The key role of major and trace elements in the formation of five common urinary stones.

BACKGROUND: Urolithiasis has emerged as a global affliction, recognized as one of the most excruciating medical issues. The elemental composition of stones provides crucial information, aiding in understanding the causes, mechanisms, and individual variations in stone formation. By understanding the interactions between elements in various types of stones and exploring the key role of elements in stone formation, insights are provided for the prevention and treatment of urinary stone disease. METHODS: This study collected urinary stone samples from 80 patients in Beijing. The chemical compositions of urinary stones were identified using an infrared spectrometer. The concentrations of major and trace elements in the urinary stones were determined using Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES) and Inductively Coupled Plasma Mass Spectrometry (ICP-MS), respectively. The data were processed using correlation analysis and Principal Component Analysis (PCA) methods. RESULTS: Urinary stones are categorized into five types: the calcium oxalate (CO) stone, carbonate apatite (CA) stone, uric acid (UA) stone, mixed CO and CA stone, and mixed CO and UA stone. Ca is the predominant element, with an average content ranging from 2.64 to 27.68% across the five stone groups. Based on geochemical analysis, the high-content elements follow this order: Ca > Mg > Na > K > Zn > Sr. Correlation analysis and PCA suggested significant variations in the interactions between elements for different types of urinary stones. Trace elements with charges and ionic structures similar to Ca may substitute for Ca during the process of stone formation, such as Sr and Pb affecting the Ca in most stone types except mixed stone types. Moreover, the Mg, Zn and Ba can substitute for Ca in the mixed stone types, showing element behavior dependents on the stone types. CONCLUSION: This study primarily reveals distinct elemental features associated with five types of urinary stones. Additionally, the analysis of these elements indicates that substitutions of trace elements with charges and ion structures similar to Ca (such as Sr and Pb) impact most stone types. This suggests a dependence of stone composition on elemental behavior. The findings of this study will enhance our ability to address the challenges posed by urinary stones to global health and improve the precision of interventions for individuals with different stone compositions.

Rare earth elements reveal the human health and environmental concerns in the largest tributary of the Mekong river, Northeastern Thailand.

The widespread application of rare earth elements (REEs) in contemporary industries and agriculture, has caused emerging contaminant accumulation in aquatic environments. However, there is a limited scope of risk assessments, particularly in relation to human health associated with REEs. This study investigated the provenance, and contamination levels of REEs, further evaluating their environmental and human health risks in river sediments from an agricultural basin. The concentrations of REEs ranged from 30.5 to 347.7 mg/kg, with showing an upward trend from headwater to downstream. The positive matrix factorization (PMF) model identified natural and anthropogenic input, especially from agricultural activities, as the primary source of REEs in Mun River sediments. The contamination assessment by the geoaccumulation index (I-geo) and pollution load index (PLI) confirmed that almost individual REEs in the samples were slightly to moderately polluted. The potential ecological risk index (PERI) showed mild to moderate risks in Mun River sediment. Regular fertilization poses pollution and ecological risks to agricultural areas, manifesting as an enrichment of light REEs in river sediments. Nevertheless, Monte Carlo simulations estimated the average daily doses of total REEs from sediments to be 0.24 µg/kg/day for adults and 0.95 µg/kg/day for children, comfortably below established human health thresholds. However, the risk of REE exposure appears to be higher in children, and sensitivity analyses suggested that REE concentration contributed more to health risks, whether the adults or children. Thus, concerns regarding REE contamination and risks should be raised considering the wide distribution of agricultural regions, and further attention is warranted to assess the health risks associated with other routes of REE exposure.

Significant influence of urban human activities and marine input on rainwater chemistry in a coastal large city, China.

The coastal urban region is generally considered an atmospheric receptor for terrestrial and marine input materials, and rainfall chemistry can trace the wet scavenging process of these materials. Fast urbanization in China's east coastal areas has greatly altered the rainwater chemistry. However, the chemical variations, determinants, and sources of rainfall are unclear. Therefore, the typical coastal city of Fuzhou was selected for 1-year rainwater sampling and inorganic ions were detected to explore above problems. The findings depicted that rainwater ions in Fuzhou were slightly different from those in other coastal cities. Although NO3-, SO42-, Ca2+ and NH4+ dominated the rainwater ions, the marine input Cl- (22 %) and Na+ (11 %) also contributed a considerable percentage to the rainwater ions. Large differences in ion concentrations (2∼28 times) were found in monthly scale due to the rainfall amount. Both natural and anthropogenic determinants influenced the rainwater ions in coastal cities, such as SO2 emission, air SO2 and PM10 content on rainwater SO42-, NO3-, and Ca2+, and soot & dust emission on rainwater SO42-, NO3-, indicating the vital contribution of human activities. Stoichiometry and positive matrix factorization-based sources identification indicated that atmospheric dust/particles were the primary contributor of Ca2+ (83.3 %) and F- (83.7 %), and considerable contributor of SO42- (39.5 %), NO3- (38.3 %) and K+ (41.5 %). Anthropogenic origins, such as urban waste volatilization and fuel combustion emission, contributed 95 % of NH4+, 54.5 % of NO3- and 41.9 % of SO42-, and the traffic sources contribution was relatively higher than fixed emission sources. The marine input represented the vital source of Cl- (77.7 %), Na+ (84.9 %), and Mg2+ (55.3 %). This work highlights the significant influence of urban human activities and marine input on rainwater chemicals and provides new insight into the material cycle between the atmosphere and earth-surface in coastal city.

Exploration of natural processes and anthropogenic inputs by Zn isotopes in suspended particulate matter: A case study from the Lancang River in Southwest China.

River is an important pathway for the biogeochemical cycle of Zn. This study reports Zn concentration and δ66Zn composition for suspended particulate matter (SPM) from Lancang River basin in Southwest China, and explore the impact of natural processes and human activities on Zn cycle. The SPM samples have a much higher average Zn content (162 mg kg-1) than that of the upper crust (67.0 mg kg-1), but it is close to the value of the Pearl River (187 mg kg-1). The enrichment factor (EF) values of Zn in SPM range from 1.08 to 6.88, with an average of 2.15, which does not show significant pollution characteristics. The δ66Zn values in SPM range from -0.67‰ to +0.63‰, with an average of +0.13‰. The δ66Zn values showed positive correlation with Ca/Mg ratios while showed little correlation with Zn contents in SPM. It indicated that anthropogenic sources have limited influence on SPM, and the Zn isotope composition in SPM is more likely to be inherited from the weathered rocks materials and influenced by natural fractionation processes in river water. This result contributes to understanding of the geochemical cycling process of Zn and its environmental effects in water.

Remarkable contamination characteristics, potential hazards and source apportionment of heavy metals in surface dust of kindergartens in a northern megacity of China.

It is essential to understand the impact of heavy metals (HMs) present in the surface dust (SD) of kindergartens on children, who are highly sensitive to contaminated dust in cities in their growth stage. A study was conducted on 11 types of HMs present in the SD of 73 kindergartens in Beijing. This study aims to assess the pollution levels and sources of eleven HMs in Beijing's kindergartens surface dust (KSD), and estimate the potential health risks in different populations and sources. The results indicate that Cd has the highest contamination in the KSD, followed by Pb, Zn, Ni, Ba, Cr, and Cu. The sources of these pollutants are identified as industrial sources (23.7%), natural sources (22.1%), traffic sources (30.4%), and construction sources (23.9%). Cancer risk is higher in children (4.02E-06) than in adults (8.93E-06). Notably, Cr is the priority pollutant in the KSD, and industrial and construction activities are the main sources of pollution that need to be controlled. The pollution in the central and surrounding areas is primarily caused by historical legacy industrial sites, transportation, urban development, and climate conditions. This work provides guidance to manage the pollution caused by HMs in the KSD of Beijing. ENVIRONMENTAL IMPLICATION: Children within urban populations are particularly sensitive to pollutants present in SD. Prolonged exposure to contaminated SD significantly heightens the likelihood of childhood illnesses. The pollution status and potential health risks of HMs within SD from urban kindergartens are comprehensively investigated. Additionally, the contributions from four primary sources are identified and quantified. Furthermore, a pollution-source-oriented assessment is adopted to clearly distinguish the diverse impacts of different sources on health risks, and the priority pollutants and sources are determined. This work holds pivotal importance for risk management, decision-making, and environmental control concerning HMs in KSD.

Effect of damming on hydrogeochemical characteristics and potential environmental risks in a large reservoir: Insights from different vertical layer sampling.

The water environment of large reservoirs is fragility due to effects from hydrological regulation of damming and anthropogenic inputs. As a critical path to quantify the natural chemical weathering and assess environmental risks, solute chemistry of river has been widely focused on. However, the complexed hydrological conditions of large reservoir affect the chemical compositions, and the significance of solute vertical geochemistry as an indicator of chemical weathering and water quality health remains explore. Therefore, the Three Gorges Reservoir (TGR) was selected as a typical study area, which is the world's largest hydropower project and subject to frequent water quality problems. Then, the chemical compositions in stratified water were determined. Ca2+ (52.8 ± 4.3 mg/L) and HCO3- (180.9 ± 8.9 mg/L) were the most abundant ions among cations and anions, respectively. Incremental mean concentration of total major ions followed with the increase of riverine depth and flow direction. An improved inversion model was used to quantify the source contribution, which weathering of dolomite (34%) and calcite (38%) contributed the most to total cations, and the influences of agriculture and sewage discharge were limited. Additional contributions of evaporite and pyrite oxidation were found in analysis of deeper water samples, which also results in 2%-67% difference in estimated CO2 release flux using data from different depth, indicating additional information about sulfuric acid driven weathering was contained. Finally, the water quality of the reservoir was assessed for irrigation and non-carcinogenic risks. Results showed the stratified water of TGR can be used as a good water source of irrigation. However, NO3- (5.1 ± 1.1 mg/L) may have a potential non-carcinogenic risk to children, especially in surface water. To sum up, this study provided an indispensable supplement to the water chemistry archives in the TGR basin, serving as theoretical references for environmental management of large reservoirs.

Iron isotope fractionation of redox and geochemical cycling in the typical Gleysols in Mun River Basin, Northeast Thailand.

Iron (Fe) isotope is a potential tool for tracking redox process and geochemical cycling in terrestrial environment. In this study, Fe concentration and its isotopic composition (δ56Fe) in two typical Gleysol profiles (M1 and M2) were investigated to distinguish the processes which influence the variation of Fe isotopic composition during redox regimes in the Mun River Basin (MRB). Under oxidizing condition, Fe(II) was oxidized and re-precipitated to form Fe(III) (hydr)oxides zone (Fe nodule-containing zone) in two Gleysol profiles, leading to extremely light Fe isotopes in these zones. The results revealed that the lowest δ56Fe value in Fe(III) (hydr)oxides zone was derived from the migration of light Fe isotopes in upper zone, and Fe(II) was retained and oxidized to Fe(III) (hydr)oxides. Proton-promoted dissolution and leaching were two critical factors leading to a decrease in Fe concentration, which were accompanied by the accumulation of heavy Fe isotopes in the upper zone of M1 profile. In M2 profile, light Fe induced by soil organic matter was accumulated in the topsoil with abundant organic matter. These findings provide comprehensive information of Fe isotopic fractionation and Fe cycling in soil profiles, which would contribute to the understanding of biogeochemical elemental cycling in terrestrial ecosystems.

Agricultural activity on the Mun River basin: insight from spatial distribution and sources of dissolved rare earth elements in northeast Thailand.

Rare earth elements (REE) are emerging pollutants of concern, impacted by intensive fertilizer use and discharge of human and animal waste into agricultural watersheds. However, the natural values and potential anthropogenic enrichment of REE in aqueous systems of the agricultural basins remain poorly understood. This study investigated the spatial variation of dissolved REE in a predominantly agricultural river (Mun River) in northeast Thailand. Dissolved ΣREE concentrations in the Mun River ranged from 5.08 to 272.91 ng/L, with the highest concentrations observed in the middle reaches where agricultural fertilizers and wastewater increased dissolved REE concentrations. The PAAS-normalized patterns and dissolved Eu anomaly jointly reveal that the dissolved ΣREE mainly originated from local rocks and agricultural fertilizers. The dissolved REE in the Mun River is characteristic of a depleted light REE relative to heavy REE, slightly negative Ce anomaly, positive Eu anomaly, and positive Gd anomaly in a punctate distribution. The correlation analysis of (La/Yb)N with fluvial pH and HCO3- indicates that the water environment characteristics of the Mun River control dissolved REE fractionation. The Ce anomaly is associated with the oxidation environment, whereas the Eu anomaly is linked to the lithologic inheritance. Positive punctate Gd anomalies are influenced by human-caused wastewater discharge and applying fertilizers, raising Gd concentrations beyond natural background levels. This study has suggested that the geochemical characteristics of dissolved REE are affected by agricultural disturbances, and future environmental research on dissolved REE is essential to clarifying the impacts of REE on agriculture, the environment, and human health.

Preliminary investigation of soil organic carbon distribution and turnover patterns, and potential pollution sources in and around a typical coking plant in North China.

The variation characteristics of soil organic carbon (SOC) in and around the coking plant area are still unclear. In this work, the concentration and stable carbon isotope composition of SOC in coke plant soils were investigated to preliminarily identify the sources of SOC in and around the plant area, and to characterize soil carbon turnover. Meanwhile, the carbon isotopic technique was used to initially identify the soil pollution processes and sources in and around the coking plant area. The results demonstrate that the SOC content (12.76 mg g-1) of the surface soil in the coking plant is about 6 times higher than that outside the coking plant (2.05 mg g-1), and the variation range of δ13C value of the surface soil in the plant (-24.63～-18.55‰) is larger than that of the soil outside the plant (-24.92～-20.22‰). The SOC concentration decreases gradually from the center of the plant outward with increasing distance, and the δ13C in the middle and north of the plant tends to be positive compared with the δ13C in the west and southeast of the plant. As the increase of soil depth, the SOC content and δ13C value in the plant increases. On the contrary, δ13C value and SOC content outside the plant decreases, with a minor variation. Based on the carbon isotope method, the SOC in and around the coking plant area is mainly from industrial activities (e.g., coal burning and coking), and partly from C3 plants. Notably, organic waste gases containing heavy hydrocarbons, light oils, and organic compounds accumulated in the northern and northeastern areas outside the plant due to south and southwest winds, which may pose an environmental health risk.

Fe contents and isotopes in suspended particulate matter of Lancang River in Southwest China.

Iron (Fe) isotope geochemistry in rivers is crucial for comprehending surficial weathering and geochemical cycle mechanisms. Lancang River is an important channel for material transport between the Tibet Plateau and the oceans of Southeast Asia. In this study, Fe contents and Fe isotope (δ56Fe) compositions in the suspended particulate matter (SPM) are investigated to discuss the rock weathering processes in the Lancang River Basin. The δ56Fe values of SPM range from 0.01 ‰ to 0.21 ‰, with an average of 0.12 ‰, close to the average δ56Fe value of continental crust (0.07 ‰). The results indicate that the fractionation of Fe isotopes is limited caused of weathering process in the Lancang River Basin. Due to the interception of dense dams in the middle and lower reaches (1000-2000 m), the dissolved oxygen (DO) values of river water and the Fe contents of SPM remain at a relatively highest level, whereas the δ56Fe values in SPM are more positive. The positive correlation between chemical index of alteration (CIA) values and the Fe contents suggest that Fe in the tributary SPM may represent the weathering degree of their source areas. The increase of DO in the mainstream water may promote the decomposition and dissolution of SPM, thus increasing the contents of Fe in the remaining SPM, and causing slight positive fractionation of Fe in SPM. This study presents a complete analysis of the Fe isotope's potential utility in identifying the source of SPM. In addition, the Fe isotope may represent some alterations encountered by SPM throughout the runoff process.

Strontium isotope ratios in kidney stones reveal the environmental implications for humans in Beijing, China.

Kidney stones are a common disease that threatens human health on a global scale and are closely related to the contemporary environment. The strontium isotope ratio (87Sr/86Sr) has been widely used to trace the migration of ancient humans through bones and teeth, which recorded their bioavailable Sr from the environment. However, no 87Sr/86Sr data for kidney stones have been reported. Therefore, this study explored the Sr content of kidney stones and reported their 87Sr/86Sr data for the first time to reflect the environmental implications for humans; 66 calcium oxalate kidney stones collected in Beijing were measured for calcium (Ca), magnesium (Mg) and strontium (Sr) content to explore Sr distribution behavior in kidney stones, and 17 samples were tested for strontium isotopes. Ca and Mg had a joint effect on the Sr content of kidney stones, with magnesium having a stronger effect, whereas 87Sr/86Sr values were unaffected by these elements. The 87Sr/86Sr values of kidney stones ranged from 0.709662 to 0.710990, within the range of environmental soil and water in Beijing. Drinking water and surface soils (representing food sources) mainly contributed to the bioavailable Sr of kidney stones, while sea spray and dust storm did not. This study is the first to report 87Sr/86Sr values for kidney stones. Evidence of Sr isotope ratios in kidney stones reveals environmental implications for humans and bioavailable Sr sources, demonstrating a great potential of Sr isotope ratios at the intersection of life and environmental sciences.

Alterations of ecosystem nitrogen status following agricultural land abandonment in the Karst Critical Zone Observatory (KCZO), Southwest China.

Background: Secondary succession after agricultural land abandonment generally affects nitrogen (N) cycle processes and ecosystem N status. However, changes in soil N availability and NO3 - loss potential following secondary succession are not well understood in karst ecosystems. Methods: In the Karst Critical Zone Observatory (KCZO) of Southwest China, croplands, shrub-grass lands, and secondary forest lands were selected to represent the three stages of secondary succession after agricultural land abandonment by using a space-for-time substitution approach. The contents and 15N natural abundance (δ 15N) of leaves, soils, and different-sized aggregates at the three stages of secondary succession were analyzed. The δ 15N compositions of soil organic nitrogen (SON) in aggregates and soil to plant 15N enrichment factor (EF = δ 15Nleaf -δ 15Nsoil), combined with soil inorganic N contents and δ 15N compositions were used to indicate the alterations of soil N availability and NO3 -loss potential following secondary succession. Results: Leaf N content and SON content significantly increased following secondary succession, indicating N accumulation in the soil and plant. The δ 15N values of SON also significantly decreased, mainly affected by plant δ 15N composition and N mineralization. SON content in macro-aggregates and soil NH4 + content significantly increased while δ 15N values of NH4 + decreased, implying increases in SON stabilization and improved soil N availability following secondary succession. Leaf δ 15N values, the EF values, and the (NO3 --N)/(NH4 +-N) ratio gradually decreased, indicating reduced NO3 - loss following secondary succession. Conclusions: Soil N availability improves and NO3 - leaching loss reduces following secondary succession after agricultural land abandonment in the KCZO.

Land-use conversion controls on the mobility of Zn in paddy soils revealed by stable Zn isotopes.

Understanding Zn biogeochemical cycling is necessary for monitoring Zn supply for plants and life during land use conversion, which is critical for environmentally sustainable development. But little is known about how the conversion of paddy soil to abandoned land affects the Zn isotope signature. A comparative field observation was conducted in northeast Thailand to investigate the Zn isotope footprint of paddy soils and abandoned paddy soils (PL and NPL). Our results show that Zn (τZnint : 0.04) slightly retains on PL, but is lost from NPL (τZnint from - 0.81 to - 0.24) to the river during weathering. Compared to PL (Δ66Znparent-soil: -0.29 ‰), more 66Zn isotopes might enter the river when rice cultivation ceases in NPL (Δ66Znparent-soil from -0.26 ‰ to -0.47 ‰). Rice harvest and then root decay might result in heavy 66Zn isotopes accumulating at the topmost soil in PL (δ66Zn: 0.14 ‰) and short-term abandonment (1-2 years) in paddy soils (NPL1 δ66Zn: 0.18 ‰). The release of assimilated Zn, and then the high adsorption of Zn in the Fe-SOM-metal(loid)s ternary system positively contribute to the high [Zn] in PL, while this was not observed in NPL. Our findings provide a comprehensive insight into the Zn isotope signature in response to the conversion of land-use types, which is beneficial for understanding the terrestrial Zn geochemical cycle.

Sources and geochemical behaviors of rare earth elements in suspended particulate matter in a wet-dry tropical river.

The processes of rock weathering and soil erosion, and hydrochemical characteristics are significantly affected by the climate in a basin. However, the sources of rare earth elements (REEs) in suspended particulate matter (SPM) under soil erosion, as well as the geochemical behaviors of REEs with changes in hydrochemical properties between seasons, have received little attention in the tropical monsoon zone. In this study, the temporal and spatial characteristics of the REEs in SPM were investigated in the Mun River (a wet-dry tropical river), Northeast Thailand. During the dry season, the compositions of the major elements and REEs in SPM were very similar to those in local soils. However, there was a clear difference between the compositions of these major elements and REEs in SPM and those in local soils during the rainy season. This suggests that the SPM and its REEs during the dry season were primarily derived from soil materials, while those during the rainy season were primarily derived from soil materials and products of rock weathering. The ∑REE contents in SPM decreased from 191.2 mg kg-1 to 170.6 mg kg-1 along the flow direction during the dry season, while they increased from 100.7 mg kg-1 to 135.3 mg kg-1 during the rainy season. The δEu (mean 1.26) and δGd (mean 1.58) values in SPM during the rainy season were higher than those (mean δEu 1.21 and mean δGd 1.12) during the dry season, and both of them were mainly controlled by the relative contributions of rock weathering products and soil materials to SPM. The results suggest that the temporal differences of REE geochemical characteristics in SPM were closely associated with SPM sources, while their spatial variations were mainly affected by the water-particle interaction in the tropical monsoon zone.

Nitrate dynamics and source identification of rainwater in Beijing during rainy season: Insight from dual isotopes and Bayesian model.

Anthropogenic reactive nitrogen emissions have a significant impact on atmospheric chemical composition and earth surface ecosystem. As one of the most important sinks of atmospheric nitrogen, the wet deposition of nitrate (rainwater NO3-) has been widely concerned. Yet, the sources and transformation processes of wet deposited NO3- were not well revealed in megacity during rainy season in the context of global climate change. Here, we investigated the concentrations of nitrogen components and dual isotopes of rainwater nitrate collected in Beijing during July to August 2021 (rainy season). The main findings showed that the concentrations of NH4+-N, NO3--N, and NO2--N ranged 0.5- 6.7 mg L-1, 0.3- 4.5 mg L-1, and 0.05- 0.18 mg L-1, respectively, with the average relative percentages of 69 %, 29 %, and 2 %. The stoichiometry analysis of characteristic ion ratios indicated that the contribution of municipal wastes and agricultural sources to rainwater NH4+-N is relatively significant, while traffics were the major contributor of NO3--N instead of the fixed emission. Rainwater δ15N-NO3- and δ18O-NO3- presented slightly 15N-depleted characteristic compared to previous studies with the average values of -3.9 ± 3.1 ‰ and 58.7 ± 12.6 ‰. These isotope compositions suggesting an origin of rainwater NO3- from the mixing of multi-sources and was mainly generated via the pathway of OH radical oxidization. Further source apportionment of rainwater NO3- by Bayesian mixing model evaluated that traffic (30.3 %) and soil (30.3 %) emissions contributed mostly to NO3-, while the contribution of biomass burning (18.8 %) and coal combustion (20.6 %) were relatively lower. This study highlighted the important role of dual isotopes in rainwater nitrate source identification and formation processes in megacity.

Calcium isotope ratio in kidney stones: preliminary exploration of mechanism from the geochemical perspective.

Stable calcium (Ca) isotope ratios are sensitive and radiation-free biomarkers in monitoring biological processes in human bodies. Recently, the Ca isotope ratios of bone, blood, and urine have been widely reported to study bone mineral balance. However, as a pure Ca crystallization product, there is no report on the Ca isotope ratios of kidney stones, even though the prevalence of kidney stones is currently on the rise. Here, we measured Ca isotope data of 21 kidney stone samples collected in Beijing, China. The δ44/42CaNIST 915a values ranged from 0.25‰ to 2.85‰ for calcium oxalate, and from 0.38‰ to 3.00‰ and 0.61‰ to 0.69‰ for carbonate apatite and uric acid, respectively. Kidney stones have heavier Ca isotope ratios than bone or blood, which is probably because complexed Ca contains more heavy Ca isotopes than free Ca2+. Ca isotope evidence suggests that magnesium (Mg) affects kidney stone formation, as the δ44/42CaNIST 915a value is inversely correlated with the Ca/Mg ratio. This study provides important preliminary reference values on the Ca isotopic composition of kidney stones and proposes a factor influencing Ca isotope fractionation in biological processes for future research.

Environmental implications of land use change on the fate of Zn in agricultural soils: A case study of Puding karst soils, southwest China.

Land use change threatens food security because it may cause the depletion and/or low bioavailability of micronutrients in agricultural soils. Therefore, it is significant to investigate the fate of micronutrients and predict the potential environmental problems. The zinc isotope technique is of particular interest in interpreting soil processes. In this study, Zn isotopic data of soil samples in five profiles based on different land uses were provided, and Zn behavior in different soils was discussed. The isotopic ratios of soil samples in the abandoned orchard, secondary forest, abandoned cropland, and cropland are similar, with the δ66Zn varying from 0.15 to 0.29‰. However, the samples in shrub grassland show a lower δ66Zn of 0-0.20‰, which may be affected by anthropogenic sources. For the vertical patterns, the non-cultivated long-rooted plants (i.e., abandoned orchard and secondary forest) show no significant difference in the distribution of δ66Zn, but the patterns of cropland and abandoned cropland samples are reversed. The cropland samples show positive correlations between δ66Zn and Fe2O3 (R2 = 0.90) and MnO (R2 = 0.75), indicating that Fe and Mn oxides preferentially adsorb heavy Zn isotopes on the mineral surfaces. The high affinity between Zn and oxides indicated that the concentration of bio-available Zn in cropland soils was getting lower. As a result, the supplies of micronutrients may be deficient and urged from fertilizer. This study provides a better understanding of Zn cycling in agricultural systems and gives improvements in soil management.

Effects of high Ca and Mg stress on plants water use efficiency in a Karst ecosystem.

Background: Karst ecosystems are widely distributed in the world, with one of the largest continuous Karst landforms in Southwest China. Karst regions are characterized by water shortage, high soil calcium (Ca) and magnesium (Mg) content, and soil nutrient leaching, resulting in drought stress and growth limitation of plants. Methods: This study compared nitrogen (N), phosphorus (P), potassium (K), Ca, and Mg of herbaceous and woody plants in a small Karst ecosystem in Southwest China. The indexes of water use efficiency (WUE) were calculated to identify the drought stress of plants in this Karst ecosystem. Meanwhile, the relationship between Ca and Mg accumulation and WUE was evaluated in herbaceous and woody plants. Results: Herbaceous plants showed a higher content of leaf N (13.4 to 40.1 g·kg-1), leaf P (2.2 to 4.8 g·kg-1) and leaf K (14.6 to 35.5 g·kg-1) than woody plants (N: 10.4 g to 22.4 g·kg-1; P: 0.4 to 2.3 g·kg-1; K: 5.7 to 15.5 g·kg-1). Herbaceous plants showed a significantly positive correlation between WUE and K:Ca ratio (R = 0.79), while WUE has a strongly positive correlation with K:Mg ratio in woody plants (R = 0.63). Conclusion: Herbaceous plants suffered from nitrogen (N) limitation, and woody plants were constrained by P or N+P content. Herbaceous plants had higher leaf N, P, and K than woody plants, while Ca and Mg showed no significant differences, probably resulting from the Karst environment of high Ca and Mg contents. Under high Karst Ca and Mg stress, herbaceous and woody plants responded differently to Ca and Mg stress, respectively. WUE of herbaceous plants is more sensitive to Ca stress, while that of woody plants is more sensitive to Mg stress. These findings establish a link between plant nutrients and hydraulic processes in a unique Karst ecosystem, further facilitating studies of the nutrient-water cycling system in the ecosystem.

The Impacts of Nitrogen Pollution and Urbanization on the Carbon Dioxide Emission from Sewage-Draining River Networks.

Carbon dioxide (CO2) emissions from river water have sparked worldwide concerns due to supersaturate CO2 levels in the majority of global rivers, while the knowledge on the associations among nitrogen pollution, urbanization, and CO2 emissions is still limited. In this study, the CO2 partial pressure (pCO2), carbon and nitrogen species, and water parameters in sewage-draining river networks were investigated. Extremely high pCO2 levels were observed in sewage and drainage river waters, such as Longfeng River, Beijing-drainage River, and Beitang-drainage River, which were approximately 4 times higher than the averaged pCO2 in worldwide rivers. Correlations of carbon/nitrogen species and pCO2 indicated that carbon dioxide in rural rivers and sewage waters primarily originated from soil aeration zones and biological processes of organic carbon/nitrogen input from drainage waters, while that in urban rivers and lakes was mainly dominated by organic matter degradation and biological respiration. Enhanced internal primary productivity played critical roles in absorbing CO2 by photosynthesis in some unsaturated pCO2 sampling sites. Additionally, higher pCO2 levels have been observed with higher NH4+-N and lower DO. CO2 fluxes in sewage waters exhibited extremely high levels compared with those of natural rivers. The results could provide implications for assessing CO2 emissions in diverse waters and fulfilling water management polices when considering water contamination under intense anthropogenic activities.

Zn isotope fractionation in laterites from Yunnan province, southwest China: Implications for the Zn cycles and its environmental impacts in (sub-) tropics.

The weathering and development of laterites can influence trace element cycling in (sub-) tropics. Zinc (Zn) is a ubiquitous trace metal that involves both abiotic and biotic processes in soils. To explore Zn behavior in laterites, Zn cycling in (sub-) tropics, and the environmental impacts, Zn isotope systematics were presented for two laterite profiles from Yunnan province, southwest China. The laterite samples exhibit the δ66Zn of 0.02 ‰-0.56 ‰, indicating a light shift of Zn isotope ratios (Δ66Znlaterite-parent rock = -0.47 ‰-0.07 ‰) relative to bulk parent granite. This observation is attributed to the preferential preservation of light Zn isotopes on the surface of secondary Fe oxides. As a result, laterites are likely to control the instantaneous riverine δ66Zn in (sub-) tropical regions heavier than unweathered rocks. The isotopic signature of different vegetation covered soils show that shrub-covered soils are stronger leached (average τZn = -0.61) and have a smaller Δ66Znlaterite-parent rock (=-0.15 ‰), relative to forest-covered soils (=-0.20 ‰). Due to the strong loss of Zn (average τZn = -0.61 to -0.12) and large amounts of low-bioavailable Zn preserved in oxides, the micronutrient supplies for plant growth are difficult to maintain and need more fertilization. This study is helpful for a better understanding of global Zn cycling and the management of micronutrients in (sub-) tropical soil-plant systems.