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Soil organic carbon (SOC) in coastal wetlands, also known as "blue C," is an essential component of the global C cycles. To gain a detailed insight into blue C storage and controlling factors, we studied 142 sites across ca. 5000 km of coastal wetlands, covering temperate, subtropical, and tropical climates in China. The wetlands represented six vegetation types (Phragmites australis, mixed of P. australis and Suaeda, single Suaeda, Spartina alterniflora, mangrove [Kandelia obovata and Avicennia marina], tidal flat) and three vegetation types invaded by S. alterniflora (P. australis, K. obovata, A. marina). Our results revealed large spatial heterogeneity in SOC density of the top 1-m ranging 40-200 Mg C ha

1. Exotic plant invasion has been changing the vegetation composition and function of terrestrial ecosystems. Nitrogen (N) and phosphorus (P) are often the limiting nutrients for terrestrial plants. However, under invasive pressure, in situ plant N and P usage mechanisms remain poorly understood but are pivotal for a better understanding of plant invasion and coexistence in invaded ecosystems. 2. Nitrogen and P concentrations, natural N-15 abundance (delta N-15 values) were investigated in leaves and soils under different invasive pressures (here expressed as the biomass percentages of invasive plants in each plot) for two invasive species (Chromolaena odorata and Ageratina adenophora) in Xishuangbanna in tropical China. 3. Soil N and P concentrations revealed the relatively N-rich but P-poor status of our study site. Under invasion, soil inorganic N (dominated by ammonium) and available P did not increase significantly. The leaf N and P of invasive plants increased, while leaf N increased but P decreased for native species. Natural delta N-15 mass balance between leaves and soil inorganic N sources revealed that ammonium dominated N utilization in both natives and invaders. Invasive plants showed ammonium utilization with increasing leaf N levels, while native plants under no invasion showed nitrate utilization with increasing leaf N levels. 4. Synthesis. Increased soil ammonium availability contributed to preferential ammonium utilization by invasive plants and elevated ammonium utilization in natives, but the P competition of natives decreased in invaded ecosystems. These novel insights into nutrient dynamics in invaded ecosystems enhance our understanding of plant invasion and coexistence mechanisms.

The concentration and isotopic composition of nitrate were analyzed to improve an understanding of nitrate sources and transformation processes in a typical karstic agricultural field in the Houzhai catchment, Guizhou Province, Southwest China. The results revealed that no distinct spatial pattern of content and isotopic composition of nitrate exists in this karst catchment. Nitrate in surface stream (SFS) had slightly lighter isotopic composition and lower concentration compared with nitrate in subterranean stream (STS) during the dry season. Concentrations of SFS nitrate increased to concentrations similar to those of STS during the wet season. The isotopic values indicated that nitrate were mainly impacted by manure sources during the dry season and influenced by a mix of chemical fertilizer and manure during the wet season. The denitrification rates were roughly estimated based on the isotopic compositions of nitrate after considering volatilization and ignoring assimilation. The calculated result showed that approximately one fifth of nitrate load was removed by denitrification in the catchment. Annual nitrate flux from the outlets accounted for 14.2% of applied total fertilizers used in the catchment, approximately 85% of total transported flux from the catchment in the wet season. Furthermore, chemical weathering processes were enhanced by using nitrogen fertilizer because liberated protons and enhanced HCO3− flux were produced through by nitrification. Copyright © 2014 John Wiley & Sons, Ltd.

The contents and stable S isotope ratio (δS) values of total S, organic S, SO-S, and total reduced inorganic S (TRS) in typical limestone soil and yellow soil were analyzed in this study to examine the general distributions of S forms and their δS values in soils in karst areas of southwest China. Under a similar level of acid deposition, the vertical profiles of the S forms and their δS values differed in limesto\ne soil and yellow soil, indicating the different geochemical responses of these soils to acid deposition. The deposited SO was retained as organic S in both soils. The depletion in S of TRS relative to SO and the parallel increasing δS values of TRS and SO indicate a bacterial reduction process of sulfate in both soils. The different extents of C-bonded S mineralization and organic sulfate transport explain the different vertical profiles of total S and organic S contents in both soils. Sulfate adsorption in limestone soil was negligible because of high pH values. Sulfate adsorption in yellow soil was another important S retention process in addition to biological S retention to form organic S and TRS because of low pH values. The effect of acid deposition on yellow soil appeared more serious because of the accumulation and leaching of deposited SO, which can result in soil acidification and accelerate the loss of basic cations from yellow soil. However, compared with yellow soil, limestone soil released more S into rivers by organic S mineralization after a large decrease in annual S deposition rate.

Mosses, among all types of terrestrial vegetation, are excellent scavengers of anthropogenic nitrogen (N), but their utilization of dissolved organic N (DON) and their reliance on atmospheric N remain uncharacterized in natural environments, which obscures their roles in N cycles. Natural (15) N abundance of N sources (nitrate (NO(3)(-)), ammonium (NH(4)(+)) and DON in deposition and soil) for epilithic and terricolous mosses was analyzed at sites with different N depositions at Guiyang, China. Moss NO(3)(-) assimilation was inhibited substantially by the high supply of NH(4)(+) and DON. Therefore, contributions of NH(4)(+) and DON to moss N were partitioned using isotopic mass-balance methods. The N contributions averaged 56% and 46% from atmospheric NH(4)(+), and 44% and 17% from atmospheric DON in epilithic and terricolous mosses, respectively. In terricolous mosses, soil NH(4)(+) and soil DON accounted for 16% and 21% of bulk N, which are higher than current estimations obtained using (15) N-labeling methods. Moreover, anthropogenic NH(4)(+) deposition suppressed utilization of DON and soil N because of the preference of moss for NH(4)(+) under elevated NH(4)(+) deposition. These results underscore the dominance of, and preference for, atmospheric NH(4)(+) in moss N utilization, and highlight the importance of considering DON and soil N sources when estimating moss N sequestration and the impacts of N deposition on mosses.

To better understand the Fe isotope characteristics of natural samples in the Karst area, the Fe isotope compositions of riverine suspended particulates, lake suspended particulates, lake sediments, porewaters, phytoplanktons, and aerosols in the watersheds of Lake Aha (a mineralized water system) and Lake Hongfeng (a mesotrophic water system), which are located in the Karst area, southwest China, were investigated. The studied samples displayed a variable range between δ56Fe=–2.03‰ and 0.36‰. Aerosols and phytoplanktons have similar or slightly heavier Fe isotope compositions relative to the average of igneous rocks. Fe isotope compositions of riverine Suspended Particulate Matter (SPM) were mainly affected by the types of tributaries. Suspended particulates collected from tributaries seriously contaminated with coal mine drainages displayed negative δ56Fe values (–0.89‰ to –0.31‰) during summer, and there were significant increases of δ56Fe values in winter, except AR2, which was polluted with both coal mine drainage and sewage effluent. Characteristics of lakes have important influences on Fe isotope compositions of suspended particulates, lake sediments, and porewaters. The epilimnetic particulate Fe of Lake Hongfeng had δ56Fe=–0.04‰ to 0.13‰, while lighter Fe isotope compositions were measured for particulate Fe from Lake Aha, ranging from –0.42‰ to –0.09‰. Sediments collected from Hou Wu (HW) station of Lake Hongfeng have an average δ56Fe value of 0.09‰ and their corresponding porewaters have lighter Fe isotope compositions, ranging from –0.57‰ to –0.31‰; no significant variations have been observed. For the Liang Jiang Kou (LJK) station of Lake Aha, the content of reactive Fe and the concentration of sulfate were all high. Due to the reactive Fe recycling, including dissimilatory Fe reduction, adsorption, and Fe–sulfide formation, porewaters sampled near the sediment surface have been found to have a δ56Fe value as low as –2.03‰ and an increase up to 0.12‰, with a burial depth of 10 cm. In contrast, an opposite variation trend was found for LJK sediments. Sediments sampled at 1-cm depth had a value of δ56Fe=–0.59‰ and decrease as low as –1.75‰ with burial depth. This investigation demonstrated that significant Fe isotope fractionations occur in surface environments. Fe isotope compositions of particulate Fe were seriously affected by Fe sources, and Fe biogeochemical recycling has an important influence on Fe isotope fractionations in lake sediments, especially when there are significant amounts of reactive Fe and sulfate.

Traditionally-suggested combustion time of 1 h at 550°C) with the sealed-tube combustion method for determining the 13C/ 12C ratio of cellulose nitrate or other nitrogen-containing components could produce large negative deviation up to 1°. Three types of cellulose are used to ascertain possible causes. The presence of nitrous oxide (N2O) formed during combustion is most likely responsible for this deviation. Prolongation of the combustion time (at least 5 h at 550°C) and intimate contact between copper oxide and organic matter can greatly improve the analysis precision and effectively reduce this deviation to an acceptable level. Regardless of scattered carbon isotope data, hydrogen isotope data are all reproducible within 2° when this method is coupled with the high temperature uranium reduction method. Thus, care should be taken for determining carbon and nitrogen isotope compositions of nitrogen-containing substances using the low temperature sealed-tube combustion method.

Groundwater is a very significant water source used for irrigation and drinking purposes in the karst region, and therefore understanding the hydrogeochemistry of karst water is extremely important. Surface water and groundwater were collected, and major chemical compositions and environmental isotopes in the water were measured in order to reveal the geochemical processes affecting water quality in the Gaoping karst basin, southwest China. Dominated by Ca 2+ , Mg 2+ , HCO 3 ― and SO 4 2― , the groundwater is typically characterized by Ca―Mg―HCO 3 type in a shallow aquifer, and Ca―Mg―SO 4 type in a deeper aquifer. Dissolution of dolomite aquifer with gypsiferous rocks and dedolomitization in karst aquifers are important processes for chemical compositions of water in the study basin, and produce water with increased Mg 2+ , Ca 2+ and SO 4 2― concentrations, and also increased TDS in surface water and groundwater. Mg 2 +/Ca 2+ molar ratios in groundwater decrease slightly due to dedolomitization, while the mixing of discharge of groundwater with high Mg 2+ /Ca 2+ ratios may be responsible for Mg 2+ /Ca 2+ ratios obviously increasing in surface water, and Mg 2+ /Ca 2+ ratios in both surface water and groundwater finally tending to a constant. In combination with environmental isotopic analyses, the major mechanism responsible for the water chemistry and its geochemical evolution in the study basin can be revealed as being mainly from the water―rock interaction in karst aquifers, the agricultural irrigation and its infiltration, the mixing of surface water and groundwater and the water movement along faults and joints in the karst basin.

SUMMARY The species composition, the net photosynthetic O2 evolution rate and the activity of external carbonic anhydrase (CA) of microalgae from three reservoirs were studied. Carbonic anhydrase activity had a significant positive correlation with the density of Cyanobacteria in Lake Aha. Microalgae's carbonic anhydrase activity in Lakes Baihua and Hongfeng was related to the density of Chlorophyceae. The species abundances of microalgae in Lake Aha, Lake Baihua, and Lake Hongfeng were different. A relationship between carbonic anhydrase activity and net photosynthetic O2 evolution rate had also been established. Algae with external CA influenced the algal productivity. These results demonstrate the role of external CA in facilitating the availability of CO2 that limits the photosynthesis of microalgae in karst lakes in China.

Variations in the concentrations and isotopic compositions (δ 13 C DIC ) of dissolved inorganic carbon (DIC) reflect contamination and biogeochemical cycling of the carbon in ground water. In order to understand contamination and biogeochemical cycling of DIC, we carried out research on the geochemistry of ground water of Guiyang, the capital city of Guizhou Province, China. Results show that ground water is mainly characterized by SO 4 ·HCO 3 -Ca·Mg and HCO 3 -Ca·Mg chemical compositions. The hydrochemical characteristics of these types of water are mainly controlled by lithology of the aquifers. HCO 3 - is the dominant species of DIC in ground water and has lower concentrations and more negative values of δ 13 C DIC in the high-flow (summer monsoon) season, as compared to the low-flow season. This indicates that DIC is relatively enriched in carbon of biological origin in the high-flow season as compared to the low-flow season and that biological activities are the predominant control on shifts of stable carbon isotope values. The evidence that the δ 13 C DIC values of ground water decrease with increasing concentrations of anthropogenic species shows that the carbon isotopic composition of DIC can be a useful tracer of contamination, in addition to biogeochemical cycling of inorganic carbon in ground water. Results from this study show that ground water is impacted by significant levels of contamination from human activities, especially in the urban areas, as well as the northeast and west suburbs, in Guiyang city, southwest China.

The surface microstructures of three kinds of polymer thin films (ladderlike polypropyl-silsesquioxane, organic nanotube and its supermolecule) are studied by atomic force microscopy (AFM) at room temperature in air. The new information then is used for investigation of the microstructure of the polymer from the statistics data of distribution of the adhesion force on the thin films. The statistics of adhesion force distribution agree well with the morphology of AFM. There is good agreement between the experimental results, the configuration models from molecular mechanics calculation and the designed molecular models. We have successfully prepared the organic nanotube and its supermolecular thin film. The liquid crystal molecule has been inserted into the nanotube to form a supermolecule. The statistics results of distribution of the adhesion force would provide interesting data for correctly defining the microstructure of the polymer thin films. We demonstrate that AFM together with molecular mechanics calculation and statistics of the adhesion force distribution would be a good method for studying the microstructure and properties of new functional materials. Copyright © 2001 John Wiley & Sons, Ltd.

Carbamazepine is a popular drug that has been detected in natural environments, but little is known about its biogeochemical cycling, influencing factors, and eco-environmental effects in aquatic ecosystems. Interaction between carbamazepine and humic substances, including fulvic and humic acids, was studied using three-dimensional excitation-emission matrix fluorescence spectroscopy and synchronous-scan fluorescence spectroscopy. The intrinsic fluorescence of humic substances was quenched on the addition of carbamazepine, and static quenching was the primary mechanism. The binding parameters on their interaction, including the conditional binding constants (log K) and binding capacities (C(L)), were estimated by the Ryan-Weber nonlinear theory equation. Log K ranged from 3.41 to 5.04 L/mol at 25 degrees C and pH 7.0. The influence of pH on the complexation and the competition between carbamazepine and Cu(II) for fluorescence-binding sites also were discussed. The present results would be helpful in understanding the fate and biogeochemical cycling of other pharmaceuticals and personal care products in aquatic ecosystems.