyzed with their Cd, Cu, Pb and As concentrations from seven sampling sites around the mine, the heavy metals’ biomagnifications and the potential risks to people’s health were also evaluated in this study. Heavy metals were analyzed by ICPMS, the biomagnification and health evaluation were performed by bioconcentration factor (BCF), Influence index of comprehensive quality (IICQ), and target hazard quotient (THQ). The results showed the soil samples have been seriously contaminated, the mean concentrations of Cd, Cu, Pb and As in soils recorded as 2.56 mg/kg, 363.23 mg/kg, 121.25 mg/kg and 35.96 mg/kg, respectively; these were 15.06, 11.83, 4.54 and 2.92 times of the provincial soil averaged backgrounds, respectively. Compared with the National Foods Contaminants Limits (GB27622012), the vegetables Cd, Cu and Pb concentrations were higher than the limits 40%, 6% and 2%, respectively, whereas the As concentrations fall within the National limit. The BCF values of soil and vegetables followed with the order of Cd > Cu > As > Pb, and the heavy metals BCF values in the leafy vegetables were all higher than the nonleafy vegetables. The IICQ of the soilvegetable system was calculated as 9.76, which accounted for critical heavy metals pollutions. People’s might be exposed to the As pollutions through the consumption of those polluted vegetables, as the THQ of As via vegetable consumption was higher than 1. The total heavy metals THQs for adult and child were 1.71 ~ 3.98 and 2.20 ~ 5.10, respectively. The people living around the Tonglvshan mine were suffering health risks through the heavy metal polluted vegetables.

Key words：Tonglvshan mine; vegetable; heavy metal; health risk

The riverbed and channel planform in the middle Yangtze River (Jinjiang reach) was significantly changed along with the four systematic cutoffs including two natural cutoffs (at Lianziwan and Shatanzi) and two artificial cutoffs (at Zhongzhouzi and Shangchewan) occurred during 1949-1979. Using the hydrological data and remote sensing images from 1955 to 2016, we calculated the erosion volume of new channels and deposition volume of old channels (i.e., oxbow lake), and analyzed the evolution process and the current status of the formed oxbow lakes. We found that the oxbow lakes were mainly influenced by local human activities. The increase of the channel gradient due to the four cutoffs causes adjustment of stream power along the channel and forces erosion of the channel bed in the long term and coarsening of bed material. The channel bed of the Jinjiang reach adjusts to its erosiondeposition equilibrium state until 1990s, with a slight deposition in the lower Jinjiang reach.

Key words：Middle Yangtze River; meandering channel; cutoff; erosion; stream power; oxbow lake

Located in the midlatitude subtropical region, the mountain peat bog in the Dajiuhu Basin of the Shennongjia area, Hubei abounds with climate change information. This information indicated by the profile of continuous peat deposition in the Dajuhu Basin is of great significance to reveal the climate change pattern in midlatitude China at different time scales. In this study, the Dajiuhu Basin peat was characterized with respect to its absorbance using the alkali extraction method, humification degree represented by E4/E6, and magnetic susceptibility. Combined with climatic proxies including E4/E6 and magnetic susceptibility, the chronosequence of the Dajiuhu Basin peat determined by the AMS14C dating technique was used to analyze the paleoclimate near the Dajiuhu Basin. The paleoclimate and precipitation are related to the magnetic susceptibility and E4/E6 in the same region. A higher magnetic susceptibility or a larger E4/E6 value (i.e., a lower humification degree) suggests a cold and dry climate and little precipitation. Upon the results, the climate evolution of the Dajiuhu Basin since the last deglaciation (18.7 ka BP) was reconstructed. A predominant cold and dry climate intercalated by warm and humid period was observed during 18.7-11.7 Ka BP, followed by a warm and humid climate and raised temperature in general during the Holocene (11.7-0 Ka BP). Specifically, the Early Holocene (11.7-9.3 Ka BP) was featured by a cold and dry climate (with occasional warm and humid periods), the Middle Holocene (9.3-3.5 Ka BP) warm and humid, and the Late Holocene (3.5-0 Ka BP) warm and dry.

Key words：peat; magnetic susceptibility;E4/E6; Dajiuhu basin; climate change

Aquatic ecosystem is the most important sources of greenhouse gases. However, the uncertainty in estimating the gas flux of water gas interface has not yet been paid attention to by using the linear regression (LR) model in the static floating box method (SFC).This study in Xiangxi Bay of Three Gorges reservoir, using closed static floating box  greenhouse gas analyzer continuous and realtime observation of the gas water interface of methane and carbon dioxide, and through software for fitting the monitoring data fitting. The comparison and analysis of the linear regression (LR), two regression (QR) and exponential regression (ER) fitting results of three kinds of models, the results show that it can better fit the static floating box gas concentration change with time nonlinear regression model, to get closer to the real gas water interface gas flux. This paper argues that the use of linear regression (LR) model to simulate the air interface of the gas flux of the obtained results are largely underestimated, the method of methane and carbon dioxide gas flux estimates averaged about 77% and 80% of the measured value. Moreover, in most cases, the effect of the exponential fit model is better than that of the two fit model, while the two regression model has no physical meaning in terms of the fitting coefficients, and is not applicable to the estimation of gas flux theoretically.

Key words：Static floating chamber; Gas flux estimation; Fitting model；Nonlinear fitting

Soil and grassland vegetation are important components for the grassland ecosystem, and they affect each other closely. The effect of grassland vegetation degradation on soil water holding capacity is a key problem for the research on grassland ecology, which is of great theoretical and practical importance to revealing the changes of water conservation function. In this study, the Tanggula Town of Golmud City in the headwaters area of Yangtze River was selected as the study area. The characteristics of soil water holding capacity in different grassland vegetation degradation stages were analyzed using soil sampling and lab analysis methods, and the effects of grassland vegetation degradation on soil water holding capacity were also discussed. Four important conclusions were obtained according to this research, listed as follows: (1) In the same grassland vegetation degradation stage, the changes of capillary water capacity, saturated water content and field water capacity depending on soil layers of different depths were similar. Moreover, in the same soil layer, the changes of the capillary water capacity, saturated water content and field water capacity depending on different grassland vegetation degradation stages also showed similar tendency. (2) In the same grassland vegetation degradation stage, the soil water holding capacity decreased as the increasing of soil layer depth in general. Especially in the nondegraded stage, the capillary water capacity, saturated water content and field water capacity in the soil layer of 10-20 cm depth decreased by 12.38%, 33.73% and 7.64% respectively, compared to those in the soil layer of 0-10 cm depth. (3) In the soil layer of the same depth, the capillary water capacity, saturated water content and field water capacity declined as the vegetation coverage degraded. Especially in the soil layer of 0-10 cm depth, the capillary water capacity, saturated water content and field water capacity in the slight degradation stage decreased by 41.52%, 59.95% and 27.03% respectively, compared to those in the nondegraded stage. (4) Soil water holding capacity significantly related to the soil bulk density, organic matter, total carbon, and total nitrogen. The characteristics of capillary water capacity, saturated water content and field water capacity in the different grassland vegetation degradation stages and soil layers might closely related to the changes of bulk density, organic matter, total carbon, total nitrogen and so on, which were induced by the landcover, biomass amount, distribution characteristics of plant roots on the earth surface. The theories, methods and technology system applied in this study can also provide experience for other headwater regions or similar research. These important conclusions could not only build a deep understanding for the relationship between grassland vegetation degradation and soil water holding capacity, but also provide the basis for the research of ecological environment and water resources in the headwaters area of Yangtze River.

Key words：soil water holding capacity; grassland vegetation degradation; headwaters area of Yangtze River; effect

Using the historical materials of 5 sites on drought and flood in the region of Poyang lake basin and the surrounding area from 1467 to 2016, combined with data from China recent five hundred years of drought and flood atlas and modern precipitation data, the drought and flood series had been reconstructed based on the correlation coefficient weighted method. Spatiotemporal variation of drought and flood series in the Poyang lake basin in recent 550 years were analyzed by means of Ensemble Empirical Mode Decomposition and Empirical Orthogonal Function. The results show (1) the changes of the IMF components in the Poyang lake basin are in line with the characteristics of the nonlinear changes of natural signals, and the main highfrequency change period is 2-3 a, 7-8 a; the middle and low frequency cycle is 22 a, 36 a; the low frequency cycle is 110 a, 220 a and so on. (2) The EOF decomposition of the spatial field of the drought and flood series shows that the cumulative variance contribution of the first four modes is 93.68% and the convergence effect is obvious. The first mode is the whole region has the same drought or flood state. The second and third modes represent the inconsistency of drought and flood in northsouth direction and eastwest direction. The fourth model represents the extreme precipitation type in South Jiangxi province. (3) The results of the power spectrum analysis of the time series of main spatial modes show that the change period of the spatial pattern of drought and flood is consistent with the EEMD decomposition of drought and flood series.

Key words：EEMD; EOF; drought and flood variations; spatiotemporal variation; the Poyang lake basin

Urban wetlands are decreasing and the wetlands are converted to construction land with the rapid development of urbanization. The possibility of urban waterlogging is increasing with the risk increasing across the process. South Lake wetlands in Wuhan is selected to analysis the process and drivers of urban wetland loss and the relationship between the loss and the waterlogging with RS and GIS technology, based on multitemporal satellite remote sensing data between 1988 and 2015. Research results show that: (1) the area of South Lake wetlands had fallen off from 1988 to 2015 and the total of the wetland reduced 1 563 ha. The rate of the loss was decreased obviously with certain fluctuation in the region, which could be divided into four phases: the processes of slow decrease (1988-1996), sharp decrease (1996-2004), slow decrease (2004-2010) and static (2010-2015), at the average loss amount of 35.3 ha, 135 ha, 30 ha and 5.4 ha each phase respectively. The loss started from the north of South Lake and the south of the area was to an end. (2) Residence was always responsible for the loss wetlands and about 52% loss areas were converted to residence land which had a total area about 803 ha.  (3) By combining datasets wetland loss and waterlogging from authoritative and reliable media data, it was found that 85.7% of the identified occurred waterlogging disaster points were located in the area used to be wetlands. The ability of wetlands to store water declines because of the low elevation and the increasing amount of impervious surface in the area used to be wetlands. And the loss area of wetland is more vulnerable to waterlogging and floods in higher rainfall days.

Key words：urban wetland; the loss of lake; waterlogging; South Lake