A 150-year isotopic record of lead deposition in Yancheng coastal wetland,China

Radioactive markers are useful in dating lead(Pb) deposition patterns from industrialization in sedimentary archives. As a well-known natural reserve in the world, Yancheng coastal wetland in Jiangsu Province is one of areas most sensitive to global sea level change and is located in the most developed and polluted region of China. Two cores were collected in Yancheng wetland in October 2013 and dated using ~(210)Pb and ~(137)Cs radiometric techniques. Sediments in both cores were sectioned into depth bands and examined systematically for dry bulk density, water content, magnetic susceptibility and grain-size. Multiple elements including Pb were also measured using inductively coupled plasma systems. Unsupported ~(210)Pb activities decreased with depth in both of the two cores, and ~(210)Pb chronologies were established(covering 150 years) using the constant rate of supply(CRS) model. The measured Pb contents ranged from 14.97 mg/kg to 29.40 mg/kg with average values of 17.17–22.79 mg/kg, and the Pb fluxes ranged from 41.70 mg/(m~2·yr) to 172.70 mg/(m~2·yr) with averages of 95.59–123.41 mg/(m~2·yr). Temporal variations of Pb flux, enrichment factors and Pb isotopes show a gradual and continuous increase over time and clearly reflect increased emissions from anthropogenic activities in the region. The Pb isotopic compositions show that most of Pb deposition in Yancheng wetland is input from natural sources by water flows and has the same levels of Pb as in the surface sediment of the Yangtze River and the Pacific mineral aerosol. We also stress the anthropogenic Pb contribution in Yangcheng wetland sediment and the reason of our Pb isotopes not showing anthropogenic signature is likely the instability of anthropogenic Pb in high Fe/Mn oxide conditions. Therefore, more attention should be paid to current local pollution problems, and society should take action to seek a balance between economic development and environmental protection.     

Change of Soil Organic Carbon after Cropland Afforestation in ′Beijing-Tianjin Sandstorm Source Control′ Program Area in China

Land use change is one of the major factors that affect soil organic carbon(SOC) variation and global carbon balance. However, the effects of land use change on SOC are always variable. In this study, using a series of paired-field experiments, we estimated the effects of revegetation types and environmental conditions on SOC stock and vertical distribution after replacement of cropland with poplar(Populus tomentosa) and korshinsk peashrub(Caragana korshinskii) in three climate regions(Chifeng City, Fengning City and Datong City of the ′Beijing-Tianjin Sandstorm Source Control′(BTSSC) program area. The results show that SOC sequestration rate ranges from 0.15 Mg/(ha·yr) to 3.76 Mg/(ha·yr) in the soil layer of 0–100 cm in early stage after cropland afforestation in the BTSSC program area. The SOC accumulation rates are the highest in Fengning for both the two vegetation types. Compared to C. korshinskii, P. tomentosa has greater effects on SOC accumulation in the three climate regions, but significantly greater effect only appears in Datong. The SOC density increases by 20%–111% and 15%–59% for P. tomentosa and 9%–63% and 0–73% for C. korshinskii in the 0–20 cm and 20–100 cm soil layers, respectively. Our results indicate that cropland afforestation not only affects SOC stock in the topsoil, but also has some effects on subsoil carbon. However, the effect of cropland afforestation on SOC accumulation varied with climate regions and revegetation types. Considering the large area of revegetation and relatively high SOC accumulation rate, SOC sequestration in the BTSSC program should contribute significantly to decrease the CO2 concentration in the atmosphere.     

Distribution and accumulation of soil carbon in temperate wetland,northeast China

Estimating carbon sequestration and nutrient accumulation rates in Northeast China are important to assess wetlands function as carbon sink buffering greenhouse gas increasing in North Asia. The objectives of this study were to estimate accreting rates of carbon and nutrients in typical temperate wetlands. Results indicated that average soil organic carbon(SOC), total nitrogen(TN) and total phosphorus(TP) contents were 37.81%, 1.59% and 0.08% in peatlands, 5.33%, 0.25% and 0.05% in marshes, 2.92%, 0.27% and 0.10% in marshy meadows, respectively. Chronologies reconstructed by 210 Pb in the present work were acceptable and reliable, and the average time to yield 0–40 cm depth sediment cores was 150 years. Average carbon sequestration rate(Carbonsq), nitrogen and phosphorus accumulation rates were 219.4 g C/(m~2·yr), 9.16 g N/(m~2·yr) and 0.46 g P/(m~2·yr) for peatland; 57.13 g C/(m~2·yr), 5.42 g N/(m~2·yr) and 2.16 g P/(m~2·yr) for marshy meadow; 78.35 g C/(m~2·yr), 8.70 g N/(m~2·yr) and 0.71 g P/(m2·yr) for marshy; respectively. Positive relations existed between Carbonsq with nitrogen and precipitations, indicating that Carbonsq might be strengthened in future climate scenarios.     

Spatial-temporal variability of throughfall in a subtropical deciduous forest from the hilly regions of eastern China

Throughfall variability plays a crucial role in regulating hydrological and biogeochemical processes in forest ecosystems. However, throughfall variability and its potential influencing factors remain unclear in the subtropical deciduous forest because of its complex canopy and meteorological conditions. Here, the spatial variability and temporal stability of throughfall were investigated from October 2016 to December 2017 within a deciduous forest in the subtropical hilly regions of eastern China, and the effects of meteorological variables and distance from nearest tree trunk on throughfall variability were systematically evaluated. Throughfall variability during the leafed period was slightly higher than that during the leafless period inferred from the coefficient of variation of throughfall amounts(CVTF), with 13.2%-40.9% and 18.7%-31.9%, respectively. The multiple regression model analysis suggested that the controlling factors of throughfall variability were different in studied periods: Maximum 10-min rainfall intensity, wind speed and air temperature were the dominant influencing factors on throughfall variability during the leafed period, with the relative contribution ratio(RCR) of 25.9%, 18.7% and 8.9%, respectively. By contrast, throughfall variability was affected mainly by the mean rainfall intensity(RCR=40.8%) during the leafless period. The temporal stability plots and geostatistical analysis indicated that spatial patterns of throughfall were stable and similar among rainfall events. Our findings highlight the important role of various meteorological factors in throughfall variability and are expected to contribute to the accurate assessment of throughfall, soil water and runoff within the subtropical forests.     

Carbon sequestration in forest vegetation of Beijing at sublot level

Based on forest inventory data (FID) at sublot level,we estimated the carbon sequestration in forest vegetation of Beijing,China in 2009.In this study,the carbon sequestration in forest vegetation at sublot level was calculated based on net biomass production (ΔB) which was estimated with biomass of each sublot and function relationships between ΔB and biomass.The biomass of forested land was calculated with biomass expansion factors (BEFs) method,while those of shrub land and other forest land types were estimated with biomass,coverage and height of referred shrubs and shrub coverage and height of each sublot.As one of special forested land types,the biomass of economic tree land was calculated with biomass per tree and tree number.The variation of carbon sequestration in forest vegetation with altitude,species and stand age was also investigated in this study.The results indicate that the carbon sequestration in forest vegetation in Beijing is 4.12 × 106 tC/yr,with the average rate of 3.94 tC/(ha·yr).About 56.91% of the total carbon sequestration in forest vegetation is supported by the forest in the plain with an altitude of < 60 m and the low mountainous areas with an altitude from 400 m to 800 m.The carbon sequestration rate in forest vegetation is the highest in the plain area with an altitude of < 60 m and decreased significantly in the transitional area from the low plain to the low mountainous area with an altitude ranging from 200 m to 400 m due to intensive human disturbance.The carbon sequestration of Populus spp.forest and Quercus spp.forest are relatively higher than those of other plant species,accounting for 25.33% of the total.The carbon sequestration in vegetation by the forest of < 40 years amounts to 45.38% of the total.The carbon sequestration rate in forest vegetation peaks at the stand age of 30–40 years.Therefore,it would be crucial for enhancing the capability of carbon sequestration in forest vegetation to protect the forest in Beijing,to limit human disturbance in the transitional area from the plain to the low mountain area,and to foster the newly established open forest.     

Interception of sulfate deposition from a closed canopy to a forest gap edge canopy in a subalpine dragon spruce plantation

Reducing the threats of sulfate ion(SO_4~(2-))deposition to terrestrial ecosystems is a great challenge.The canopy interception effect on SO_4~(2-)deposition has been well documented,but the interception efficiency of the gap edge remains unknown.Therefore,a subalpine dragon spruce(Picea asperata) plantation was evaluated in the upper reaches of the Yangtze River.The dynamics of the SO_4~(2-) concentration in the throughfall were investigated from the gap edge to the closed canopy during the rainfall and snowfall periods from August 2015 to July 2016.The annual input of SO_4~(2-) totaled 2.56 kg/ha through rainfall and 0.69 kg/ha through snowfall.The total annual net interception fluxes(NIFs) of SO_4~(2-) at the gap edge and in the closed canopy were 1.48 kg/ha and 0.66 kg/ha,respectively,and the net interception ratios(NIRs) accounted for 45.40% and 20.25%,respectively.The NIF and the NIR of SO_4~(2-) at the gap edge were higher than those in the closed canopy.Therefore,the results suggested that a significant amount of SO_4~(2-) deposition was intercepted by the tree canopy in the subalpine plantation,with more SO_4~(2-) deposition at the gap edge than in the closed canopy,which is beneficial for improving the water quality in the upper reaches of the Yangtze River via forest management.     

Simulating Carbon Sequestration and GHGs Emissions in Abies fabric Forest on the Gongga Mountains Using a Biogeochemical Process Model Forest-DNDC

The process-oriented model Forest-DNDC describing biogeochemical cycling of C and N and GHGs (greenhouse gases) fluxes (CO2, NO and N2O) in forest ecosystems was applied to simulate carbon sequestration and GHGs emissions in Abies fabric forest of the Gongga Mountains at southeastern edge of the Tibetan Plateau. The results indicated that the simulated gross primary production (GPP) of Abies fabric forest was strongly affected by temperature. The annual total GPP was 24,245.3 kg C ha-1 yr-1 for 2005 and 26,318.8 kg C ha-1 yr-1 for 2006, respectively. The annual total net primary production (NPP) was 5,935.5 and 4,882.2 kg C ha-1 yr-1 for 2005 and 2006, and the annual total net ecosystem production (NEP) was 4,815.4 and 3,512.8 kg C ha-1 yr-1 for 2005 and 2006, respectively. The simulated seasonal variation in CO2 emissions generally followed the seasonal variations in temperature and precipitation. The annual total CO2 emissions were 3,109.0 and 4,821.0 kg C ha-1 yr-1 for 2005 and 2006, the simulated annual total N2O emissions from forest soil were 1.47 and 1.36 kg N ha-1 yr-1 for 2005 and 2006, and the annual total NO emissions were 0.09 and 0.12 kg N ha-1 yr-1 for 2005 and 2006, respectively.     

Soil carbon stock and flux in plantation forest and grassland ecosystems in Loess Plateau,China

Carbon sequestration occurs when cultivated soils are re-vegetated. In the hilly area of the Loess Plateau, China, black locust(Robinia pseudoacacia) plantation forest and grassland were the two main vegetation types used to mitigate soil and water loss after cultivation abandonment. The purpose of this study was to compare the soil carbon stock and flux of these two types of vegetation which restored for 25 years. The experiment was conducted in Yangjuangou catchment in Yan′an City, Shaanxi Province, China. Two adjacent slopes were chosen for this study. Six sample sites were spaced every 35–45 m from summit to toe slope along the hill slope, and each sample site contained three sampling plots. Soil organic carbon and related physicochemical properties in the surface soil layer(0–10 cm and 10–20 cm) were measured based on soil sampling and laboratory analysis, and the soil carbon dioxide(CO2) emissions and environmental factors were measured in the same sample sites simultaneously. Results indicated that in general, a higher soil carbon stock was found in the black locust plantation forest than that in grassland throughout the hill slope. Meanwhile, significant differences in the soil carbon stock were observed between these two vegetation types in the upper slope at soil depth 0–10 cm and lower slope at soil depth 10–20 cm. The average daily values of the soil CO2 emissions were 1.27 μmol/(m2·s) and 1.39 μmol/(m2·s) for forest and grassland, respectively. The soil carbon flux in forest covered areas was higher in spring and less variation was detected between different seasons, while the highest carbon flux was found in grassland in summer, which was about three times higher than that in autumn and spring. From the carbon sequestration point of view, black locust plantation forest on hill slopes might be better than grassland because of a higher soil carbon stock and lower carbon flux.     

Effects of aluminum toxicity induced by acid deposition on pine forest ecosystem in Longli of Guizhou Province,Southwestern China

The effects of acid deposition on pine forest ecosystems in Longli of Guizhou Province, southwestern China are studied using indoor experiments and model simulations. Indoor experiments are designed to explore the aluminum toxicity on pine seedlings, and the long-term soil acidification model（LTSAM） and a terrestrial biogeochemistry model（CENTURY） are used to simulate the influences of acid deposition on pine forest ecosystems. The indoor experiment results of aluminum toxicity show that aluminum ions in solution limit plant growth and acid deposition enhances this effect by facilitating the release of aluminum ions from the soil. Pine seedling biomass and root elongation decrease as the aluminum concentration increases. The results of model simulations show that the soil chemistry varies significantly with different changes in acid deposition. When the acid deposition increases, the pH value in the soil solution decreases and the soil Al³⁺ concentration increases. The increased acid deposition also has negative impacts on the forest ecosystem, i.e., decreases plant biomass, net primary productivity（NPP） and net CO₂ uptake. As a result, the soil organic carbon（SOC） decreases because of the limited supply of decomposition material. Thus acid deposition need be reduced to help protect the forest ecosystems.     

Drivers of coastal bacterioplankton community diversity and structure along a nutrient gradient in the East China Sea

Anthropogenic nutrient discharge poses widespread threats to coastal ecosystems and has increased environmental gradients from coast to sea. Bacterioplankton play crucial roles in coastal biogeochemical cycling, and a variety of factors af fect bacterial community diversity and structure. We used 16 S r RNA gene pyrosequencing to investigate the spatial variation in bacterial community composition(BCC) across five sites on a coast-of fshore gradient in the East China Sea. Overall, bacterial alpha-diversity did not diff er across sites, except that richness and phylogenetic diversity were lower in the of fshore sites, and the highest alpha-diversity was found in the most landward site, with Chl-abeing the main factor. BCCs generally clustered into coastal and of fshore groups. Chl-a explained 12.3% of the variation in BCCs, more than that explained by either the physicochemical(5.7%) or spatial(8.5%) variables. Nutrients(particularly nitrate and phosphate), along with phytoplankton abundance, were more important than other physicochemical factors, co-explaining 20.0% of the variation in BCCs. Additionally, a series of discriminant families(primarily affiliated with Gammaproteobacteria and Alphaproteobacteria), whose relative abundances correlated with Chl-a, DIN, and phosphate concentrations, were identified, implying their potential to indicate phytoplankton blooms and nutrient enrichment in this marine ecosystem. This study provides insight into bacterioplankton response patterns along a coast-of fshore gradient, with phytoplankton abundance increasing in the of fshore sites. Time-series sampling across multiple transects should be performed to determine the seasonal and spatial patterns in bacterial diversity and community structure along this gradient.     

Water quality and eutrophication in the Guangzhou Sea Zone of the Pearl River estuary

To gain a better understanding of water quality and eutrophication, we investigated the seasonal and spatial distribution of water quality at 17 stations in the Guangzhou Sea Zone (GZSZ). Nutrients, chlorophyll-a (Chl-a), salinity, chemical oxygen demand, and other physical and chemical parameters were determined in February, May, August and October from 2005 to 2007. The concentrations showed ranges of 93.2–530.4 μmol/L for dissolved inorganic nitrogen (DIN), 0.62–3.16 μmol/L for phosphate (PO₄-P) and 50–127 μmol/L for silicate (SiO₃-Si). The results indicated that DIN was strongly influenced by domestic sewage coming from Guangzhou City and NO₃-N was the main form of DIN in most areas, while concentrations of phosphate and silicate were generally controlled by Pearl River runoff, land-based sources along the land or islands, and algae assimilation. N/P ratios were very high in both dry season and wet season, and varied from 57 to 667, suggesting that P was potentially the most limiting nutrient in the GZSZ. The concentrations of Chl-a were 3–96 μg/L, and were highly correlated with the distribution characteristics of COD. The concentrations of nutrients have increased over the past two decades (1982–2007). This means it is necessary to control the input of nutrients to the GZSZ, especially that of phosphate.     

Simulating carbon sequestration and GHGs emissions in <Emphasis Type="Italic">Abies fabric</Emphasis> forest on the Gongga Mountains using a biogeochemical process model Forest-DNDC

The process-oriented model Forest-DNDC describing biogeochemical cycling of C and N and GHGs （greenhouse gases） fluxes （CO2, NO and N2O） in forest ecosystems was applied to simulate carbon sequestration and GHGs emissions in Abies fabric forest of the Gongga Mountains at southeastern edge of the Tibetan Plateau. The results indicated that the simulated gross primary production （GPP） of Abies fabric forest was strongly affected by temperature. The annual total GPP was 24,245.3 kg C ha^-1 yr^-1 for 2005 and 26,318.8 kg C ha^-1 yr^-1 for 2006, respectively. The annual total net primary production （NPP） was 5,935.5 and 4,882.2 kg C ha^-1 yr^-1 for 2005 and 2006, and the annual total net ecosystem production （NEP） was 4,815.4 and 3,512.8 kg C ha^-1 yr^-1 for 2005 and 2006, respectively. The simulated seasonal variation in CO2 emissions generally followed the seasonal variations in temperature and precipitation. The annual total CO2 emissions were 3,109.0 and 4,821.0 kg C ha^-1 yr^-1 for 2005 and 2006, the simulated annual total N2O emissions from forest soil were 1.47 and 1.36 kg N ha^-1 yr^-1 for 2005 and 2006, and the annual total NO emissions were 0.09 and o.12 kg N ha^-1 yr^-1 for 2005 and 2006, respectively.     

“一带一路”沿线国家农田生态系统脆弱性及其对气候变化的响应

全球气候变化背景下,“一带一路”沿线国家农田生态系统脆弱性直接影响着所在国家或地区的粮食安全问题。本文基于农田生态系统总初级生产力（GPP）,使用定量的脆弱性评价方法,系统分析了“一带一路”沿线国家农田生态系统脆弱性的空间分布特征及其对气候变化的响应。结果表明：① “一带一路”沿线国家农田生态系统脆弱性普遍处于较高的程度,77.1%的农田生态系统表现为中度和重度脆弱,且农田生态系统脆弱性呈现出明显的空间分异格局,中亚、西亚和蒙古脆弱性较高,中国、东南亚和南亚的脆弱性处于中等水平,俄罗斯、独联体和中东欧脆弱性较低;② 1980年以来“一带一路”沿线农田生态系统暖干化趋势明显,暖干化区域面积占64.06%,暖干化是“一带一路”沿线国家农田生态系统气候变化的主要特征;③ 农田生态系统脆弱性由低到高的气候变化区依次为暖湿区、冷湿区、暖干区、冷干区。暖湿区农田生态系统脆弱性最低,而冷干区农田生态系统脆弱性最高。气温和降水的变化及其耦合关系控制着农田生态系统脆弱性程度,其中降水变化趋势是影响农田生态系统脆弱性的重要因子。本研究为“一带一路”沿线国家应对和解决粮食安全问题,促进农业可持续发展,为加强各国之间的农业国际合作提供科学依据和有益参考。     

CHANGE OF NUTRIENT IMPORT AND EXPORT IN PROCESS OF RAINFALL IN AILAO MOUNTAIN OF YUNNAN PROVINCE

ＣＨＡＮＧＥ　ＯＦ　ＮＵＴＲＩＥＮＴ　ＩＭＰＯＲＴ　ＡＮＤ　ＥＸＰＯＲＴ　ＩＮ　ＰＲＯＣＥＳＳ　ＯＦ　ＲＡＩＮＦＡＬＬ　ＩＮ　ＡＩＬＡＯ　ＭＯＵＮＴＡＩＮ　ＯＦ　ＹＵＮＮＡＮ　ＰＲＯＶＩＮＣＥＧａｎＪｉａｎｍｉｎ（甘健民）；ＸｕｅＪｉｎｇｙｉ（薛敬意...     

Regional variation in carbon sequestration potential of forest ecosystems in China

Enhancing forest carbon(C) storage is recognized as one of the most economic and green approaches to offsetting anthropogenic CO_2 emissions. However, experimental evidence for C sequestration potential(C_(sp)) in China's forest ecosystems and its spatial patterns remain unclear, although a deep understanding is essential for policy-makers making decisions on reforestation. Here, we surveyed the literature from 2004 to 2014 to obtain C density data on forest ecosystems in China and used mature forests as a reference to explore C_(sp). The results showed that the C densities of vegetation and soil(0–100 cm) in China's forest ecosystems were about 69.23 Mg C/ha and 116.52 Mg C/ha, respectively. In mature forests, the C_(sp) of vegetation and soil are expected to increase to 129.26 Mg C/ha(87.1%) and 154.39 Mg C/ha(32.4%) in the coming decades, respectively. Moreover, the potential increase of C storage in vegetation(10.81 Pg C) is estimated at approximately twice that of soil(5.01 Pg C). Higher C_(sp) may occur in the subtropical humid regions and policy-makers should pay particular attention to the development of new reforestation strategies for these areas. In addition to soil nutrients and environment, climate was an important factor influencing the spatial patterns of C density in forest ecosystems in China. Interestingly, climate influenced the spatial patterns of vegetation and soil C density via different routes, having a positive effect on vegetation C density and a negative effect on soil C density. This estimation of the potential for increasing forest C storage provided new insights into the vital roles of China's forest ecosystems in future C sequestration. More importantly, our findings emphasize that climate constraints on forest C sequestration should be considered in reforestation strategies in China because the effects of climate were the opposite for spatial patterns of C density in vegetation and soil.Enhancing forest carbon(C) storage is recognized as one of the most economic and green approaches to offsetting anthropogenic CO2 emissions. However, experimental evidence for C sequestration potential(Csp) in China's forest ecosystems and its spatial patterns remain unclear, although a deep understanding is essential for policy-makers making decisions on reforestation. Here, we surveyed the literature from 2004 to 2014 to obtain C density data on forest ecosystems in China and used mature forests as a reference to explore Csp. The results showed that the C densities of vegetation and soil(0–100 cm) in China's forest ecosystems were about 69.23 Mg C/ha and 116.52 Mg C/ha, respectively. In mature forests, the Csp of vegetation and soil are expected to increase to 129.26 Mg C/ha(87.1%) and 154.39 Mg C/ha(32.4%) in the coming decades, respectively. Moreover, the potential increase of C storage in vegetation(10.81 Pg C) is estimated at approximately twice that of soil(5.01 Pg C). Higher Csp may occur in the subtropical humid regions and policy-makers should pay particular attention to the development of new reforestation strategies for these areas. In addition to soil nutrients and environment, climate was an important factor influencing the spatial patterns of C density in forest ecosystems in China. Interestingly, climate influenced the spatial patterns of vegetation and soil C density via different routes, having a positive effect on vegetation C density and a negative effect on soil C density. This estimation of the potential for increasing forest C storage provided new insights into the vital roles of China's forest ecosystems in future C sequestration. More importantly, our findings emphasize that climate constraints on forest C sequestration should be considered in reforestation strategies in China because the effects of climate were the opposite for spatial patterns of C density in vegetation and soil.     

Mushroom production as an alternative for rural development in a forested mountainous area

Wild mushrooms are recognized as important non-wood forest products in mountainous ecosystems, but their real potential for generating rural economies has not been fully evaluated due to the difficulties in obtaining reliable productivity data, minimizing their true potential as contributor to rural economies. Mushroom yield models based on large data series from Pinus forest ecosystems in the region of Catalonia(Spain), combined with data from the Spanish National Forest Inventory allow us to estimate the potential mushroom productivity by forest ecosystems. The results of 24,500 tons/yr of mushrooms of which 16,300 tons are classified as edible and 7,900 tons are commonly marketed demonstrate the importance of mushroom productions in Catalonian pine forests, mostly located in mountainous areas where the development of agricultural activities is limited. Economic mushroom value is estimated at 48 million € for the edible mushroom and 32 million € for those corresponding to marketable yields, confirming the potential of this non-wood forest product. These production results and corresponding economic values provide a basis for the incorporation of wild mushrooms as significant non-wood forest products in the development of forest policies in mountainous areas.     

Characteristics of nutrients in the Jiulong River and its impact on Xiamen Water, China

Water samples were collected at 20 sites on 4 occasions in 2009(twice in May,and once in both August and November) along the Jiulong River,South China to examine how nutrient inputs from the Jiulong River could affect the nutrient status of the Xiamen Water.Samples were analyzed for nitrite(NO2-N),nitrate(NO3-N),ammonium(NH4-N),phosphate(PO4-P),silicate(SiO3-Si),salinity,and temperature,to determine the nutrient and trophic status of the river.The results indicate that nutrients are derived mainly from river runoff.NO3-N was the main form of DIN in most parts of the river.In addition,NO3-N,DIN,and SiO3-Si behave conservatively.There is a surplus of DIN and SiO3-Si in the river,and PO4-P is a limitation on phytoplankton growth.The concentration of DIN is typically above 0.60 mg/dm3,and higher than 1.00 mg/dm3in most parts of the river.The concentration of PO4-P is typically above 0.02 mg/dm3,while the concentration of SiO3-Si is higher than 1.00 mg/dm3.Between 2003 and 2008,samples were collected 3 times per year(May,August and November) at 27 sites in the Xiamen Water and analyzed for NO2-N,NO3-N,NH4-N,PO4-P,salinity,and temperature.We discovered that the Jiulong River was the key source of DIN into the Xiamen Water,but not PO4-P,indicating the reason of the N/P molar ratio imbalance in the Xiamen Water.In the future,the effects of high DIN concentrations on the phytoplankton communities and marine ecosystems of the Xiamen Water shall be studied.     

Spatial variability of soil carbon to nitrogen ratio and its driving factors in Ili River valley,Xinjiang, Northwest China

Soil carbon to nitrogen(C/N) ratio is one of the most important variables reflecting soil quality and ecological function,and an indicator for assessing carbon and nitrogen nutrition balance of soils.Its variation reflects the carbon and nitrogen cycling of soils.In order to explore the spatial variability of soil C/N ratio and its controlling factors of the Ili River valley in Xinjiang Uygur Autonomous Region,Northwest China,the traditional statistical methods,including correlation analysis,geostatistic alanalys and multiple regression analysis were used.The statistical results showed that the soil C/N ratio varied from 7.00 to 23.11,with a mean value of 10.92,and the coefficient of variation was 31.3%.Correlation analysis showed that longitude,altitude,precipitation,soil water,organic carbon,and total nitrogen were positively correlated with the soil C/N ratio(P 0.01),whereas negative correlations were found between the soil C/N ratio and latitude,temperature,soil bulk density and soil p H.Ordinary Cokriging interpolation showed that r and ME were 0.73 and 0.57,respectively,indicating that the prediction accuracy was high.The spatial autocorrelation of the soil C/N ratio was 6.4 km,and the nugget effect of the soil C/N ratio was 10% with a patchy distribution,in which the area with high value(12.00–20.41) accounted for 22.6% of the total area.Land uses changed the soil C/N ratio with the order of cultivated land grass land forest land garden.Multiple regression analysis showed that geographical and climatic factors,and soil physical and chemical properties could independently explain 26.8%and 55.4% of the spatial features of soil C/N ratio,while human activities could independently explain 5.4% of the spatial features only.The spatial distribution of soil C/N ratio in the study has important reference value for managing soil carbon and nitrogen,and for improving ecological function to similar regions.     

Nutrient and eutrophication characteristics of the Dongshan Bay,South China

We recorded NO 3-N, NO 2-N, NH 4-N, PO 4-P, SiO 3-Si, salinity, and temperature data at 10 stations in the Dongshan Bay in May, June, July, August, October, and November 2008, analyzing nutrient and eutrophication characteristics. The mean concentration of dissolved inorganic nitrogen(DIN) was 0.30–0.40 mg/dm 3; generally, NO 3-N was the main form in most areas. The mean concentrations of PO 4-P and SiO 3-Si were 0.040–0.060 mg/dm 3 and 1.00–1.50 mg/dm 3, respectively. We proved that the majority of the SiO 3-Si in the Dongshan Bay came from the Zhangjiang River, with some coming from the Bachimen Strait. DIN originated from both the Zhangjiang River and the Bachimen Strait. Most PO 4-P originated from the Bachimen Strait, and some came from the Zhangjiang River. We found that P was an overall limiting factor to the phytoplankton community in most of the Dongshan Bay, and that Si and N were in surplus. However, near the Bachimen Strait Si became a limiting factor, especially for diatoms, while P and N were in comparative surplus. We used a potential eutrophication assessment method to analyze eutrophication, and showed that the most serious eutrophication occurred near the Zhangjiang River estuary and near the Bachimen Strait. In 2008, DIN levels were four times higher than that in 1988; PO 4-P levels were threefold higher, while SiO 3-Si was approximately double. Dissolved nutrients increased between 1988 and 2008. DIN increased at the greatest rate comparing to PO 4-P and SiO 3-Si, thus the N/P and N/Si mol ratios increased. Further studies on the effects of high DIN concentrations on the phytoplankton communities and marine ecosystems of the Dongshan Bay are needed.     

CARBON CYCLE IN SHRIMP POLYCULTURE MESOCOSM

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