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Increasing population is generally responsible for the degraded river ecosystem. Using regression models and mathematical functions, the research quantitatively estimated the population and elevational gradient effects on river water quality during nine surveys from 2006 to 2008 in the Jinshui River basin of the South Qinling Mts., China. The total factor scores at 11 different sampling sites were calculated in factor analysis and first used as pollution index to represent the water quality levels. Population and elevational gradient both significantly linked with most water quality variables and pollution index in correlation analysis and explained 36.5–77.8 % of the total variances in regression analysis, indicating that human activities were gradually frequent with population growth and affected the input and output of pollutants in river water. On the basis of regression models and quadratic functions among population, elevational gradient, and pollution index, the population capacity of the river basin was estimated as 1815 people, and the threshold value of elevation was calculated as 1174 m. The results of multivariate linear models further confirmed that population and population distribution had direct influences on river water quality. This study will facilitate the ecosystem management for mountainous streams and provide quantitative models for understanding and mitigating human impacts on river system.

Dendroecological techniques were employed to explore the growth response of subalpine fir (Abies fargesii) to climatic conditions across its altitudinal range in both the north and south aspects in the Shennongjia Mountains, central China. Correlation function analyses indicated that temperatures in current summer were significantly negatively correlated with fir radial growth at the lower limits, while temperatures in previous autumn and in current spring showed significantly positive correlations with fir radial growth at the mid- and high-elevations in both aspects. Radial growth of the subalpine fir was significantly and positively influenced by precipitation in previous autumn and in current spring at the lower elevations and by precipitation in current spring at the mid-elevations, while precipitation had no significant effects on its radial growth at the upper elevations. Moving correlation functions showed that temperatures in early spring of the current year (i.e., February-April) had a relatively stable effect on tree growth over time at the mid- and upper-elevations in both aspects. Thus, the growth of the subalpine fir responded differently to climatic conditions along the altitudinal gradient, showing that the importance of temperatures for the fir radial growth increased while the importance of precipitation decreased with increasing altitude in both aspects in the Shennongjia Mountains, central China.

The upper Han River, with a drainage area of 95, 200 km2, has a dominant vegetated land use of forests and shrubs with a total coverage of 81.3%, and agricultural lands, mostly along the riverine network, account for 14% of the total basin area. In this study, water samples were collected in 42 sites during the time period of 2005–2006 in the river, and nitrate-nitrogen and ammonium-nitrogen were determined in situ. Consequently, multivariate statistics analyses were conducted to investigate the interactive influence of landscape setting and stream flow seasonality on nitrogen concentration in river waters. In the high flow period, nitrogen concentrations ( N H 4 + –N and N O 3 − –N) in stream water were significantly correlated with forest coverage and bare land at the catchment level, and with respect to the riparian zones of 100, 200, 500, 1000-m width they were only significantly correlated with bare land. In the low flow period, nitrogen concentrations were respectively correlated with vegetation and bare land regardless of varying scale landscape settings, and additionally N H 4 + –N was significantly related to agricultural land in riparian zones of 500 and 1000-m width. Nevertheless, nitrogen could be predicted using bare land in the high flow period and in the low flow period vegetation was also a critical variable in particular for N H 4 + –N. Generally, nitrogen was better predictable by land use in the high flow period rather than low flow period, and land use composition within an entire catchment rather than this in the riparian zone was a better predictor of nitrogen concentrations in rivers. Thus, the interaction between landscape setting and water flow seasonality played an important role in regulating nitrogen concentrations in the subtropical river.

Aims Age structure and regeneration dynamics have been used to infer population response to environmental events and reconstruct for est development history. The aim of this study was to characterize and examine the differences of the age structure and regeneration dynamics of subalpine fir (Abies fargesii) forest across the altitudinal range in the north and south aspects in the Shennongjia Mountains, central China. Methods Ten plots (20 × 20 m) at eac h altitudinal zone (i.e. the low elevation, the middle elevation and the high elevation) were established in both the north and south aspects of the Shennongjia Mountains, central China. Dendroecological techniques were applied to obtain information about ages of the trees in the plots. The population age structure was analyzed to investigate the regeneration dynamics across the altitudinal range.

With the filling of the Three Gorges Reservoir, original vegetation in the water level fluctuation zone (WLFZ) between the elevations of 145 and 175 m disappeared due to the reversal of submergence time (winter flooding) and prolonged inundation duration (nearly half a year). To better understand the relationships between the environmental factors and recovered plant communities for reconstructing floristically diverse riparian zone, we conducted a field survey in 11 sites in the WLFZ in June 2010, and vegetation composition, flooding characteristics, heavy metals, and soil major nutrients were determined. Consequently, the canonical correspondence analysis was used to investigate the relationships between plant species composition and flooding characteristics, heavy metal contamination, and soil nutrients. Results demonstrated that vegetation in the WLFZ was dominated by annuals, i.e., Echinochloa crusgalli and Bidens tripartita, and perennials including Cynodon dactylon, and plant species richness and diversity were negatively associated with flooding duration, heavy metal contamination, and nutrients including total phosphorus, available phosphorus, available potassium, and nitrate. Our results suggest that plant species, recovering mainly through soil seed bank and regeneration of remnant individuals, have been influenced by the combined effects of environmental factors.

Over recent decades, a large uncultivated area has been converted to woodland and shrubland plantations to protect and restore riparian ecosystems in the Danjiangkou Reservoir area, a water source area of China’s Middle Route of the South-to-North Water Transfer Project. Besides water quality, afforestation may alter soil organic carbon (SOC) dynamics and stock in terrestrial ecosystems, but its effects remain poorly quantified and understood. We investigated soil organic C and nitrogen (N) content, and δ 13C and δ 15N values of organic soil in plant root-spheres and open areas in an afforested, shrubland and adjacent cropped soil. Soil C and N recalcitrance indexes (RIC and RIN) were calculated as the ratio of unhydrolyzable C and N to total C and N. Afforestation significantly increased SOC levels in plant root-spheres with the largest accumulation of C in the afforested soil. Afforestation also increased belowground biomass. The C:N ratios in organic soil changed from low to high in the order the cropped, the shrubland and the afforested soil. The RIC in the afforested and shrubland were higher than that in cropped soil, but the RIN increased from the afforested to shrubland to cropped soil. The δ15N values of the organic soil was enriched from the afforested to shrubland to cropped soil, indicating an increased N loss from the cropped soil compared to afforested or shrubland soil. Changes in the δ13C ratio further revealed that the decay rate of C in the three land use types was the highest in the cropped soil. Afforestation increased the SOC stocks resulted from a combination of large C input from belowground and low C losses because of decreasing soil C decomposition. Shifts in vegetation due to land use change could alter both the quantity and quality of the soil C and thus, have potential effects on ecosystem function and recovery.

Changes in vegetation and soil properties because of agricultural abandonment may affect soil nitrogen (N) and associated processes. We investigated soil N (total N: TN, inorganic N: NH4–N and NO3–N) and denitrification potential in cropland, pine plantations and abandoned agricultural land along a secondary succession sequence (grasslandshrublandsecondary forest) in a headwater catchment in the Qinling Mountains, northwest China. The results show that the soil denitrification potential differed significantly among the five land-use types with the highest potential in the secondary forest, followed by grassland, shrubland, cropland and plantations. The denitrification potential of the 20- to 40-cm layer was significantly lower compared with the topsoil (0–20 cm) across all land-use types. TN, soil organic matter (SOM) and NH4–N increased significantly with stand age, whereas there was an opposite trend in soil pH. However, the denitrification potential did not relate to stand age in a linear manner. We conclude that changes in soil TN, SOM and pH during vegetation succession following agricultural abandonment are critical controls on the denitrification potential.

The optimum growth of soil crust-forming cyanobacterial species occurs between 21 and 30 °C. When the temperature decreases below -5 °C, the liquid water in the cyanobacterial cells may freeze. In the natural environment, the temperature gradually decreases from autumn to winter, and the diurnal temperatures fluctuate enormously. It was hypothesized that the physiology of cyanobacterial cells changes in later autumn to acclimatize the cells to the upcoming freezing temperatures. In the present study, an incubation experiment in growth chambers was designed to stimulate the responses of cyanobacterial cells to diurnal temperature variations before freezing in late autumn. The results showed that "light" cyanobacterial soil crusts are more tolerant to diurnal temperature fluctuations than "dark" cyanobacterial soil crusts. After the first diurnal temperature cycle between 24 and -4 °C, the malondialdehyde (MDA) contents increased and the photosynthetic activity decreased. The superoxide dismutase activity increased, more extracellular polysaccharides (EPS) were secreted and the ratios of the light-harvesting and light-screening pigments decreased. With increasing numbers of diurnal temperature cycles, the MDA contents and photosynthetic activity gradually returned to their initial levels. Our results suggest that there are at least three pathways by which crust-forming cyanobacteria acclimate to the diurnal temperature cycles in the late autumn in the Hopq Desert, Northwest China. These three pathways include increased secretion of EPS, regulation of the ratios of light-harvesting and light-screening pigments, and activation of the antioxidant system. The results also indicate that late autumn is a critical period for the protection and restoration of the cyanobacterial soil crusts in the Hopq Desert.

a b s t r a c t With the completion of the Three Gorges project, native vegetation in the water level fluctuation zone Q2 between the elevations of 145 m to175 m disappeared due to the inundation with a hydrological regime with flooding in winter instead of summer, a reversal of the natural one. We conducted a field experiment in the riparian ecosystem in the Three Gorges Reservoir to study nitrogen (N) dynamics under short-term revegetation and flooding during the period from 2008 to 2009. Soil chemical and physical characteris- tics, net mineralization potential rate (NMPR), net nitrification potential rate (NNPR), and denitrification potential rate (DPR) were determined in the laboratory. These results showed a significant decrease in inorganic N (NH4 + -N and NO3 − -N) following the short-term revegetation and flooding, which was prob- ably related to the interactions between surface flow, flooding, plant N uptake, and N transformation. Plants in conjunction with flooding increased the NMPR and NNPR, and increased the DPR only at the beginning of the revegetation and then decreased DPR after the flooding by regulating the concentration of soil organic carbon (SOC) and C:N ratios in soil, and decreasing the soil bulk density. Vegetation types affected N dynamics by changing SOC, soil N availability, and C:N ratios. The inorganic N, NMPR, and NNPR were higher in shrub soil than those in herb and tree soils due to higher SOC, whereas the DPR in tree soils was low compared shrub and herb soils because of lower C:N ratios together with the lower SOC. These results imply that soil inorganic N declined following the revegetation and flooding, and the revegetation in the riparian zone could potentially improve water quality. © 2011 Elsevier B.V. All rights reserved.

The Three Gorges Dam (TGD) is by far the world's largest hydroelectric scheme. Due to its unprecedented magnitude, the TGD has been controversial ever since it was proposed in the early 20th century and building commenced in 1993. Recent problems, including geological disasters (e.g., landslides) in the uplands and algal blooms in the aquatic environment since the reservoir's partial filling to 156 m in 2006, suggest that the environmental challenge has never been greater than now. The environmental deterioration might be further intensified when the reservoir reaches its final water level of 175 m. Solving the environmental challenges will be essential for the sustainable development of the Three Gorges Reservoir region (TGRR), and environmental sustainability in the TGRR is a high priority for the nation considering its critical location in the Yangtze Basin, which contributes 40% of China's GDP. This article reviews primary environmental assessments for biodiversity conservation, the water environment, water level fluctuation zone, and the uplands after the partial filling in the reservoir region. It also discusses the success of mitigation efforts to date. Although there are successes in mitigation particularly in conservation of endangered plants and fishes, it seems likely that environmental conditions in the TGRR could only get worse in the short term. Building a partnership among the TGD stakeholders, including local residents, governments, and international communities is necessary to meet the mounting environmental challenge in the TGRR and beyond.

Background Cuttings and seedlings of Jatropha curcas L. were exposed to different regimes of lead (Pb) stress as Pb (NO3)2 at 0 (CK), 0.5, 1, 2, 3, and 4 mM kg −1 soil. Objectives The effect of Pb treatment on the root length, tolerance index, photosynthetic pigments, photosynthetic activity, lipid peroxidation, and antioxidant enzyme was studied in a greenhouse pot experiment. Results The results showed that root lengths and tolerance index decreased with increase of Pb concentration, but tolerance index of cuttings was always lower than those of the seedlings. For cuttings, Pb treatment had a stimulating effect on chlorophyll content, carotenoid content, and superoxide dismutase (SOD) activity at low concentration and an inhibitory effect at higher concentration. For seedlings, SOD activity increased with increasing Pb concentration. In both seedlings and cuttings, Pb caused inhibition of leaf growth and photosynthesis, and induced the membrane damage which was more obvious in the cuttings. In comparison with the control, the dynamic tendency of catalase and perxidase activities in the leaves of Pb-stressed plants all ascended, and then declined. Discussion The increase in enzyme activities demonstrated that seedlings were more tolerant to Pb stress than cuttings. These results also indicate that the antioxidant system may play an important role in eliminating or alleviating the toxicity of Pb in J. curcas seedlings and cuttings. The accumulation of Pb increased in a concentration-dependent manner; however, its translocation from root to shoot was low. The cuttings accumulated significantly higher Pb in roots than seedlings.

Lakes play an important role in socioeconomic development and ecological balance in China, but their water quality has deteriorated considerably in recent decades. In this study, we investigated the spatial–temporal variations of eutrophication parameters (secchi depth, total nitrogen, total phosphorus, chemical oxygen demand, chlorophyll-a, trophic level index, and trophic state index) and their relationships with lake morphology, watershed land use, and socioeconomic factors in the Yunnan Plateau lakes. Results indicated that about 77.8% of lakes were eutrophic according to trophic state index. The plateau lakes showed spatial variations in water quality and could be classified into high-nutrient and low-nutrient groups. However, because watersheds were dominated by vegetation, all eutrophication parameters except chlorophyll-a showed no significant differences between the wet and dry seasons. Lake depth, water residence time, volume, and percentage of built-up land were significantly related to several eutrophication parameters. Agricultural land use and social–economic factors had no significant correlation with all eutrophication parameters. Stepwise regression analyses demonstrated that lake depth and water residence time accounted for 73.8% to 87.6% of the spatial variation of single water quality variables, respectively. Redundancy analyses indicated that lake morphology, watershed land use, and socioeconomic factors together explained 74.3% of the spatial variation in overall water quality. The results imply that water quality degradation in the plateau lakes may be mainly due to the domestic and industrial wastewaters. This study will improve our understanding of the determinants of lake water quality and help to design efficient strategies for controlling eutrophication in the plateau region.

Lake-water quality is highly dependent on the landscape characteristics in its respective watershed. In this study, we investigated the relationships between lake-water quality and landscape composition and configuration within the watershed in the Yangtze River basin of China. Water quality variables, including pH, electrical conductivity (EC), dissolved oxygen (DO), Secchi depth (SD), NO2−, NO3−, NH4+, TN, TP, chemical oxygen demand (CODMn), chlorophyll-a (Chl-a), and trophic state index (TSI), were collected from 16 lakes during the period of 2001–2003. Landscape composition (i.e. the percentage of vegetation, agriculture, water, urban, and bare land) and landscape configuration metrics, including number of patches (NP), patch density (PD), largest patch index (LPI), edge density (ED), mean patch area (MPA), mean shape index (MSI), contagion (CONTAG), patch cohesion index (COHESION), Shannon's diversity index (SHDI), and aggregation index (AI), were calculated for each lake's watershed. Results revealed that the percentage of agriculture was negatively related to NO2−, TN, TP, Chl-a concentrations, and TSI, while the percentage of urban was significantly correlated with EC, NH4+, and CODMn concentrations. Among landscape-level configuration metrics, only ED showed significant relationships with TN, TP concentrations, and TSI. However, at the class level, the PD, LPI, ED, and AI of agriculture and urban land uses were significantly correlated with two or more water quality variables. This study suggests that, for a given total area, large and clustered agricultural or urban patches in the watershed may have a greater impact on lake-water quality than small and scattered ones. Copyright © 2011 John Wiley & Sons, Ltd.

Water samples were collected for determination of dissolved trace metals in 56 sampling sites throughout the upper Han River, China. Multivariate statistical analyses including correlation analysis, stepwise multiple linear regression models, and principal component and factor analysis (PCA/FA) were employed to examine the land use influences on trace metals, and a receptor model of factor analysis-multiple linear regression (FA-MLR) was used for source identification/apportionment of anthropogenic heavy metals in the surface water of the River. Our results revealed that land use was an important factor in water metals in the snow melt flow period and land use in the riparian zone was not a better predictor of metals than land use away from the river. Urbanization in a watershed and vegetation along river networks could better explain metals, and agriculture, regardless of its relative location, however slightly explained metal variables in the upper Han River. FA-MLR analysis identified five source types of metals, and mining, fossil fuel combustion, and vehicle exhaust were the dominant pollutions in the surface waters. The results demonstrated great impacts of human activities on metal concentrations in the subtropical river of China.

Soil denitrification in reservoir shoreline wetlands is an important process for remov- ing excess inorganic nitrogen from upland runoff and controlling eutrophication in aquatic ecosystems. As yet, little is known about the influence of vegetation characteristics on the soil denitrification potential in reservoir shoreline wetlands, although vegetation can affect both denitrifying bacteria and soil properties. In this study, we measured the spatial variability of denitrification enzyme activity (DEA) using acetylene block method in shoreline wetlands of the Danjiangkou Reservoir, a water source of the South-to-North Water Transfer Project in China. Results indicated that DEA ranged from 0.001 to 2.449 μg N (N 2 O) g -1 h -1 , with a mean of 0.384 μg N (N 2 O) g -1 h -1 . DEA varied significantly among five representative plant communities and the highest DEA (0.248-2.449 μg N (N 2 O) g -1 h -1 ) was observed in the Polygonum hydropiper community. Plant biomass and vegetation cover were significantly and positively related to DEA and together explained 44.2% of the total variance. These results suggest that vegetation characteristics should also be considered in assessing soil denitrification capacity and restoring shoreline wetlands for nitrogen pollution removal in the Danjiangkou Reservoir after dam heightening.

Water quality in lakes is influenced by a large number of watershed and lake characteristics. In this study, we examined the relative effects of watershed land use and lake morphology on the trophic state of 19 lakes in the Yunnan plateau and lower Yangtze floodplain, the two most eutrophic regions in China. Trophic state parameters consisted of total nitrogen, total phosphorus, chemical oxygen demand, chlorophyll-a, Secchi depth, and trophic state index, while lake morphometric variables included area, maximum depth, mean depth, water residence time (WRT), volume, and length to width ratio. Percentages of forest, grassland, cropland, unused land, built-up land, and water body in each lake's watershed were extracted from a land use map interpreted from Landsat TM images. A t-test indicated that lower Yangtze floodplain lakes were shallower and had higher percentages of cropland and built-up land in watersheds than Yunnan plateau lakes. Pearson's correlation analysis indicated that both watershed land use and lake morphometric variables were significantly related to most of the trophic state parameters. However, stepwise regression analyses demonstrated that the trophic state of the lower Yangtze floodplain lakes was mainly controlled by the percentages of cropland and built-up land in watersheds, while that of Yunnan plateau lakes was mostly determined by the lake depth and WRT. These results suggest that the relative effects of watershed land use and lake morphology on lake trophic state are dependent on the lake's location. This study can provide some useful information in watershed land use management for controlling eutrophication in Chinese lakes.

A total of 40 water samples were collected from five sites in the Danjiangkou Reservoir, an important drinking water source in China. Over the period November 2004–June 2006, eight field surveys were conducted and water temperature, pH, EC, major ions (Na+, K+, Ca2+, Mg2+, Cl-, and ) and Si were monitored to determine their temporal and spatial patterns across the reservoir. The controlling factors were analysed using the stoichiometry of the water chemicals and multivariate statistics including a correlation matrix and analysis of variance. The results revealed that waters in the reservoir are sub-alkaline and have a low solute load, and most water variables exhibit notable spatial and temporal variations. The major ion chemistry of the reservoir was controlled by carbonate weathering (of limestone) with the dominant ions Ca2+ and contributing 63–81% and 73–81% to the major cation and anion budgets, respectively. Carbonate dissolution was produced by both sulfuric and carbonic acids; in particul...

Surface water samples were collected from 42 sampling sites throughout the upper Han River during the time period of 2005–2006. The concentrations of trace metals were determined using inductively coupled plasma-atomic emission spectrometry (ICP-AES) for the seasonal variability and preliminary risk assessment. The results demonstrated that concentrations of 11 heavy metals showed significant seasonality and most variables exhibited higher levels in the rainy season. Principal component analysis (PCA) and factor analysis (FA) revealed that variables governing water quality in one season may not be important in another season. Risk of metals on human health was then evaluated using Hazard Quotient (HQ) and carcinogenic risk, and indicated that As with HQ >1 and carcinogenic risk >10−4, was the most important pollutant leading to non-carcinogenic and carcinogenic concerns, in particular for children. The first five largest elements to chronic risks were As, Pb, V, Se and Sb, in the dry season, while they were As, V, Co, Pb and Sb in the rainy season. This assessment would help establish pollutant loading reduction goal and the total maximum daily loads, and consequently contribute to preserve public health in the Han River basin and develop water conservation strategy for the interbasin water transfer project. © 2010 Elsevier B.V. All rights reserved.

Rare earth elements (REEs) have been proved ideal tracers for soil erosion and aggregation. REE tracer method (REETM) used to study soil erosion, as a new technique, has been developed in recent 20 yr. It is able to quantitatively monitor the temporal and spatial variation of erosion intensity, compared with traditional approaches. The applications of REETM in studying of sediment differentiation law, erosion process evolution, determination of sediment sources and sedimentation investigations, and determination of prediction parameters, were reviewed. Some application limitations were summarized.

In order to determine the changes in the characteristics of the vegetation and soil following agricultural abandonment and compare the effects of different restoration approaches on ecosystem recovery, we studied the vegetation community and soil characteristics (nutrients, bulk density, water content and pH) of Pinus tabulaeformis plantations and abandoned croplands in different successional stages in the Foping National Nature Reserve, located in the Qinling Mountains, northwest China. The results indicated that natural vegetation and habitat could be restored via natural regeneration. These spontaneous restoration forests were characterized by high diversity, high soil fertility and rich unique species. The soil organic matter, total carbon, total nitrogen, available potassium, community cover, depth of litter, depth of humus and soil water content increased significantly with years after abandonment, while the total potassium, total phosphorus, available phosphorus, soil pH did not seem to change significantly with abandonment time. The soil mineral nitrogen (NH4 -N +N O3-N) tended to increase during the first 50 years after abandonment and then decreased. The pine plantations tended to show a low level of biodiversity in tree and herb layer, but the shrub layer (including sapling) composition and diversity were similar to secondary forests. Although the pine plantation showed lower soil fertility, they did not seem to result in the habitat-degradation.

Lake eutrophication is influenced by both anthropogenic and natural factors. Few studies have examined relationships between eutrophication parameters and natural factors at a large spatial scale. This study explored these relationships using data from 103 lakes across China. Eutrophication parameters including total nitrogen (TN), total phosphorus (TP), TN:TP ratio, chemical oxygen demand (CODMn), chlorophyll-a (Chl-a), Secchi depth (SD), and trophic state index (TSI) were collected for the period 2001–2005. Sixteen natural factors included three of geographic location, five of lake morphology, and eight of climate variables. Pearson correlation analysis showed that TP and TSI were negatively related to elevation, lake depth, and lake volume, and positively related to longitude. All eutrophication parameters, except for CODMn and Chl-a, showed no significant correlation with climate variables. Multiple regression analyses indicated that natural factors together accounted for 13–58% of the variance in eutrophication parameters. When the 103 study lakes were classified into different groups based on longitude and elevation, regression analyses demonstrated that natural factors explained more variance in TN, TP, CODMn, Chl-a, and TSI in western lakes than in eastern lakes. Lake depth, volume, elevation, and mean annual precipitation were the main predictors of eutrophication parameters for different lake groups. Although anthropogenic impacts such as point- and nonpoint-source pollution are considered as the main determinants of lake eutrophication, our results suggest that some natural factors that reflect lake buffer capacity to nutrient inputs can also play important roles in explaining the eutrophication status of Chinese lakes.

Age structure and regeneration dynamics of subalpine fir (Abies fargesii) forest were studied across the altitudinal range in both the north and south aspects of the Qinling Mountains, China. Ages of individual fir trees were determined based on the number of rings counted from cores and the number of years to reach coring height estimated using age–height regression. Fir age structure and regeneration dynamics were similar in both the north and south aspects. A unimodal population age structure was found at the low- and mid-elevations in both aspects, indicating that environmental factors might play an important role in shaping A. fargesii age structure and regeneration at those sites. There was a recruitment pulse during the time period 1830–1890 at each altitudinal site, but no stem recruitment occurred at the low- and mid-elevations in the last century, which might be attributed to the intensive cover of understory bamboo. Fir trees were, however, persistently recruited at the upper limits during the last 150 years, and the fir tree density at the upper limits was significantly higher than that at the lower limits in both aspects. The fir population at the upper limits showed a significant increase in recruitment and stem density relative to the fir population at the low- and mid-elevations in the last century. We propose that the differences in recruitment might promote variations in stand structure and regeneration dynamics of the subalpine fir forests along the altitudinal gradient in the Qinling Mountains, China.

Agricultural soils are considered to have great potential for carbon sequestration through land-use change. In this paper, we compiled data from the literatures and studied the change in soil organic carbon (SOC) following the ‘Grain-for-Green’ Programme (GGP, i.e., conversion from farmland to plantation, secondary forests and grasslands) in China. The results showed that SOC stocks accumulated at an average rate of 36·67 g m−2 y−1 in the top 20 cm with large variation. The current SOC storage could be estimated using the initial SOC stock and year since land use transformation (Adjusted R2 = 0·805, p = 0·000). After land use change, SOC stocks decreased during the initial 4–5 years, followed by an increase after above ground vegetation restoration. Annual average precipitation and initial SOC stocks had a significant effect (p 0·05). The ongoing ‘Grain-for-Green’ project might make significant contribution to China's carbon sequestration. Copyright © 2009 John Wiley & Sons, Ltd.

A total of 252 water samples were collected from 42 sites across the upper Han River basin during the time period from 2005-2006. Major ions (Cl(-), NO3(-), SO4(2-), HCO3(-), Na+, K+, Ca2+ and Mg2+), Si, water temperature, pH, EC and TDS were determined and consequently correlation matrix, analysis of variance, factor analysis and principal component analysis were performed in order to identify their seasonal variations and atmospheric inputs into river solutes. The results reveal that pH, EC, TDS, Cl(-), SO4(2-), HCO3(-), Ca2+ and Mg2+, K+ and Si generally tend to show the minimum compositions in months belong to the rainy season, while the dry season for NO3(-) and Na+. NO3(-), Mg2+ and Si have the maximum concentrations in months belong to the rainy season. By comparing the major ions relating to hydrological regime, NO3(-), contrary to other elements, has higher concentration in the rainy season. The overall water quality is non-polluted, while there are indications of enrichment of inorganic anions including NO3(-) causing water entrophication in the near future. The atmospheric inputs contribute to river solutes is limited with a mean inputs of approximate 1% in the basin. The understanding of the major ion dynamics would help water quality conservation in the basin for China's interbasin water transfer project.

In 2002, China launched the South-to-North Water Transfer Project after completing a 50-year feasibility study. By 2050, the three-route (i.e., East, Middle, and West) project will be capable of transferring 44.8 billion m3/year of water from the water rich Yangtze River to the arid north to alleviate water shortage and help secure a balanced social and economic development across the nation. However, diversion of such a large quantity of water could profoundly change the riverine environment of the upper Yellow River and the lower reach of the Han River, a tributary of the Yangtze River and the water supplying area of the project’s Middle Route, because of changes in the annual discharge. Secondary salinization seems inevitable in the water receiving areas of the North China Plain, and decrease in the discharge of the Yangtze River will result in seawater intrusion into the Yangtze Delta. This paper describes the project and discusses its environmental implications. Additionally, a long-term monitoring strategy under the umbrella of the Chinese Ecological Research Network is proposed for environmental monitoring.

Multivariate statistical techniques have been widely utilized to assess water quality and evaluate aquatic ecosystem health. In this study, cluster analysis, discriminant analysis, and factor analysis techniques are applied to analyze the physical and chemical variables in order to evaluate water quality of the Jinshui River, a water source area for an interbasin water transfer project of China. Cluster analysis classifies 12 sampling sites with 22 variables into three clusters reflecting the geo-setting and different pollution levels. Discriminant analysis confirms the three clusters with nine discriminant variables including water temperature, total dissolved solids, dissolved oxygen, pH, ammoniacal nitrogen, nitrate nitrogen, turbidity, bicarbonate, and potassium. Factor analysis extracts five varifactors explaining 90.01% of the total variance and representing chemical component, oxide-related process, natural weathering and decomposition processes, nutrient process, and physical processes, respectively. The study demonstrates the capacity of multivariate statistical techniques for water quality assessment and pollution factors/sources identification for sustainable watershed management.

A split-plot design was used to study the physiological responses of anti-oxidative enzymes and carbohydrate contents of bermudagrass to different durations (0, 3, 7, 15, 30, 60, 90, 120 and 150 days) and depths of submergence (0, 1, 5 and 15 m). The results suggest that submergence caused a higher production of malondialdehyde and more significant changes in the different submerged treatments. The activities of catalase (CAT), superoxide dismutase (SOD), peroxidase (POD), ascorbate peroxidase (APX) and glutathione reductase (GR) in roots increased with the increase of the durations and depths of submergence, implying an integrated pathway involving CAT, SOD, POD, GR and APX for protection against the detrimental effects of activated oxygen species under submergence. Total soluble carbohydrate and starch contents of shoots and roots decreased with the increase of the depth and duration of submergence, but remained at relatively high level at the end of the study, showing quiescence is one of the major strategies of bermudagrass under the stress of submergence. The results suggest that bermudagrass can endure long-term and deep submergence by balancing between the formation and detoxification of activated oxygen species, lowering metabolism and reserving high amounts of carbohydrate.

Vegetated riparian zones adjacent to rivers and streams, can greatly mitigate nutrients, sediment from surface through deposition, absorption and denitrification, yet, human activities primarily land use practices have dramatically reduced the capacity. In this study, 42 sampling sites were selected in the riverine network throughout the upper Han River basin (approximately 95,200 km(2)) of China. A total of 252 water samples were collected during the time period of 2005-2006 and analyzed for physico-chemical variables and major ions. Correlation analysis, principal components analysis and stepwise least squares multiple regression were used to determine the spatio-temporal variability of water quality variables and in particular their correlations with land use/land cover in the 100 m riparian zone along the stream network. The basin in general has a better water quality in the dry season than the rainy season, indicated by the primary pollutants including COD(Mn) and nitrogen. Major ion compositions display large spatial and seasonal differences and are significantly related to land use and land cover in the riparian zone, while riparian landscape could not explain most of the water quality variability in T, pH, turbidity, SPM and COD(Mn). The research could provide help develop sustainable land use practice of the riparian zone for water conservation in the basin.

The study focuses on the chemical and trace element compositions of the dissolved load in the upper Han River, the water source area of the Middle Route of China's South-to-North Water Transfer Project. Water samples were collected in the high flow period and analyzed for cations by Inductively Coupled Plasma Atomic Emission Spectrometer and anions by ionic chromatography respectively, in order to understand the contributions of anthropogenic activities and rock weathering to river solutes, as well as the associated CO2 consumption in the carbonate-dominated basin. The river waters have a mean TZ+ of 2674 μeq/l ranging from 1034.3 to 4611.6 μeq/l, which is significantly higher than that of the global river waters. Calcium and HCO3−, followed by Mg2+ and SO42−, dominate the chemical composition of major species in the basin. There are three major reservoirs (carbonates, silicates and agriculture/urban effluents) contributing to the dissolved load in the river. Chemical weathering rate is approximately 53.1 t/km2/yr with respective carbonate and silicate weathering rates of 47.5 t/km2/yr (19.8 mm/kyr) and 5.6 t/km2/yr (2.1 mm/kyr). The CO2 consumption is estimated to be 64.69 × 109 mol/yr and 9.69 × 109 mol/yr by carbonate and silicate weathering, respectively. The contribution of the anthropogenic inputs to the dissolved load is estimated to be 16.7%, demonstrating the strong impacts of human activities on water chemistry.

The upper Han River basin with an area of approximately 95,000 km2, is the water source area of the Middle Route of China’s South to North Water Transfer Project. Thus, water quality in the basin’s river network is of great importance. Nutrients including dissolved inorganic nitrogen (DIN), NO3 −-N, NH4 +-N, and dissolved phosphorus (DP) were analyzed in 41 sites during the period of 2005–2006. Cluster analysis (CA), analysis of variance (ANOVA) and general linear models (GLM) were performed to explore their spatio-temporal variations in the basin. The results revealed that the DIN, NO3 − -N and NH4 + -N increased over the 2 year study period, and their concentrations in the wet season was higher than those in the dry season. The seasonal variation in nitrogen was strongly associated with seasonal pattern of precipitation and there was a negative relationship between DP concentration and river flow. Cluster analysis indicated high nutrient contents in the urban and agricultural production areas. The research will help articulate water resource management strategy for the interbasin water transfer project. © 2008 Elsevier B.V. All rights reserved.

The three-route South-to-North Water Diversion Project (SNWDP), transferring water from the water-rich Yangtze River and its tributaries to the much drier area of North China for irrigation, industrial and domestic use, has been implemented in China since 2002. Thus, water quality in the Danjiangkou Reservoir, the water source area of the SNWDP's Middle Route, is of great concern. We investigate its water quality from 2004 to 2006 by monitoring some important physical (T, turbidity and SPM) and chemical (DO, pH, alkalinity, TDS, SpCond, ORP, CODMn and BOD) parameters and nutrient (nitrogen and phosphorus) contents. Consequently, their spatial and temporal patterns in the reservoir were examined. The results indicate that the water of the reservoir is of a Ca and HCO3 type, and the major pollutants are nitrogen and CODMn. Comparisons among the sampling sites show that water quality increases downstream, implying the self-purification capacity of the reservoir. The reservoir in general has better water quality in the dry season than in the wet season. Integrated basin management would be critical of the water quality in the Danjingkou Reservoir for the interbasin water transfer project.

The Danjiangkou Reservoir, constructed in 1970s, is the water source area of the middle route of China's interbasin South-to-North Water Transfer Project. To serve such purpose, the Danjiangkou Reservoir Dam will be increased from its present 162.0 m to 176.6 m, and its regular water level from 157 m to 170 m above mean sea level. Vegetation development in the new reservoir margins is therefore one of great environmental concerns. To explore the potential origin of species in the present reservoir margin vegetation, we investigated and quantified the composition in the soil seed banks and established vegetations of the reservoir margins and its upstream- and downstream-wetlands. In both existent vegetation and seed banks, most species and seedlings were found in upstream wetlands, followed by reservoir margins and downstream wetlands. Seedling density of downstream wetlands was reduced by 75–80% compared to upstream wetlands and reservoir margins. This suggests that presence of the dam reduced the diversity and abundance of downstream propagules. Sorensen's coefficient and the comparisons of rare species indicated that the seed bank composition of reservoir margins was evidently associated with upstream wetlands. It implies that hydrochorous transport of seeds from the upstream catchment is critical for plant colonization of the reservoir margins.

This study intends to disclose orographic effects on climate and climatic impacts on hydrological regimes in Qinling Mountains under global change background. We integrate a meteorological model (MM5 model, PSU/NCAR, 2005) and a hydrological model (SWAT model, 2005) to couple hydrological dynamic with climate change in Qinling Mountains. Models are calibrated and validated based on the simulation of different combined schemes. Following findings were achieved. Firstly, Qinling Mountains dominantly influence climate, and hydrological process in Weihe River and upper Hanjiang River. Results show that Qinling Mountains lead to a strong north–south gradient precipitation distribution over Qinling Mountains due to orographic effects, and it reduces precipitation from 10–25 mm (December) to 55–80 mm (August) in Weihe River basin, and adds 25–50 mm (December) or 65–112 mm (August) in upper Hanjiang River basin; evapotranspiration (ET) decrease of 21% in Weihe River (August) and increase 10.5% in upper Hanjiang River (July). The Qinling Mountains reduce water yields of 23.5% in Weihe River, and decrease of 11.3% in upper Hanjiang River. Secondly, climate change is responsible for the changes of coupling effects of rainfall, land use and cover, river flow and water resources. It shows that average temperature significantly increased, and precipitation substantially reduced which leads to hydrological process changed greatly from 1950 to 2005: temperature increased and precipitation decreased, climate became drier in the past two decades (1980–2005), high levels of precipitation exists in mid-1950, mid-1970, while other studied periods are in low level states. The inter-annual variation in water yield correlates with surface runoff with an R 2 value of 0.63 (Weihe River) and 0.87 (upper Hanjiang River). It shows that variation of annual precipitation was smaller than that of seasonal precipitation.

The upper Han River basin (approximately 95,200 km 2 ) is the water source area of China’s South-to-North Water Transfer Project. Over the period from 2005 to 2006, a total of 292 grab samples collected from 47 sites in the upper Han River were analyzed for major ions (Cl − , NO 3 - , SO 4 2 - , HCO 3 - , Na + , K + , Ca 2+ and Mg 2+ ), Si, T, pH, EC and TDS. Correlation matrix and principal component analysis were used to quantify the geochemical and anthropogenic processes and identify factors influencing the ionic concentrations. The results reveal that the waters are slightly alkaline with low ionic strength, and all ions show remarkable spatial variations. The lowest solute concentrations are observed in catchment with higher vegetation cover, with higher Cl − , NO 3 - and SO 4 2 - concentrations occur in catchments with industrial establishments. The major ion chemistry of the upper Han River basin is mainly controlled by rock weathering with HCO 3 - and Ca 2− dominating the major ion composition. The spatial variation in overall water quality as well as comparison with WHO and Chinese standards for drinking water indicates that the basin has high-water quality, yet it is possible that NO 3 - enrichment will occur in the near future. This research will help water conservation in the basin for the interbasin water transfer project.

A total of 42 sampling sites were selected in the riverine network of the upper Han River basin (approximately 95, 200 km2) of China. Over the time period of 2005–2006, 252 water samples were collected and analyzed for physico-chemical variables in order to investigate their spatio-temporal variability in particular the relationship with land use and land cover. Analysis of variance (ANOVA) indicated significant spatial variability in pH, EC, TDS, turbidity, SPM, ORP and nitrogen across the basin. Meanwhile, nitrogen, ORP, IMn and turbidity generally displayed higher values in the rainy season. Correlation analysis and regression analysis indicated that water temperature, IMn, and nitrogen were significantly related to vegetated coverage, and subwatersheds with higher vegetation cover had relative lower turbidity, SPM, IMn, nutrients and TDS. Bare lands had significant influence on nitrogen concentration in the riverine network, implying its large geologic sources in the basin. Percentage of urban area was the predictor for pH and DP, while agricultural land for SPM and IMn. The research could provide critical information in sustainable land use practice for water resource conservation for the basin.

Dendroecological techniques were used to investigate the stand dynamics and the disturbance history of the subalpine fir forest in the Qinling Mountains of Shaanxi Province, China. The results indicated that 68% of the fir trees experienced 1–2 release events for a total of 10–29 (an average of 15.8) years, and 1–2 suppression events for a total of 10–27 (an average of 13.4) years before they reached canopy. Large number of Abies fargesii and Betula albosinensis recruitment coincided temporally with larger increases in the ring-width index from the 1830s to 1880s, suggesting occurrence of a major stand-wide disturbance during this time period. Few seedlings and saplings were found in the forest, and there was a dramatic decline in recruitment after 1890, probably because of the intensive cover of understory umbrella bamboo (Fargesia spathacea). Radial growth analyses indicated frequent canopy opening resulting from small-scale disturbances in the forest. Thus, the subalpine fir forest experienced frequent small-scale disturbances and infrequent large-scale disturbances in its developmental history, and these disturbances coupled with the understory umbrella bamboo might have influenced tree growth and species recruitment.

ARTICLE I NFO An exotic grass Spartina alterniflora was intentionally introduced to Jiuduansha wetlands in Yangtze River estuary in 1997, and since then it had rapidly replaced native plant Scirpus mariqueter that used to dominate the estuarine salt marshes. We investigated consequences of S. alterniflora invasion to soil labile and recalcitrant C and N compared to the native S. mariqueter using soil fractionation and stable C and N isotopes. Results showed that S. alterniflora increased soil labile carbon (LC), recalcitrant carbon (RC), and soil recalcitrant nitrogen (RN) contents significantly (Pb0.05) in the upper soil layers (0-60 cm) compared to the S. mariqueter soil. Soil labile nitrogen (LN) in the S. alterniflora soil, however, remained lower than that in the S. mariqueter soil (Pb0.01), except for the surface soil layer (0-20 cm). The LC accounted for, on average, 36- 38% of soil organic matter (SOM) in both communities, while labile N accounted for 32% of SOM in S. alterniflora soil and 48% in S. mariqueter soil. The δ 13 C values in S. alterniflora soil showed that S. alterniflora contributed on average 8.6% and 3.3% to the LC and RC pools, respectively, within the 0-100-cm soil layer. The greatest labile C contribution derived from S. alterniflora was found at the 40-cm soil whereas the proportion of recalcitrant C originating from S. alterniflora showed a decreasing trend with soil depth. These changes appeared to be associated with vertical distributions of roots and rhizodeposition. We also found that the δ 15

The South-to-North Water Transfer (SNWT) Project of China is the largest of its kind ever implemented. Of its three routes (i.e., East, Middle and West), the middle one will transfer 14 billion m(3) of water annually from the Han River, a tributary of the Yangtze and the water supplying area, to Beijing by 2030. Thus water quality in the 95,000 km(2) upper Han River basin is of great concern. A watershed management initiative has been implemented in the basin, and the ultimate objectives are to quantify basin's ecosystem functioning and to develop an integrated management system with respect to water resources conservation. Specifically, the program includes five activities: characterization of riparian ecosystems, detection of land use and land cover change, quantification of nutrient cycling of representative ecosystems, determination of spatial and temporal variations of water quality, and finally development of a watershed management system for water conservation. This article provides the justifications of the watershed management initiative and the initial results are comprehended with respect to the water conservation in the Han River basin.

Concentrations of trace elements and heavy metals (Al, As, Ba, Cd, Co, Cr, Cu, Fe, Hg, Mn, Ni, Pb, Sb, Se, Sr, V and Zn) in the Danjiangkou Reservoir, the water source area of the Middle Route of China's interbasin South to North Water Transfer Project, were analyzed using an Inductively Coupled Plasma Atomic Emission Spectrometer (ICP-AES) and compared with the national and international standards for drinking water. The results indicated that concentrations of As, Pb, Sb and Se in the Reservoir exceeded the standards and they would pose health risk for residents in the region and the water receiving areas of the interbasin water transfer project. Spatial and temporal variability of the trace elements and heavy metals in the Reservoir implies their mixed sources of natural processing and anthropogenic activities in the upper drainage of the Reservoir. The research results would help develop water resource management and conservation strategy for the interbasin water transfer project.

Dendroecological techniques have been employed to investigate the relationship between subalpine fir (Abies fargesii) growth and climatic variability throughout its elevational range on both south and north aspects in the Qinling Mountain of Shaanxi Province, China. Correlation analyses indicate that early spring and summer temperatures are the principal factors limiting its growth in the low- and middle-elevation distributional areas. In the high-elevation areas, it is the summer precipitation that affects A. fargesii radial growth. The previous year August and November temperatures show positive correlation with the radial growth in the low- and middle-elevation distributional areas of the south aspect, and in the high-elevation areas, precipitation in previous November has significantly negative influences on the radial growth. The previous year's temperature and precipitation have no significant effects on the radial growth of the fir trees in the north aspect. Thus, the growth of the subalpine A. fargesii responds differently to climatic conditions along the elevational gradient and in different aspects.

A dendrochronological technique was used to investigate canopy recruitment of beech (Fagus engleriana Seem.) trees in western Hubei Province of Central China by identifying growth releases through gap formation. The results indicated that 83% and 17% of the canopy trees regenerate in gaps and the understory, respectively. Radial growth analyses demonstrated that there are three modes for beech regeneration and canopy recruitment: (1) gap origin without suppression; (2) gap origin with period(s) of suppression; and (3) understory origin. Multiple periods of release and suppression imply that beech regeneration and canopy recruitment are very sensitive to gap formation.

The ~350 km2 water level fluctuation zone (WLFZ) in the Three Gorges Reservoir (TGR) of China, situated at the intersection of terrestrial and aquatic ecosystems, experiences a great hydrological change with prolonged winter inundation. Soil samples were collected in 12 sites pre- (September 2008) and post submergence (June 2009) in the WLFZ and analyzed for soil nutrients. Self-organizing map (SOM) and statistical analysis including multi-way ANOVA, paired-T test, and stepwise least squares multiple regression were employed to determine the spatio-temporal variations of soil nutrients in relation to submergence, and their correlations with soil physical characteristics. Results showed significant spatial variability in nutrients along ~600 km long shoreline of the TGR before and after submergence. There were higher contents of organic matter, total nitrogen (TN), and nitrate (NO3-) in the lower reach and total phosphorus (TP) in the upper reach that were primarily due to the spatial variations in soil particle size composition and anthropogenic activities. Submergence enhanced soil available potassium (K), while significantly decreased soil N, possibly due to the alterations of soil particle size composition and increase in soil pH. In addition, SOM analysis determined important roles of soil pH value, bulk density, soil particle size (i.e., silt and sand) and nutrients (TP, TK, and AK) on the spatial and temporal variations in soil quality. Our results suggest that urban sewage and agricultural runoffs are primary pollutants that affect soil nutrients in the WLFZ of TGR.

This paper examines the vulnerability of the Congo Basin's forests through a GIS platform, taking into consideration the variables of population growth, road density, logging concession, and forest fragmentation. The assessment indicates that the forests will continue to shrink towards the interior over the next 50 years. Current contiguous forests will fragment into three large blocks, including one on the west side of the Congo River and two in the Democratic Republic of Congo, while a large number of small forest patches will retain in the periphery of the large blocks. The study shows that integrated GIS assessment of the driving forces of tropical deforestation can shed light on the future forest distribution and provide a tool to address the broader implications of social and economic development for tropical deforestation.

This paper presents a semi-automatic procedure that integrates thresholding, region growing, and edge detection techniques for feature extraction in remotely sensed imagery. An interface has been developed to provide an interactive platform of the procedure. Thresholding technique is employed to sample object of interest. Estimated properties (i.e., mean and variance) of the sample are applied for feature extraction using region growing. Since the derived object is subject to the sample and initial conditions, edge detection is incorporated to calibrate initial parameters by examining how the derived object matches the local edges inherent in the imagery. The program is loosely linked to PCI (PCI Geomatics, Richmond Hill, Ontario, Canada), a widely distributed image processing software. We demonstrate applications of this procedure by deriving burned scars using SPOT VGT and NOAA AVHRR imagery.

Information of fine-root biomass and production is critical for quantifying the productivity and carbon cycle of forest ecosystems, and yet our ability to obtain this information especially at a large spatial scale (e.g., regional to global) is extremely limited. Several studies attempted to relate fine-root biomass and production with various aboveground variables that can be measured more easily so that fine-root biomass and production could be estimated at a large spatial scale, but found the correlations were generally weak or non-existed at the stand level. In this study, we tested a new approach: instead of using the conventional way of analysing fine-root biomass at the stand level, we analysed fine-root data at the tree level. Fine-root biomass of overstory trees in stand was first separated from that of understory and standardized to a common fine-root definition of < 2 mm or < 5 mm diameter. Afterwards, we calculated fine-root biomass per tree for a ‘representative’ tree size of mean basal area for each stand. Statistically significant correlations between the fine-root biomass per tree and the diameter at the ground surface were found for all four boreal and cool temperate spruce, pine, fir and broadleaf forest types, and so allometric equations were developed for each group using a total of n = 212 measurements. The stand-level fine-root biomass of trees estimated using the allometric equations agrees well with the measurements, with r2 values of 0.64 and 0.57 (n = 171), respectively, for fine-roots < 2 mmand < 5 mm diameter. This study further estimated fine-root production as the product of fine-root turnover rate and fine-root biomass, and determined the turnover rate as a function of fine-root biomass, stand age, and mean annual temperature. The estimates of tree fine-root production agree well with reported values, with r2 value of 0.53 for < 2 mm and 0.54 for < 5 mm diameter (n = 162) at the stand level.

Stand age distribution in boreal forests reflects past disturbances, which is a major determinant of the carbon strength (sink or source). We used mapped and dated fire scars as a reference and developed a remote sensing algorithm for mapping boreal forest stand age distribution that accounts for other stand-replacing disturbances such as harvesting. Considering its strong discriminatory capacity on vegetation type and stand age, a short-wave vegetation index (SWVI) (Remote Sensing of Environment 82 (2002) 95), calculated from the SPOT VEGETATION (VGT) near-infrared and short-wave infrared bands, was utilized to quantify forest regeneration following fire. Stand age of a pixel was then determined by its SWVI value in comparison with the known ones from the dated fire scars. A change indicator (Latifovic, R. (2001). VGT and AVHRR Manager User manual. Canada Centre for Remote Sensing, Natural Resources Canada. Ottawa, Ontario, Canada), which considered interannual changes in the Normalized Difference Vegetation Index (NDVI) from sequential NOAA Advanced Very-High Resolution Radiometer (AVHRR) imagery (1993–1998), was employed to differentiate areas with lower SWVI values resulting from biophysical factors other than disturbances. We evaluated the stand age distribution product using Landsat TM imagery and discussed the limits and constraints of the remote sensing approach of deriving stand age distribution in the boreal forest region.

Research on shifting cultivation in the tropics has focused primarily on the issues of agricultural productivity and soil degradation. Few have attempted to quantify its impact on forest losses and the carbon cycle in the context of the global change debate. A simulation, which incorporated historic and projected rural population growth, was conducted to investigate the impacts of shifting cultivation on deforestation and the carbon stocks of the humid tropical forests of central Africa. The study demonstrated that in 1950, the central African forest region subjected to shifting cultivation was composed of 92% forest (including primary and secondary forests) and that in 1990 the forest cover had been reduced to 80% of the total simulated land area. The results of the simulation showed that with the current level of technology and consumptive habitats, shifting cultivation under projected rates of rural population growth would increase the annual rate of deforestation to 1.3%, converting 94% of the land area into cropland, fallow and secondary forests by 2050. At that time, only 40% of the potential above-ground biomass carbon (i.e., assuming all the simulated area is occupied by dense forests) will remain, compared to 85 and 74% in 1950 and 1990, respectively. The simulation suggests that there is a need for alternatives to shifting cultivation such as integration of cultivation intensification, fallow management and agroforestry if population pressure on the tropical forests of central Africa is to be alleviated. This preliminary regional study shows that modeling could provide an important tool to explore alternative scenarios of land use and to assist decision makers with forest management.

Controversy surrounds the green credentials of hydroelectricity because of the potentially large emission of greenhouse gases (GHG) from associated reservoirs. However, limited and patchy data particularly for China is constraining the current global assessment of GHG releases from hydroelectric reservoirs. This study provides the first evaluation of the CO2 and CH4 emissions from China’s hydroelectric reservoirs by considering the reservoir water surface and drawdown areas, and downstream sources (including spillways and turbines, as well as river downstream). The total emission of 29.6 Tg CO2/year and 0.47 Tg CH4/year from hydroelectric reservoirs in China, expressed as CO2 equivalents (eq), corresponds to 45.6 Tg CO2eq/year, which is 2-fold higher than the current GHG emission (ca. 23 Tg CO2eq/year) from global temperate hydropower reservoirs. China’s average emission of 70 g CO2eq/kWh from hydropower amounts to 7 % of the emissions from coal-fired plant alternatives. China’s hydroelectric reservoirs thus currently mitigate GHG emission when compared to the main alternative source of electricity with potentially far great reductions in GHG emissions and benefits possible through relatively minor changes to reservoir management and design. On average, the sum of drawdown and downstream emission including river reaches below dams and turbines, which is overlooked by most studies, represents the equivalent of 42 % of the CO2 and 92 % of CH4 that emit from hydroelectric reservoirs in China. Main drivers on GHG emission rates are summarized and highlight that water depth and stratification control CH4 flux, and CO2 flux shows significant negative relationships with pH, DO, and Chl-a. Based on our finding, a substantial revision of the global carbon emissions from hydroelectric reservoirs is warranted.

Joint Implementation under the Climate Change Convention and Clean Development Mechanism of the Kyoto Protocol require a scientific understanding of current carbon stocks, fluxes, and sequestration potential, especially in tropical ecosystems where there are large carbon reservoirs, significant carbon emissions, and large land areas available for reforestation. Central Africa contains 10% of the world's remaining tropical moist forests and has received little attention in carbon studies. In 1980, above-ground carbon stocks in the central African ecosystem were 28.92 Pg and were reduced to 24.79 Pg by 1990. Improved forest management aimed at increasing biomass density could sequester 18.32 Pg of carbon, and over 500,000 km2 formerly forested land will be available by 2050 for reforestation with a capacity to offset 10 Pg carbon. Understanding the spatial distribution of biomass carbon and sequestration potential will be essential for carbon trading initiatives through Joint Implementation and Clean Development Mechanism.