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Anthropogenic input of sulfate (SO

Exotic plant invasion is an urgent issue occurring in the biosphere, which can be stimulated by environmental nitrogen (N) loading. However, the allocation and assimilation of soil N sources between leaves and roots remain unclear for plants in invaded ecosystems, which hampers the understanding of mechanisms behind the expansion of invasive plants and the co-existence of native plants. This work established a new framework to use N concentrations and isotopes of soils, roots, and leaves to quantitatively decipher intra-plant N allocation and assimilation among plant species under no invasion and under the invasion of Chromolaena odorata and Ageratina adenophora in a tropical ecosystem of SW China. We found that the assimilation of N derived from both soil ammonium (NH4+) and nitrate (NO3-) were higher in leaves than in roots for invasive plants, leading to higher leaf N levels than native plants. Compared with the same species under no invasion, most native plants under invasion showed higher N concentrations and NH4+ assimilations in both leaves and roots, and increases in leaf N were higher than in root N for native plants under invasion. These results inform that preferential N allocation, dominated by NH4+-derived N, to leaves over roots as an important N-use strategy for plant invasion and co-existence in the studied tropical ecosystem.

Understanding of the binding characteristics of wetland dissolved organic matter (DOM) and different metals is important for the quantitative assessment of the environmental behavior of metals in wetlands. In this study, different types of spectroscopy including ultraviolet-visible absorption, Fourier transform infrared, and fluorescence spectroscopy was used to investigate the binding characteristics of Fe

Sulfur (S) dynamics in soils formed from granite remain poorly understood despite its importance as an essential plant macronutrient and component of soil organic matter. We used stable S isotope ratios to trace the sources and biogeochemical processes of S in four forest soil profiles developed on granite under contrasting climate conditions. The soil S is derived mainly from decomposing litter; no significant geogenic contribution to its content is noted as a result of the low S concentration of the granite (~ 5 μg/g). Colder/drier climate results in high organic S retention at the surface due to weak mineralization of organic S. Although warmer/wetter climate increases the S mineralization and leaching loss, SO42− adsorption is an important S retention process in the subsurface. The vertical distribution of S isotope compositions in the soil profiles across the four sites indicates (i) a downward increase in δ34S values in the upper profiles due to continuous mineralization of organic S with an occasional decrease in δ34S values in the subsurface due to dissimilatory sulfate reduction (DSR), (ii) constantly high δ34S values in the middle profiles due to the low water permeability, and (iii) a downward decrease in δ34S values in the low profiles due to increased contribution of bedrock with depth. Regardless of the variation in soil depth and climate, the total S concentration is proportional to the pedogenic Fe/Al minerals, suggesting the important role of secondary Fe/Al minerals in retaining S in soils. This study provides an integration and synthesis of controls of climatic and edaphic variables on S dynamics in forest soil profiles developed on granite.

Carbon (C) cycling and phytoplankton community succession are very important for hydropower reservoir ecosystems; however, whether the former controls the latter or the reverse is still debated. To understand this process, we investigated phytoplankton species compositions, stable C isotope compositions of dissolved inorganic C and particulate organic C (δ13C-DIC and δ13C-POC), and related environmental factors in seven hydropower reservoirs on the Wujiang River, Southwest China. A total of 36 algal genera from seven phyla were identified, and phytoplankton community exhibited obvious temporal and spatial difference. The δ13C-DIC (from -9.96 to -3.73‰) and δ13C-POC (from -33.44 to -21.17‰) co-varied with the algal species succession and increased markedly during the shift of dominant species from Bacillariophyta to Pyrrophyta or Cyanophyta. In addition, the strong C fixation in the euphotic layer resulted in great δ13C-DIC and CO2 stratification in the reservoir profile. Statistical analyses and C isotope evidence demonstrate that an increase in water temperature triggers phytoplankton community succession, and that CO2 availability is a key to drive the succession direction, and in turn, C cycling is enhanced when phytoplankton are dominated by Pyrrophyta or Cyanophyta in hydropower reservoirs. This study confirms that C cycling and phytoplankton community succession interact with each other and evolve synchronously, and will be helpful to systematically evaluate the environmental consequences of river damming.Keywords: Carbon biogeochemical cycling; Phytoplankton community succession; Stable carbon isotope; Reservoir effect; Wujiang River.

Lignin is a highly complex, plant-derived natural biomass component, the analysis of which requires significant demands on the analytical platform. Fourier transform ion cyclotron mass spectrometry (FT-ICR MS) has been shown to be able to readily assess the complexity of lignin and lignin degradation products by assigning tens of thousands of compounds with elemental formulae. Nevertheless, many experimental and instrumental parameters introduce discrimination towards certain components, which limits the comprehensive MS analysis. As a result, a complete characterization of the lignome remains a challenge. The present study investigated a degraded lignin sample using FT-ICR MS and compared several atmospheric pressure ionization methods, e.g., electrospray ionization, atmospheric-pressure chemical ionization, and atmospheric-pressure photoionization. The results clearly show that the number of heteroatoms (e.g., N, S, P) in the sample greatly increases the chemical diversity of lignin, while at the same time also providing potentially useful biomarkers. We demonstrate here that FT-ICR MS was able to directly isolate isotopically pure single components from the ultra-complex mixture for subsequent structural analysis, without the time-consuming chromatographic separation. CAPSULE: Various ionization techniques coupled to FT-ICR MS provide a powerful tool to assess the lignome coverage.

Straw return is becoming a routine practice in disposing of crop residues worldwide. However, the potential effect of such operation on the chemistry of local groundwater is not well documented. Here, shallow groundwater in an area where wheat-maize straw return is practiced was analyzed, and the seasonal changes in the nitrate concentration and the isotope compositions of NO3- and H2O were determined along two flow paths. Measured δD and δ18O in waters indicated that the groundwater was mainly recharged by atmospheric precipitation, while measured δ15N and δ18O in nitrate suggested that the sources for groundwater NO3- included urea fertilizer, soil nitrogen, and sewage/manure. Reduced NO3- concentrations coincided with an enrichment of organic matter in the groundwater of the straw return area, revealing an environmental condition that facilitates nitrate reduction, whereas increased δ15N-NO3- and δ18O-NO3- along the flow path suggested the occurrence of denitrification. Further analyses showed that, compared to the cases in the absence of straw return, as much as 80% and 90% of groundwater nitrate was removed in low and high water seasons in the straw return area, pointing to a potential positive effect of straw return to groundwater quality.

Soils, vegetables and rainwaters from three vegetable production bases in the Guiyang area, southwest China, were analyzed for Pb concentrations and isotope compositions to trace its sources in the vegetables and soils. Lead isotopic compositions were not distinguishable between yellow soils and calcareous soils, but distinguishable among sampling sites. The highest (207)Pb/(206)Pb and (208)Pb/(206)Pb ratios were found for rainwaters (0.8547-0.8593 and 2.098-2.109, respectively), and the lowest for soils (0.7173-0.8246 and 1.766-2.048, respectively). The (207)Pb/(206)Pb and (208)Pb/(206)Pb ratios increased in vegetables in the order of rootsstemsleavesfruits. Plots of the (207)Pb/(206)Pb ratios versus the (208)Pb/(206)Pb ratios from all samples formed a straight line and supported a binary end-member mixing model for Pb in vegetables. Using deep soils and rainwaters as geogenic and anthropogenic end members in the mixing model, it was estimated that atmospheric Pb contributed 30-77% to total Pb for vegetable roots, 43-71% for stems, 72-85% for leaves, and 90% for capsicum fruits, whereas 10-70% of Pb in all vegetable parts was derived from soils. This research supports that heavy metal contamination in vegetables can result mainly from atmospheric deposition, and Pb isotope technique is useful for tracing the sources of Pb contamination in vegetables.

Sulfur source identification previously reported has been based on sulfur isotopic ratios in either rainwater or mosses. The δ 34 S values of rainwater sulfate and the epilithic moss Haplocladium microphyllum in Nanchang region (China) were determined for comparisons and used to delineate atmospheric sulfur sources. At the urban and rural sites, similar mean δ 34 S values were observed between rainwater sulfate (+ 1.6‰ and − 0.2‰, respectively) and epilithic mosses (+ 1.7‰ and + 0.6‰, respectively), suggesting that mosses acquire δ 34 S values similar to those found for rainwater sulfate. This has further demonstrated that moss δ 34 S signatures hold valuable source-specific information as rainwater δ 34 S values do. The δ 34 S values of both rainwater sulfate and epilithic mosses indicated that atmospheric sulfur in Nanchang region was mainly associated with coal combustion. The lower δ 34 S values at the rural site can be explained by higher contribution of local coals (lower δ 34 S values relative to those of north Chinese coals) and biogenic sulfur.

Dechlorination of chlorinated aromatic pollutants (CAPs) has become a major issue in recent decades. This paper reported a theoretical indicator for predicting the reductive dechlorination pathways of polychlorinated dibenzo- p -dioxins (PCDDs), chlorobenzenes and chlorophenols transformed by Dehalococcoides sp. strain CBDB1. Density functional theory (DFT) calculations were carried out at the B3LYP/6-31G(d) level for all related CAPs and Mulliken atomic charges on chlorine atoms ( Q Cl( n ) ) were adopted as the probe of the dechlorination reaction activity. Q Cl( n ) can consistently indicate the main dechlorination daughter products of PCDDs, chlorobenzenes and chlorophenols conducted by strain CBDB1. The dechlorination reaction favors elimination of the chlorine atoms having greater Q Cl( n ) values. The chlorine atom with the greatest Q Cl( n ) value tends preferentially to be eliminated, whereas the chlorine atom with the smallest Q Cl( n ) value tends unlikely to be eliminated or does not react at all. For a series of compounds having similar structure, the maximal Q Cl( n ) of each molecular can be used to predict the possibility of its daughter product(s). In addition, the difference (∆ Q Cl( n ) ) between the maximal Q Cl( n ) and the next maximal Q Cl( n ) of the same molecule can be used to assess the possibility of formation of multiple dechlorination products.

Twenty-two rainwater samples from Guiyang city, southwestern China, have been analyzed for their chemical compositions and 87 Sr / 86 Sr ratios, with a main purpose to get a better understanding of the general features of rainwater in Guiyang city and their correspondences to human activities. The rainwaters studied are almost acidic (pH = 4.53) and show big changes in major ion composition. Ca 2+ and Mg 2+ are the principal cations in the rainwaters and their mean values are 56.6 μmol/L (12.5–163.8 μmol/L) and 12.8 μmol/L (4.5–47.3 μmol/L ), respectively. The sum of Ca 2+ and Mg 2+ accounts for 78%–96% of the total cations in the studied rainwaters. Na + was the least abundant of the major cations with a mean content of 4 μmol/L (0.9–7.8 μmol/L). SO 4 2− is the predominant anion, with a mean content of 94 μmol/L (33.5–279.4 μmol/L), coming next is NO 3 − with a mean content of 48 μmol/L (2.1–251.8 μmol/L). SO 4 2− and NO 3 − together account for 77%–99% of the total anions. Ca 2+ and Mg 2+ in the rainwater are most likely from dissolution of carbonate minerals in dust or aerosol, unlike K + that shows more contribution of anthropogenic sources to the rainwater. Na + does not vary in concentration with Cl − . Significant enrichment of Cl − relative to Na + as compared with sea water indicates negligible contribution of marine source, which is supported by the evidence that the total rainwater samples show lower 87 Sr / 86 Sr ratios (ranging from 0.707934 to 0.709080) than sea water. The rainwater samples are characterized by high contents of NO 3 − , SO 4 2− , and Cl − relative to Na + , as compared to the rainwater from other areas in the world, suggesting that the anions (NO 3 − , SO 4 2− , and Cl − ) have mainly of anthropogenic sources. Sr isotope shows potential to trace sources of contaminants when combined with other chemical factors: covariation of 87 Sr / 86 Sr ratio with Cl − / Na + in the rainwater suggest presence of at least two anthropogenic sources for the rainwater samples studied. The coal-combustion industries are probably the major atmospheric contaminant sources in Guiyang city.

Thallium (Tl) contamination in soils poses a significant threat to human health due to the high toxicity of Tl and its ready assimilation by crops. This study is focused on high concentrations of Tl in soils in the Lanmuchang area of southwest Guizhou, China, which is related to natural processes of Tl-rich sulfide mineralization. Thallium contents range from 40 to 124 mg/kg in soils originating from the mining area, from 20 to 28 mg/kg in slope wash materials, from 14 to 62 mg/kg in alluvial deposits downstream, from 1.5 to 6.9 mg/kg in undisturbed natural soils and0.2 to 0.5 mg/kg Tl in soils from the background area. These values indicate that both the erosion of natural soils from the Tl mineralized area and the mining activity are responsible for the distribution of high Tl concentrations in soils. Two other important toxic metals of interest, mercury and arsenic, also show high contents in soils, and are generally higher than Tl concentrations. Thallium concentration in plants exhibit species-dependent preferences. Thus, the enrichment of Tl in the edible parts of crop species decreases in the following order: green cabbagecarrotchiliChinese cabbagericecorn. The highest level of Tl in green cabbage is up to 500 mg/kg as dry wt., surpassing the values of Tl in the soils in which the green cabbages grow. In contrast, Hg and As are relatively less concentrated in local plants. The average daily uptake of Tl by the villagers of the Lanmuchang area through consumption of locally planted crops has been estimated to be 1.9 mg/person, which is 50 times the daily ingestion of individuals from the Tl-free background area. The daily ingestion of As and Hg from the study area are 0.03 and 0.01 mg, respectively. This indicates that Tl in the contaminated soils related to the natural Tl mineralization is being readily transferred to the human body through the food chain, and poses a significant threat to the health of the local villagers. Arsenic may pose a lesser health hazard, but mercury has an insignificant health risk. This study illustrates a real environmental concern related to land use and human health in areas containing high contents of Tl in soils associated with the natural occurrence of Tl-rich sulfides and coals, with or without mining activities. Thallium contamination in soils should be a critical parameter for proper land use and health related environmental planning and regulations.