This paper presents the results of bias corrections of Chinese standard precipitation gauge (CSPG) measurements for wind-induced undercatch, trace amount of precipitation and wetting loss. Long-term daily data of precipitation, temperature, and wind speed during 1951-2004 at 726 meteorological stations in China were used for this analysis. It is found that wind-induced gauge undercatch is the greatest error in most regions, and wetting loss and trace amount of precipitation are important in the low precipitation regions in Northwest China. Monthly correction factors (corrected/measured precipitation) differ by location and by type of precipitation. Considerable inter-annual variation of the corrections exists in China due to the fluctuations of wind speed and frequency of precipitation. More importantly, annual precipitation has been increased by 8 to 740 mm with an overall mean of 125 mm at the 726 stations over China due to the bias corrections for the study period. This corresponds to 5% -72% increases (overall mean of 18% at the 726 stations over China) in gauge-measured yearly total precipitation over China. This important finding clearly suggests that annual precipitation in China is much higher than previously reported. The results of this study will be useful to hydrological and climatic studies in China.
Annual distribution characteristic of river sediment concentration is closely related to climate change and anthropogenic activities and directly affected by the process of hydraulic resource development in the Lancang-Mekong River basin. Using monthly suspended sediment concentrations in 1987-2003 at the three hydrological stations, Jiuzhou, Yunjinghong and Chiang Saen stations, on the mainstream of Lancang-Mekong River, the uneven distributions coefficient, the concentrated rate and period, and the range of variation of annual distribution characteristics of sediment concentrations at the three stations were studied and then the responses of these characteristics to the progress of upstream dam constructions were analyzed. The research results show that: (1) Annual distribution of sediment concentration at Jiuzhou hydrological station agrees with the variation trend of local climate changes, its uneven distribution coefficients (AUDC) increased at the studied period and maintained the characteristics of natural river; AUDCs at Yunjinghong and Chiang Saen stations seemed to be affected by anthropological activities such as dam constructions rather than climate changes, however, sediments of two downstream stations responded differently to the dam constructions. AUDC at Yunjinghong station decreased from the periods of 1987-1992 to 1993-1996, then abruptly increased during 1997-2003; while AUDC at Chiang Saen took on a trend of moderate decreasing in the whole period. (2) Rates and distribution periods of sediment concentrations at Jiuzhou station almost kept stable during the studied period; but those at Yunjinghong and Chiang Saen changed evidently, their distribution periods delayed asynchronously during the dam construction processes (1987-1992, 1997-2003), in the period of Manwan dam construction, distribution periods at Yunjinghong station delayed 5-6 days, while Chiang Saen delayed almost half a month, and in the Dachaoshan dam construction, delayed period at Yunjinghong station was longer than that at Chiang Saen. (3) Relative and absolute ranges of sediment variations at Jiuzhou station both increased against the time phases; those at Yunjinghong decreased, while relative ranges of sediment variation at Chiang Saen decreased in the earlier years then increased later, but absolute range was decreasing all the time. Different responses of annual distributions of sediment concentration at three hydrological stations to dam constructions indicate that their driving factors of sediment variation are absolutely different. These discoveries of annual distribution characteristics of sediment concentrations present new scientific evidences for assessing the impacts of dam constructions on upstream and downstream sediment change as well as its transboundary effects.
The concentrations of heavy metals Ba, Pb, Cu, Zn and Co in snow pit collected in September, 2005 from the accumulation area of the East Ronbuk Glacier (a.s.l. 6523 m), which lies on the northern slope of Mt Qomolangma, were determined by inductively coupled plasma mass spectrometry (ICP-MS), concentrations (pg/ml) of heavy metals vary from Ba2-227, Co2.8-15.7, Cu10-120, Zn29-4948, and Pb14-142, respectively. And δ18O determined by MAT-252, the time period of the snow pit spanning from autumn 2005 to summer 2004. Seasonal variations of the concentrations and δ18O are observed, of which Pb, Cu, Zn and Co are much lower in summer monsoon season than that in non summer monsoon season, suggesting that different sources of heavy metals contributed to the site. EFc (crustal enrichment factors) is Co 3.6, Cu 27, Pb 33 and Zn 180, respectively. Higher EFc values of Pb, Cu and Zn suggest that Pb, Cu especially Zn mainly contributed by anthropogenic sources.
Based on historical documents, modern survey and statistics, as well as the result of predecessor studies, the trend and main process of forest dynamics are recognized. The forest area and forest coverage rates for each province of China from 1700 to 1949 are estimated backward by every 50 years. Linking the result with modern National Forest Inventory data, the spatial-temporal dynamics of Chinese forest in recent 300 years (A.D.1700-1998) is quantitatively analyzed. The study shows that in recent 300 years, the forest area in current territory of China has declined 0.95 ×108 ha (or 9.2 percentage points of coverage rate) in total, with a trend of decrease and recovery. Before the 1960s, there was a trend of accelerated descending. The forest area was reduced 1.66×108 ha (or 17 percentage points of coverage rate) in 260 years. While after the 1960s, there has been a rapid increase. The forest area increased by 0.7×108 ha (or 8 percentage points of coverage rate) in 40 years. The study also shows that there is a significant spatial difference in the dynamics of forest. The amplitudes of increasing and decreasing in western China are both smaller than the ones in eastern China. During the rapid declining period 1700-1949, the most decrease appeared in the Northeast, the Southwest and the Southeast, where the coverage rate in most provinces dropped over 20 percentage points. In Heilongjiang Province, the coverage rate dropped 50 points. In Jilin Province, it dropped 36 points. In Sichuan Province and Chongqing Municipality, it dropped 42 points. In Yunnan Province, it dropped 35 points. During the recovery period 1949-1998, the western provinces, municipality and autonomous regions, including Ningxia, Gansu, Inner Mongolia, Sichuan-Chongqing, Yunnan, Tibet, Xinjiang and Qinghai, etc., the increase rates of the coverage are all below 5 percentage points, while the eastern provinces, municipality and autonomous regions (except Heilongjiang, Hubei and Jiangsu-Shanghai) have achieved an increase over 5 percentage points, among which the Guangdong-Hainan, Guangxi, Anhui, Beijing-Tianjin-Hebei, Shandong, Henan, Zhejiang and Fujian have an increase over 10 points.
Phenological observation data of plant communities from 1982 to 1996 at 5 sites and a method for phenological cumulative frequency modeling were used to determine the beginning dates of local phenological seasons and their corresponding threshold values of normalized difference vegetation index (NDVI) in each year. Then, a year-type cluster analysis of NDVI profiles at each phenological station during 1982 to 1999 and a spatial cluster analysis of NDVI profiles for all of the pixels within the study area year by year were employed to fulfill a spatial-temporal extrapolation of vegetation phenological seasons. Consequently, we obtained spatial-temporal patterns of the beginning date of vegetation phenological seasons and the length of the vegetation growing season in the deciduous broad-leaved forest area of warm-temperate eastern China from 1982 to 1999. The results show that (1) the annual mean beginning dates of vegetation phenological seasons and the mean lengths of the vegetation growing season indicate changes of a spatial pattern mainly following latitude and altitude; (2) the beginning dates of the phenological spring dominate a significantly advanced trend over the entire area during 1982 to 1999, especially in North China Plain, whereas the beginning dates of the phenological summer, autumn and winter dominate a significantly delayed trend, also mainly in North China Plain, which causes a significant lengthening of the vegetation growing season in North China Plain; (3) linear trends of the beginning dates of vegetation phenological seasons are consistent with linear trends of seasonal air temperatures in North China; (4) the vegetation growing season lengthening revealed by the current study is consistent with the phenological growing season lengthening of the individual tree species in Europe, and the satellite-derived growing season lengthening in Eurasia and temperate China.
There has been an increasing use of predictive spatial distribution of main communities or dominant species at the regional scale for ecological restoration planning, biodiversity conservation planning and regional management decisions on the Loess Plateau. Understanding the spatial distribution of main communities at the regional scale is also essential in assessing the impacts of environmental change or human impacts on vegetation distribution. Based on the investigation of steppe cover that correlates with its habitat, this study focused on the prediction of steppe distribution in the Zulihe River watershed of the west-central Loess Plateau. First, we investigated the cover of steppe of 365 samples. Secondly, important variables (annual mean precipitation and annual mean temperature) that affect vegetation distribution were spatialized as functions of elevation and horizontal coordinates via a GIS. Thirdly, the niche spaces of steppe were determined by incorporating the spatially-distributed main variables with the steppe cover that came from field investigation and remote sensing data (Landsat TM image). The niche spaces defined then were extrapolated over the study area. Comparing the distribution of predicted steppe with its present distribution, we found that the natural vegetation in the region has been destroyed and disturbed by human activities. As a result, soil erosion has been aggravated. The ecological conditions in the study area have been progressively degraded by human-accelerated soil erosion. The object of the study is to provide important baseline for ecological restoration in the Zulihe River watershed.
Quantitative analysis was performed on filling and scouring process for the river reach between Makou and Tianjiazhen, the middle Yangtze River with the help of GIS and DEM technology. The research results indicate that the river reach between Makou and Tianjiazhen was dominated by the scouring process, and the magnitude of scouring is increasing over time. The intensity of scouring process is more in the deep and narrower river reach than shallower and wider ones. The river reach in the Makou and Tianjiazhen river knot is in frequent scouring and filling process, however the river reach upper to the Makou and lower to the Tianjiazhen river knot is in moderate scouring and filling process. The river reach just upstream or downstream to the river knot (e.g. Makou and Tianjiazhen river knot in this research) is dominated by filling process and the river reach in the river knot is dominated by scouring process. Research results indicate no changes happen in the boundary of the river but the scouring and the filling magnitude in specific river channel is strong. The filling and scouring process of the study river reach is greatly impacted by the sediments and water from the upstream of the study river reach. The construction of the Three Gorges Dam just upstream to Yichang will cause further decrease of the release of sediment load to the middle and the lower Yangtze River basin, which will further intensify the scouring process of the river channel in the study river reach.
Soil organic matter (SOM) turnover was studied for the Chongmingdongtan Salt Marsh in the Yangtze River Estuary, based on the analyses of stable carbon isotope (δ13C), grain sizes and contents of particulate organic carbon (POC), total nitrogen (TN) and inorganic carbon (TIC) for three cores excavated from high marsh, middle marsh and bare flat. Results indicated that correlations between soil POC contents and δ13C values of the salt marsh cores were similar to those of the upper soil layers of mountainous soil profiles with different altitudes. SOM of salt marsh was younger than 100 years, and originated mainly from materials of soil erosion in the catchment basin of the Yangtze River. Diagrams of TN-C/N, POC-TIC and POC-δ13C for the cores indicated that turnover degree of SOM from the salt marsh was generally low, and tendencies regarding SOM turnover were clear from bare flat to high marsh. Bare flat showed characteristics of original sediments, with minor SOM turnover. The turnover of SOM was discernable in the high marsh and middle marsh, and the mixing degrees of SOM compartments with different turnover rates increased with evolution of the muddy flat. The exclusive structure of muddy layer and sandy layer originated from dynamic depositional processes on tidal flat made great difficulties for vertical migration of dissolved materials, and SOM turnover was then constrained.
The analysis results of 58 surface sediment samples collected in February 2003 showed that the median diameter of surface sediment (D50) was decreased gradually from Jiangyin to the mouth of the Yangtze River Estuary, and the value decreased from 217.8 μm of Jiangyin to 12.1 μm of the mouth of South Passage. In Turbidity Maximum, the coarsest surface sediment was in North Channel, and the average median diameter was 126.2 μm. The coarser surface sediment was in North Passage, and the average median diameter was 48.4 μm. The finest surface sediment was in South Passage, and the average median diameter was 14.2 μm. While in the mouth of the estuary, the coarsest surface sediment was in North Passage, then in North Channel, and the finest surface sediment was in South Passage. The median diameter of the mouth of North Passage was 22.4 μm, and that of North Channel 16.5 μm, and South Passage 12.1 μm. The sorting of surface sediment was mainly moderately sorted to very poorly sorted, and the greater the median diameter, the smaller the sorting coefficient. The skewness was mainly nearly symmetrical to very positive. The kurtosis was mesokurtic to extremely leptokurtic. The composition of surface sediment in upper Hengsha island was mainly sand, while in the mouth of the estuary was mainly clayey silt. In Turbidity Maximum, it was much more complex and variational. There was positive relationship between the D50 of surface sediment and the ebb tidal duration, value of Ve/Vf and residual current speed in channel of the Yangtze River Estuary, and the ebb current condition was the main dynamic factor to determine D50.
