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Metal stable isotopes in marine carbonates have been widely used as novel proxies for metal cycling through the geological past. Amongst these metals, copper (Cu) and zinc (Zn) have received great attention owing to their vital roles in metabolic processes. However, whether modern marine biogenic carbonates record the seawater isotope signatures of Cu (δ65Cu) and Zn (δ66Zn) and mechanisms and factors controlling isotope fractionation of these metals remain unclear, hindering applications of both isotope systems in paleoceanography. Here we present annually-resolved records of δ65Cu and δ66Zn in seven coral (Porites) cores sampled from different marine settings in the South China Sea and the Luzon Strait, western Pacific. We find that the aragonitic skeletons of corals are enriched in light Cu but heavy Zn isotopes relative to surface seawaters, with δ65Cu and δ66Zn in the range of −0.16 ± 0.06‰ to 0.40 ± 0.05‰ and 0.06 ± 0.04‰ to 0.46 ± 0.08‰ (2SD), respectively. The coral δ65Cu exhibits significant inter- and intra-colony variations, which are most likely controlled by Rayleigh-type fractionation in the calcifying fluids of corals rather than by changes in environmental factors or seawater δ65Cu. We thus suggest that δ65Cu in ancient carbonates may not be a direct record of Cu isotope compositions in coeval seawaters. In contrast, coral δ66Zn shows insignificant temporal variation, and the Zn isotope fractionation between individual corals and seawaters are relatively small and constant (0.10 ± 0.05‰, n = 33, 2SD). This limited Zn isotope fractionation is much lower than that determined during inorganic precipitation of calcite, which is likely due to pH up-regulation by the coral that changes aqueous Zn speciation, and preferential organic complexation of the heavy Zn isotopes in the calcifying fluids. Therefore, Porites corals are promising archives for tracking historical changes of surface seawater δ66Zn. Our new datasets of reef carbonates, particularly the coral δ65Cu values which are measured for the first time, could provide a better constrain on marine Cu and Zn geochemistry and their modern oceanic mass and isotope budgets.

Phosphorus (P) availability in soils controls critical functions and properties of terrestrial ecosystems. Vertical distribution patterns of P concentration and speciation in soil profiles provide historical records of how pedogenic processes redistribute and transform P and thus change its availability in soils, which, however, remain poorly understood. We determined the patterns in three forest soil profiles of contrasting climate, using fine sampling intervals, P K-edge X-ray absorption near edge (XANES) spectroscopy and chemical extractions. The major features of the patterns persist under the contrasting climate. The total P concentration decreases from A to B horizons, reaches a minimum in the B horizons, and then increases towards the upper C horizons, but with little variations with depth in the lower C horizons. Both calcium-bound inorganic P (Ca–Pi) and organic P (Po) decrease and Fe- and Al-bound Pi [(Fe + Al)–Pi] increases in proportion downward in the A horizons because dust inputs and accumulation of organic matter both decline with increasing depth. Ca–Pi is negligible and (Fe + Al)–Pi is dominant in the B horizons due to strong weathering. There is a strong downward increase in Ca–Pi proportion and decrease in (Fe + Al)–Pi proportion from the lower B to the upper C horizons. New Ca–Pi seems to form in the upper C horizons where downward leaching Ca2+ and phosphate accumulate due to the low water permeability of the soils. In the lower C horizons, Ca–Pi increases and (Fe + Al)–Pi decreases with increasing depth due to decreasing chemical weathering. Regarding P bioavailability, the proportion of occluded P (Pocc) shows an increasing and decreasing trend with increasing depth, being the highest in the B horizons; however, there are no consistent trends for non-occluded P (Pn-occ). While the P vertical patterns can be understood by considering the relative importance of different pedogenic processes, climate affects the intensities of these processes and thus the details of the patterns. When depth-integrated, warmer/wetter climate results in decreases in the proportions of both Ca–Pi and Pn-occ but increases in the P loss and the proportions of Po, (Fe + Al)–Pi, and Pocc. Regardless of soil depth and climate, the Pi speciation, i.e., the relative proportions of Ca–Pi and (Fe + Al)–Pi over total Pi, correlates well with soil pH and weathering degree (Chemical Index of Alteration, CIA), and the Po concentration correlates with pedogenic Fe and Al and organic carbon concentration. The correlations suggest that the Pi speciation is primarily controlled by soil geochemistry/mineralogy, and the Po concentration by both soil geochemistry/mineralogy and biological activities. Pocc correlates with CIA, and thus is mainly controlled by soil mineralogy; but Pn-occ correlates weakly with soil properties, probably due to its susceptibility to combined influences of dust inputs, leaching, biological activities, and adsorption on minerals. The above quantitative relationships may help predict P speciation and availability in diverse soils. We further show that soil profiles, and climate and CIA gradients are useful tools for studying P transformations, particularly for the Pi pool, during pedogenesis. This study provides an integration and synthesis of controls of climatic and edaphic variables on P dynamics in forest soils.

Tectonically active high relief areas are proposed to have a substantial impact on climate regulation throughout the Cenozoic. Here, we present lithium (Li) isotope data of the dissolved load and suspended particulate material from the basins of the Yalong River and the Jinsha River, which drain the high-relief borders of the eastern Tibetan Plateau and constitute the headwaters of the Yangtze River. Dissolved δ7Li values are relatively low and constant in the Jinsha River mainstream (+6.8‰ to +9.7‰) compared to the higher and downstream increasing values in the Yalong River mainstream (+10.8‰ to +17.5‰). Furthermore, dissolved δ7Li values in the major tributaries of the Jinsha and Yalong River are highly variable and increase downstream from +11.4‰ to +29.4‰ and from +9.0‰ to +23.6‰, respectively. Robust correlations between Li, Na, and Cl concentrations identify that evaporite dissolution in the uppermost headwaters of the Jinsha River basin controls the Li budget and riverine δ7Li values of the mainstream and has a significant impact on dissolved Li in the Yangtze River. In contrast to the Jinsha River mainstream, dissolved Li in the Yalong River mainstream and the Jinsha and Yalong River tributaries are dominantly derived from the dissolution of silicates. δ7Li variations in the Yalong River basin and the Jinsha tributaries reflect little Li uptake by clays in the upper reaches and more Li uptake by clays in the lower reaches of the river basins. SWR/D ratios (where SWR is the chemical silicate weathering rate, and D is the total denudation rate) highlight an intermediate silicate weathering intensity under a kinetically limited weathering regime for the study area. However, positive correlations between dissolved δ7Li value and silicate weathering intensity proxies (such as Si/(Nasil + K) and K/(Nasil + K)) indicate an increasing weathering intensity downstream. A positive correlation between dissolved δ7Li values and the annual precipitation and a negative one between δ7Li values and elevation indicates that larger annual precipitation under a flattening relief results in a stronger silicate weathering intensity, thus, more Li uptake in clays and higher riverine δ7Li values in the lower reaches. Compared to the lower reaches of Yangtze River basin (∼+20‰), lower dissolved δ7Li values in its headwater of this study suggest that the increase in δ7Li of seawater over the Cenozoic is influenced by weathering in floodplains that developed due to erosion of high mountains, rather than weathering of mountain belts itself. Combined with silicate weathering rates of the eastern border of the Tibetan Plateau, the highest riverine δ7Li values in its catchments come along with the highest silicate weathering rates and high CO2 consumption, suggesting that a more elevated topography may have an important role in the drawdown of CO2 during the Cenozoic.

To characterize secondary organic aerosols (SOA) over the Tianjin region, we studied the SOA tracers derived from isoprene, α/β-pinene, β-caryophyllene, and aromatics in PM2.5 collected at an urban...

Molecular compositions and stable carbon isotope ratios (δ13C) of n-alkanes and fatty acids (FA) were investigated in urban aerosols from Beijing, China. Seasonal trends for n-alkanes showed a high...

This study aims to clarify the relationship between chemical weathering of rocks and the carbon budget of rivers and better understand the weathering mechanisms of plateau watersheds. We chose to study the Jinsha River, which originates from the Tibetan Plateau and also is in the upper reaches of the Changjiang River. Analysis of hydrochemistry, radiogenic strontium isotope and stable calcium isotopes were conducted of the Jinsha River water samples, which were collected along its mainstream and main tributaries in the summer. The results show that the water chemistry of the mainstream waters is dominated by evaporite weathering, which have low 87Sr/86Sr values (0.7098–0.7108) and wide range of Sr contents (2.70–9.35 μmol/L). In contrast, tributaries of the Jinsha River have higher 87Sr/86Sr (0.7090–0.7157) and lower Sr contents (∼1 μmol/L). Moreover, the Ca isotopic compositions in the mainstream (0.87–1.11‰) are heavier than the tributaries (0.68–0.88‰) and could not be fully explained by the conventional mixing of different sources. We suggest that secondary carbonate precipitation fractionates Ca isotopes in the Jinsha River, and fractionation factors are between 0.99935 and 0.99963. At least 66% of Ca was removed in the mainstream of the Jinsha River through secondary mineral precipitation, and the average value is ∼35% in the tributaries. The results highlight that evaporite weathering results in more carbonate precipitation influencing Ca transportation and cycling in the riverine system constrained by stable Ca isotopic compositions and water chemistry.

Exploring the relationship between weathering and erosion is essential for understanding the evolution of landscapes and formation of soil under the influence of climate, tectonics, and topography. We measured the bulk chemistry of regoliths and calculated their weathering rates and intensity in three locations in China: Inner Mongolia in the mid-temperate semi-humid zone; Jiangxi Province, in the mid-subtropical humid zone; and Hainan Province, in the tropical humid zone. These profiles exhibited increased weathering with increasing temperature and precipitation. The low-gradient profile exhibited stronger weathering of saprolite than of soil, whereas the high-gradient profile showed a more constant weathering pattern. The regolith in the cold climate was the product of easily weatherable minerals, whereas weathering of K-feldspar and even secondary minerals occurred in hot and humid climates. The weathering of subtropical profiles was both supply- and kinetic-limited, controlled by weathering and erosion. The tropical profile experienced supply-limited weathering, indicating slow erosion and an intense weathering profile; the mid-temperate profile was not classifiable due to weak erosion and weathering. Long-term weathering fluxes of these profiles show that Si, Na, and K (or Mg) represent the bulk of the mass lost through weathering. This study underscores that weathering of granitic regolith is controlled by both climatic conditions and landscape.

Extensional rift systems provide important pathways for the release of large amounts of deeply-sourced CO2 into the atmosphere. Continental rifting zones (e.g., East African rift) are thus invoked to be important for understanding the links between CO2 outgassing and global climate change associated with continental breakup. However, deeply-sourced CO2 emissions from extensional rift systems in continental collision zones remain poorly understood. Here, we focus on hydrothermal CO2 emissions from the southern segment of the Yadong-Gulu rift (YGR), the largest extensional rift in southern Tibetan Plateau, aiming at delineating rift-related CO2 emissions from the India-Asia continental collision zone. In-situ measurements of diffuse soil CO2 emissions indicate that average soil CO2 fluxes from the Kangbu, Mengzha, and Chaduo hydrothermal fields are 40, 700, and 255 g m−2 d−1, respectively. Combined with average soil CO2 fluxes (20–437 g m−2 d−1) from central and northern YGR, we speculate a relatively steady-state CO2 degassing pattern for the entire rift. The magnitude of soil CO2 fluxes of the YGR is higher than that of representative areas of the East African rift system. Evidence from 3He/4He reveals a pure crustal origin for CO2-bearing fluids in southern YGR, while the involvement of mantle CO2 is recognized in the central and northern rift segments. We suggest that metamorphic decarbonation of crustal rocks at variable depths is the primary cause for CO2 origin in southern YGR, which differs from the magma‑carbonate interaction model of central and northern YGR. Ternary mixing calculation based on He-CO2 systematics of hydrothermal gases indicates dominant contributions from carbonate rocks to total carbon inventory, with mantle CO2 contributions absent in southern YGR but discernible in northern YGR. The characteristic high proportions of crustal CO2 (>90%) distinguish the YGR from extensional rifts fed primarily by mantle CO2 in continental rifting zones. Our results reveal a crustal-scale carbon cycle in accretionary wedge of the India-Asia continental collision zone, together with magmatic front setting of the central and northern YGR, outlining a transect of the rift-related CO2 emissions across continental collision zones. This would contribute to better understanding the role of continental assembly in deeply-sourced CO2 emissions and global carbon budget.

Particulate inorganic carbon (PIC) is one of the most important components of carbon cycle in hydropower reservoirs. However, the processes of production, migration, and transformation of PIC in hydropower reservoirs are still unclear. As such, we investigated the concentration and carbon isotope composition of PIC and dissolved inorganic carbon and related environmental parameters of hydropower reservoirs on the Wujiang River, Southwest China, to understand these processes. The observed δ13C datasets demonstrated that the river PIC is derived from exogenous carbonate weathering and endogenous carbonate precipitation, whereas the reservoir PIC is dominated by authigenic PIC driven by phytoplankton. The reservoir PIC concentration and δ13CPIC showed seasonal stratification in the water profile, the extent of which depends on surface photosynthesis and bottom respiration. The influence of phytoplankton on the production and transformation of PIC was different among the reservoirs with different ages and trophic levels, and the δ13C technique can reveal these processes very well. This study improves the comprehensive understanding of carbon cycling in hydropower reservoirs and environmental effects of river damming.

The present study seeks to evaluate the application of the 238U-234U-230Th radioactive disequilibrium methodology for the determination of the regolith production rates in thick weathering profiles marked by long histories, encountered under various climate regimes, but still very little studied by these techniques. For this purpose, 238U-234U-230Th disequilibria have been analyzed in the top 11 m of a lateritic profile developed on a granitic bedrock in south China (Longnan, Jiangxi Province) under a subtropical climate. The results demonstrate that in such a weathering profile the determination of weathering rates from the analysis of U-series nuclides in bulk rock samples cannot be recovered by applying in one step to the entire alteration profile the modeling approach classically used to interpret the U-series nuclides, i.e. the “gain and loss” model. The modeling has to be made on subsections of relatively small size (

The distribution and anomalies of rare earth elements (REEs) of granitic regolith were studied in Inner Mongolia and Hainan Island, China. One profile showed slight REE enrichment of an upper layer and no obvious light REE/heavy REE (LREE/HREE) fractionation (LaN/YbN of 0.9). The second profile was significantly enriched in REEs and enriched in LREEs in the upper portion (LaN/YbN > 1.8). Eu, Ce, and Gd anomalies of the two profiles are different. Slightly negative Eu, Ce, and Gd anomalies in NMG-3-1 indicate slow dissolution of primary minerals and little secondary products; in contrast, a positive Eu anomaly in HN-2 suggests the vegetation cycle may contribute to soil. The Ce anomaly of HN-2 reflects oxidation of Ce and coprecipitation by Fe- and Mn-oxides and organic matter. Correlation between Ce and Gd anomalies in HN-2 suggests Ce and Gd are both influenced by redox-reduction.

Rare earth elements (REEs) can record geologic and geochemical processes. We studied two granitic regolith profiles from different climatic zones in eastern Tibetan Plateau and found that (1) ΣREEs ranged from 119.65 to 275.33 mg/kg in profile ND and 5.11–474.55 mg/kg in profile GTC, with average values of 205.79 and 161 mg/kg, respectively. ΣREEs was higher in accumulation horizon and semi-regolith; (2) Influenced by climate, the fractionation of light and heavy REEs (LREEs and HREEs) varied during weathering. The ratio of LREEs/HREEs in pedosphere was higher than semi-regolith in tropical profile; (3) A negative Eu anomaly in both profiles was the result of bedrock weathering. A positive Ce anomaly was observed in all layers of profile ND, and only in the upper 100 cm of profile GTC. This indicates that redox conditions along the regolith profile varied considerably with climate. (4) Normalized by chondrite, LREEs accumulated much more than HREEs; REE distribution curves were right-leaning with a V-type Eu anomaly in both profiles.

Carbon stable isotope techniques were extensively employed to trace the dynamics of soil organic carbon (SOC) across a land-use change involving a shift to vegetation with different photosynthetic pathways. Based on the isotopic mass balance equation, relative contributions of new versus old SOC, and SOC turnover rate in corn fields were evaluated world-wide. However, most previous research had not analyzed corn debris left in the field, instead using an average corn plant δ 13C value or a measured value to calculate the proportion of corn-derived SOC, either of which could bias results. This paper carried out a detailed analysis of isotopic fractionation in corn plants and deduced the maximum possible bias of SOC dynamics study. The results show approximately 3‰ isotopic fractionation from top to bottom of the corn leaf. The 13C enrichment sequence in corn plant was tassel > stalk or cob > root > leaves. Individual parts accounting for the total dry mass of corn returned distinct values. Consequently, the average δ 13C value of corn does not represent the actual isotopic composition of corn debris. Furthermore, we deduced that the greater the fractionation in corn plant, the greater the possible bias. To alleviate bias of SOC dynamics study, we suggest two measures: analyze isotopic compositions and proportions of each part of the corn and determine which parts of the corn plant are left in the field and incorporated into SOC.

This study investigated the impact of topography and vegetation on distribution of rare earth elements (REEs) in calcareous soils using methods of single extraction and mass balance calculation. The purposes of the study were to set a basis for further research on the biogeochemical REE cycle and to provide references for soil–water conservation and REE-containing fertilizer amendments. The results show a generally flat Post-Archean Average Australian Shale—normalized REE pattern for the studied calcareous soils. REE enrichment varied widely. The proportion of acid-soluble phases of heavy REEs was higher than that of light REEs. From top to bottom of the studied hills, dominant REE sources transitioned from limestone in-situ weathering to input from REE-containing phases (e.g., clay minerals, amorphous iron, REE-containing fluids). Our results indicate that the REE content of calcareous soils is mainly controlled by slope aspect, while the enrichment degree of REEs is related to geomorphological position and vegetation type. Furthermore, the proportion of acid-soluble phases of REEs is mainly controlled by geomorphological position.

Metal contaminations from smelting have been widely reported, however, the study on metal mobility or transfer characteristics in soil profiles after a sudden wastewater overflow is far limited. This study was undertaken to investigate distribution and potential mobility of heavy metals in soils flooded by smelting wastewater in Hechi, China. Total heavy metal/metalloid levels were measured in topsoil, profile and profile pore-water taken in-situ. Enrichment factor (EF) and nemero synthesis index (P N ) were used to detect the contribution of anthropogenic emissions to trace element fluxes and pollution levels, respectively. Soil-water partition coefficient (K d ) was used to reflect the fate and the mobility of elements. Results showed topsoil were seriously contaminated with Sb (289–3100 mg kg − 1 ), Pb (444–6388 mg kg − 1 ), Zn (294–923 mg kg − 1 ), Cu (59–192 mg kg − 1 ), Cd (12–34 mg kg − 1 ), and As (32–405 kg − 1 ), and P N values indicated this area was in severe or strongly pollution level. Higher EF values of Sb, Zn, Cd and As were found in the flooded soils, and P N in flooded area was 5 times of that in the unflooded sites, indicating wastewater flooding aggregated pollution in the low-lying area. The Sb, Pb, and Cd concentrations declined drastically with profile but dropped to constant levels below a depth of about 20 cm. In contrast, Zn and Cu in flooding soils declined first and then increased to another extreme value even at depth of 50 cm. Pore-water profiles exhibited the similar declining trends of vertical metal/metalloid distribution pattern. The K d values ranged from 10 2 –10 6 L kg − 1 , and the mobility and bioavailability of the six elements in the profiles declined in the following order: Sb > Zn > Cu > Cd > As > Pb. The relatively low K d values for some depth intervals may reflect adsorption decrease or migration increase of metal/metalloid. However, it is worth to further study and assess their potential risk to environment in longer period.

The late Carboniferous-early Permian coal seams of the Qinshui Basin in Shanxi Province are the most prolific producer of coalbed methane (CBM) in China. Methane formed in the late Triassic during deep burial and reheating in late Jurassic-early Cretaceous driven by magmatic underplating. Basin inversion brought the coal seams to 400-700 m from the surface in the mid-late Cenozoic. Here we present results of a study aimed at understanding the origin of the methane, and how it was affected by Cenozoic exhumation of the basin. Methane from a 12 km traverse perpendicular to the basin margin in the southeast part of the basin have stable isotope compositions (δ13C = -30.2 to -35.2‰, and δD = -155 to -194‰) indicating a thermogenic origin with limited biogenic input. They are, however, lighter than expected based on coal maturity, and C1/(C2+C3) (>1000) are significantly higher than typical thermogenic methane (

Lithium isotope is potentially useful tracer of continental weathering. However, the factors affecting Li isotope composition in highly weathered saprolites are still largely unclear. In the present study, Li and Nd isotope compositions in saprolites developed on granite from Huizhou, southern China, were analyzed and Li isotope composition in quartz samples separated from the saprolites was determined. The Nd isotope composition of saprolites (eNd = −6.1 ± 0.4, 1σ) was almost identical to that of parent granite (eNd = −5.7), suggesting the eolian deposition in this profile is negligible. The δ7Li value in saprolites varied greatly from −7.7‰ to +14.0‰. Below a depth of 3 m, almost all saprolites were isotopically lighter than the parent granite (+1.0‰). However, above 3 m, δ7Li values were higher in saprolites (+2.2‰ to +14.0‰, average + 7.6‰) than in the parent granite and showed a significant increasing trend toward the surface. Moreover, the δ7Li value showed a negative correlation with the CIA value below 3 m, but a positive correlation above 3 m. Compared with the parent granite, quartz separates had a higher Li concentration (1.1–28.9 mg/kg, average 9.5 mg/kg) and δ7Li value (+12.1‰ to +13.9‰). As weathering progressed, the formation of secondary minerals (such as kaolinite) led to the incorporation of lighter 6Li, which may have contributed significantly to the low δ7Li value in saprolites below 3 m. However, this mechanism could not explain the relative enrichment of heavy 7Li in the upper layer saprolites. The relative enrichment of quartz may contribute significantly to the increase of δ7Li in saprolites. The direct evidence was that Li was abundant and distinctly isotopically heavier in quartz separates. Moreover, quartz content correlated positively with Li concentration (R2 = 0.90, p

Lithium (Li) isotopes have been shown to be fractionated significantly during chemical weathering of silicate rocks. However, previous research has mainly been focused on basalt weathering, whereas the behavior of Li isotopes during the weathering of granite remains unclear. The Li isotopic compositions in the saprolite profile developed on granite was analyzed, as well as several individual primary minerals (K-feldspar, plagioclase, quartz and biotite) in the parent granite. Lithium concentration and the isotopic compositions of the individual primary minerals appear to be heterogeneous. Biotite is rich in Li (369.4 mg/kg), but the Li concentration is very low in other minerals (1.3–11.3 mg/kg). Quartz has the highest δ7Li value (+19.9‰); other minerals contain δ7Li within a fairly narrow range (+5.8‰ to +9.0‰). The saprolite samples were mainly composed of primary minerals and were characterized by low weathering intensity (CIA = 52–60). Lithium was distinctly lost in the saprolites relative to parent granite. Meanwhile, δ7Li values of saprolites were all lower than those of parent granites (−2.0‰ to +3.9‰ vs. +7.1‰, respectively), which systematically decreased with increasing weathering intensity. The mineralogical composition and 87Sr/86Sr ratio in the saprolites suggest that the biotite was preferentially weathered below 120 cm depth in the examined profile, whereas plagioclase weathering mainly occurred above 120 cm depth. The Li released during granite weathering was characteristically different from the isotopes in the primary minerals. Lithium isotopic fractionation during granite weathering is affected by adsorption and/or incorporation of Li by secondary minerals (or clay minerals), and the release of Li from biotite. This study highlights the fact that significant Li isotope fractionation occurs during Li leaching (relatively higher 7Li/6Li ratios) from biotite in the incipient stage of granite weathering, which may help to explain the higher δ7Li values found in the dissolved load from the catchments of low weathering intensity.

Rare earth elements (REEs) and major ions were determined in rainwater samples collected from Guiyang in the acid rain impacted zone of Southwest China. The concentrations of total dissolved and acid-soluble REEs in rainwater are higher than those of most of the world's cities as well as the local surface water. The dissolved REE concentrations are negatively correlated to pH in rainwater. This is consistent with acidification of rainwater resulting in increasing REE concentrations. Speciation calculations using the PHREEQC-Model predict that the free REE metal ion (i.e., Ln3 +), sulfate (LnSO4+), oxalate (LnOx+ and LnOx2−) and fluoride (LnF2 +) complexes were relatively important forms of dissolved REE. Although the contribution to rainwater acidity of oxalic acid is much lower than that of sulfuric acid, the proportion of REE-oxalate complexes is not lower than that of REE-sulfate complexes in rain waters. The rainwater is enriched in the middle REEs (MREE) compared to both the light REEs (LREE) and heavy REEs (HREE). REE-phosphate complexes, phosphatic minerals and a Fe-Mn-oxyhydroxide coating are more likely controls on the development of MREE enrichment in the rainwater. Complexation of sulfate and REE played little role in the development of MREE enrichment, even though sulfate is the most important anion in acidic rainwater. In the shale-normalized REE pattern plot, La showed a clear positive anomaly. La might have two main anthropogenic sources in rainwater. One of the important sources could be automobile emission; another main source of excess La in rainwater could be the REE fertilizer that has been widely used in the agriculture of China for approximately 30 years.

Bulk chemical composition and mineralogy were examined in three soil profiles and a deeper 11-meter profile weathering on a granite ridgeline under subtropical climate conditions in south China. The weathering sequence is delineated by mineralogy and major element variations. Apatite, biotite, hornblende and plagioclase dissolve early during weathering, resulting in nearly 100% Ca and Na loss and significant Mg, Fe and P depletion at depth. The K-feldspar reaction front begins at the depth of depletion of plagioclase, leading to a loss of ~ 80% of the K at the land surface near the bottom of the ridgeline and almost 100% at the top. Dissolution of quartz and other silicates releases about 60% of Si in the profiles. Kaolinite is the dominant clay mineral and it transforms to gibbsite in the uppermost layer. The soil horizon (upper 100 cm) is the zone dominated by pedogenic processes, including active biological activity, physical erosion and influx of high concentrations of atmospheric components (especially CO2 and O2). The pedogenic processes are characterized by low pH (~ 4.54 to 5.85), high clay content (kaolinite: 6–16 wt.%; gibbsite: 2–8 wt.%) and total organic carbon content (0.13–3.93%) and intensive fracturing and dissolution of quartz and K-feldspar compared with the lower horizons. Accumulation of organic material and resistant minerals downslope is attributed to down-ridge movement of water (termed here, interflow) and weathering products in the uppermost 100 cm down the ridgeline. Using a mass balance model calculation for the catena that assumes steady-state soil thickness at all sites, the bottom profile shows the highest apparent total chemical weathering loss rate (~ 14 g m− 2 y− 1) whereas the middle position shows the highest physical erosion loss rate (~ 44 g m− 2 y− 1). SiO2 accounts for about 84% of the chemical weathering outflux from the soil horizons along the ridgeline hillslope. Chemical weathering rates at the bottom of the hillslope may be accelerated by high concentrations of organic material and by dissolution of kaolinite. This study demonstrates that mineral reaction fronts in granite become separated over depth intervals of meters and that elemental fluxes and release mechanisms vary with position along a ridgeline catena.

Intensive soil tillage is a significant factor in soil organic matter decline in cultivated soils. Both cultivation abandonment and foregoing tillage have been encouraged in the past 30 years to reduce greenhouse gas emissions and soil erosion. However, the dynamic processes of soil organic carbon (SOC) in areas of either continuous cultivation or abandonment remain unclear and inconsistent. Our aims were to assess and model the dynamic processes of SOC under continuous tillage and after cultivation abandonment in the black soil of Northeast China. Soil profiles were collected of cultivated or abandoned land with cultivation history of 0–100 years. An isotope mass balance equation was used to calculate the proportion of SOC derived from corn debris (C4) and from natural vegetation (C3) to deduce the dynamic process. Approximately 40% of SOC in the natural surface soil (0–10 cm) was eroded in the first 5 years of cultivation, increasing to about 75% within 40 years, before a slow recovery. C4 above 30 cm soil depth increased by 4.5%–5% or 0.11–0.12 g·kg−1 on average per year under continuous cultivation, while it decreased by approximately 0.34% annually in the surface soil after cultivation abandonment. The increase in the percentage of C4 was fitted to a linear equation with given intercepts in the upper 30 cm of soil in cultivated land. A significant relationship between the change of C4 and time was found only in the surface soil after abandonment of cultivation. These results demonstrate the loss and accumulation of corn-derived SOC in surface black soil of Northeast China under continuous tillage or cultivation abandonment.

This paper investigated the sources and behaviors of sulfate in groundwater of the western North China Plain using sulfur and oxygen isotopic ratios. The groundwaters can be categorized into karst groundwater (KGW), coal mine drainage (CMD) and pore water (subsurface saturated water in interstices of unconsolidated sediment). Pore water in alluvial plain sediments could be further classified into unconfined groundwater (UGW) with depth of less than 30 m and confined groundwater (CGW) with depth of more than 60 m. The isotopic compositions of KGW varied from 9.3‰ to 11.3‰ for δ 34 S SO4 with the median value of 10.3‰ ( n = 4) and 7.9‰ to 15.6‰ for δ 18 O SO4 with the median value of 14.3‰ ( n = 4) respectively, indicating gypsum dissolution in karst aquifers. δ 34 S SO4 and δ 18 O SO4 values of sulfate in CMD ranged from 10.8‰ to 12.4‰ and 4.8‰ to 8.7‰ respectively. On the basis of groundwater flow path and geomorphological setting, the pore water samples were divided as three groups: (1) alluvial–proluvial fan (II 1 ) group with high sulfate concentration (median values of 2.37 mM and 1.95 mM for UGW and CGW, respectively) and positive δ 34 S SO4 and δ 18 O SO4 values (median values of 8.8‰ and 6.9‰ for UGW, 12.0‰ and 8.0‰ for CGW); (2) proluvial slope (II 2 ) group with low sulfate concentration (median values of 1.56 mM and 0.84 mM for UGW and CGW, respectively) and similar δ 34 S SO4 and δ 18 O SO4 values (median values of 9.0‰ and 7.4‰ for UGW, 10.2‰ and 7.7‰ for CGW); and (3) low-lying zone (II 3 ) group with moderate sulfate concentration (median values of 2.13 mM and 1.17 mM for UGW and CGW, respectively) and more positive δ 34 S SO4 and δ 18 O SO4 values (median values of 10.7‰ and 7.7‰ for UGW, 20.1‰ and 8.8‰ for CGW). In the present study, three major sources of sulfate could be differentiated as following: sulfate dissolved from Ordovician to Permian rocks (δ 34 S SO4 = 10–35‰ and δ 18 O SO4 = 7–20‰), soil sulfate (δ 34 S SO4 = 5.9‰ and δ 18 O SO4 = 5.8‰) and sewage water (δ 34 S SO4 = 10.0‰ and δ 18 O SO4 = 7.6‰). Kinetic fractionations of sulfur and oxygen isotopes as a result of bacterial sulfate reduction (BSR) were found to be evident in the confined aquifer in stagnant zone (II 3 ), and enrichment factors of sulfate–sulfur and sulfate–oxygen isotopes calculated by Rayleigh equation were −12.1‰ and −4.7‰ respectively along the flow direction of groundwater at depths of 60–100 m. The results obtained in this study confirm that detailed hydrogeological settings and identification of anthropogenic sources are critical for elucidating evolution of δ 34 S SO4 and δ 18 O SO4 values along with groundwater flow path, and this work also provides a useful framework for understanding sulfur cycling in alluvial plain aquifers.

Excess nutrient (N and P) loads are recognized as the major cause of serious water quality problems in China. River systems play a very important role in nitrate (NO3 −) transportation and transformation in the aquatic environment. To understand and clarify the sources and processes affecting NO3 − in river basins, we have examined spatial and temporal variations of concentration and dual-isotopic composition of NO3 − in the dam-controlled Jialing River, a major tributary of the Yangtze River where land use is dominated by agriculture. Water samples were collected in July 2008 and February 2009 from the main channel of the Jialing River and its major tributaries. The δ15N and δ18O of NO3 − range from 1.5 to 11.0 ‰ (average 6.2 ‰) and −5.0 to 11.1 ‰ (average, 1.6 ‰), respectively. NO3 − isotope data and δ18O of water interpreted in combination with hydrological and chemical data suggest that most of the NO3 − input is from nitrification during the rainy season, and discharge of sewage and manure in the upper course and from cities accounts for much of the NO3 − load during the dry season. The construction of cascade dams has led to retention of Si and a decrease in the Si/N ratio, implying that assimilation and/or denitrification may significantly affect NO3 − in the dam area, as demonstrated by NO3 − and dissolved Si concentrations, and $$\updelta^{ 1 5} {\text{N}}_{{{\text{NO}}_{3} }}$$ and $$\updelta^{ 1 8} {\text{O}}_{{{\text{NO}}_{3} }}$$ values. This study indicates that dual-isotopic data can be used to identify NO3 − pollution sources and the processes NO3 − has undergone during its retention and transport in the watershed of the dam-controlled Jialing River.

The concentrations of rare earth elements in the waters and suspended particles from two alkaline lakes in a carbonate drainage basin of the South China Karst region were determined via ICP-MS. Sequential chemical extraction experiments were conducted on the suspended matter to investigate water-particle interaction processes. Due to their high pH, the alkaline lakes have lower concentrations of dissolved rare earth elements than those reported for most other terrestrial surface waters of the world. Linear regressions between pH and the rare earth element (REE) concentrations over a wide pH range show a “three stage model,” implying the geochemical behavior of dissolved REEs in surface waters is mainly controlled by pH. Shale-normalized patterns of dissolved REEs mainly show a marked enrichment in heavy REEs (HREE), while acid-extracted and organic REEs mainly show convex patterns and the residual fractions have flat patterns. Distinct positive La anomalies were observed in the Lake Aha and its river waters, which also exhibit a very high Mn concentration, indicating severe redox and scavenging conditions. Both negative and positive Ce anomalies were clearly observed in the dissolved phase and extracted fractions of suspended particulate matter. The positive correlation of Ce anomalies with Mn indicates that redox reactions control these Ce anomalies.

Two strains of green microalgae C. reinhardti and C. pyrenoidosa were examined for their biosorption of Mn2+, Fe2+, Co2+, Ni2+, Cu2+, Zn2+, and Cd2+ from aqueous multi-metal solutions. A wide range of biosorption capacities can be observed due to different strains of microalgae and different species of trace metals. This characteristic was ascribed to the distinct components and structures of algal cell walls and the different physicochemical properties of trace metals, such as atomic weight and ion density. C. pyrenoidosa showed higher uptake capacities than C. reinhardti and both of them had a preference for the uptake of cadmium over others in the trace metal solution, suggesting they can be a good biomaterial for biosorption of cadmium. Live microalgal cells displayed a more complex sorption process than dead microalgal cells because of cell assimilation.

The Liao River Basin is one of seven primary river Basins in China. The concentration of dissolved inorganic N (DIN), dual isotopes of NO 3 - using the denitrifier method, the N isotopes of NH 4 + and the N flux in the basin were determined to identify the sources of N and their transformation. The results show that NO 3 - ranges from 0.3 μmol/L to 1316 μmol/L. In general, NO 3 - is the dominant inorganic N species during both flow seasons, but the fraction of NO 3 - /DIN is variable and high NH 4 + is present in some waters. Samples collected from the up-stream portion of the Liao River typically had N isotope values of +8‰ during the high flow season. Most water samples had O isotope values of NO 3 - during the high flow season than the low flow season. The isotopic pattern of NO 3 - suggests that wastewater and soil organic N are the sources of NO 4 + during the high flow season, while wastewater is the main source during low flow season. It appears that no intense denitrification occurs in the river according to the isotopic and chemical data. The N flux of the Liao River system entering the Liao Dong Bay annually is nearly 7.0 × 104 tons, which amounts to 5.0% of the N from chemical fertilizers used in this basin.

For the first time, the river water geochemistry of the Songhuajiang Basin, the third largest river system in China, has been studied in order to understand chemical weathering and associated CO2 consumption rate in a mid- to cool temperate and monsoon-controlled climatic zone. The major ion compositions of the river waters are characterized by the dominance of Ca2+ and HCO 3 - , accounting for 46% and 74% of major cations and anions, respectively. The average total dissolved solids (TDS, 116 mg L−1) and total cation concentration (TZ+, 1388 μEq L−1) of the river waters are similar to those of global major rivers. The chemical weathering rates of carbonate, silicate and evaporites in the whole Songhuajiang Basin are estimated to be approximately 5.15, 2.23 and 0.40 t km−2 a−1, respectively. The total rock weathering rate for the whole Songhuajiang Basin is approximately 7.78 t km−2 a−1, which is at the lower end of the spectrum for global major rivers, and is comparable with that of the Amur and the Congo-Zaire River. The estimated CO2 consumption rates for the whole Songhuajiang Basin are 53.4 × 103 mol km−2 a−1 and 66.6 × 103 mol km−2 a−1 by carbonate and silicate weathering, respectively. As a sub-basin, the 2nd Songhuajiang has the highest (18.9 t km−2 a−1) while the Nenjiang River Basin has the lowest total rock weathering rate (5.03 t km−2 a−1), which indicates important controls of regional climate and lithology. Compared to the large rivers of China, total rock weathering rates increase from north to south, supporting the idea that the climate acts as major control on global chemical weathering. The CO2 consumption rate by silicate weathering within the whole Songhuajiang River Basin, though under mid- to cool temperate climate, is in the same order of magnitude as that of Huanghe (82.4 × 103 mol km−2 a−1) and is not much lower than that of Changjiang (112 × 103 mol km−2 a−1), which suggests that the role of Songhuajiang River weathering in long-term climate change cannot be neglected compared to those of the large rivers of China.

Early Cambrian black shales of South China not only host important sponge, arthropod and other soft-bodied fossils that have helped to trace early metazoan diversification, but also show extreme enrichments of a number of trace metals in particular Ni, Mo and V. In this study, we use a new approach by analyzing rare earth elements in kerogen extracted from the black shales, together with a number of redox-sensitive trace element compositions and total organic carbon (TOC) concentrations in an early Cambrian black shale sequence in Zunyi, Guizhou province, South China, to place better constraints on the oceanic redox conditions and the origin of the extreme metal enrichment. Our data show significant negative Ce anomalies (Ce/Ce* as low as 0.4) occurring in kerogen, which indicate an oxygenated surface environment of primary productivity in consistent with the concept that the organic matter is mainly derived from organisms in the euphotic zone. Mass balance calculation suggests that the kerogen-associated REE can dominate the measured black shale REE budget, while similarity between our measured REE patterns and those of similarly aged phosphorites indicates that the REE content of ancient phosphorites may have also derived initially from organic matter. The redox-sensitive trace elements, such as U, V, Mo, and their ratios of U/Al, V/Al and Mo/Al in black shales show different correlation patterns with TOC contents. The upper black shales show a good metal/TOC correlation, but such a correlation is absent in the lower part. The lower black shales exhibit much higher metal enrichments compared to Black Sea sulphidic (euxinic) sediment. This is taken to indicate the presence of sulphidic bottom waters during the deposition of the lower black shales, including the Ni–Mo ore layer. In contrast, anoxic, non-sulphidic conditions occurred during the deposition of the upper black shales. Taking all these geochemical data together, we suggest that the early Cambrian South China seaway was strongly stratified and stagnant, and that euxinic bottom water conditions may have led to enrichment of the redox-sensitive metals such as U, V and Mo in the lower black shales, and in one case the occurrence of a polymetallic Ni–Mo sulphide ore bed bearing an extraordinarily extreme metal enrichment, which, according to the Mo/TOC and Ni/TOC ratios and much other geochemical evidence, may have been additionally influenced by hydrothermal input of metals within the rift basin as suggested by a number of previous studies.

Vicia villosa is an annual legume plant, and is mainly used for green manure by farmers in southwest China. Field growth experiments were performed on six plots. The concentrations of mineral nutrients and soluble sugar, and the changes of carbon and nitrogen isotopic composition within and among organs of Vicia were determined. Significant differences in legume growth were found in response to soil type and its moisture conditions. The Vicia villosa was relatively well adapted to growth in limestone soils than sandstone soils. The distribution of sugar concentrations and δ13C-differences between roots and leaves indicate that the translocation of sugars from leaves to roots may be restricted by soil drought. Therefore, there was an inhibition of Pi distribution from roots to leaves, resulting in over optimum threshold of N/P ratio. Those may originate from the feedback regulation in the legume, where soluble sugar could not be distributed from leaves to roots. The results of δ15N values in tissues suggest that there should be different preferential use of nitrogen resource by legume during the formation of nodules: before nodule formation the legume preferentially utilizes inorganic nitrogen from soils, but afterwards the nitrogen should be mainly from N2-fixation. Our results indicate that the lack of nodulation development, except for S2, should be ascribed to the factor controlling bi-direction nutrient transfer, which should be efficiency of establishment symbiosis with arbuscular mycorrhiza before nodulation formation. It is predicted that the species of Vicia villosa should be a legume associated with dual symbiosis with rhizobia and mycorrhiza.

We have investigated the diurnal variations of the pCO2 and related environmental factors in the cascade reservoirs with different trophic levels along Wujiang River. In surface water the pCO2 was 357±11 μatm in Hongjiadu Reservoir, 338±48 μatm in Dongfeng Reservoir, 682±303 μatm in Wujiangdu Reservoir, and 1677±429 μatm in Liuguang, respectively. The results indicated that these cascade reservoirs had much lower pCO2 values in surface water than river did, and hypereutrophic reservoir showed larger diurnal variations of pCO2 than meso-eutrophic reservoir. In water column, pCO2 tended to increase with the depth. Phytoplankton and the environmental factors such as temperature and pH had different influences on pCO2 diurnal variations due to different trophic levels, and the effect of phytoplankton on pCO2 variation increased with the increase of trophic level in these reservoirs.

The consumption of CO 2 due to carbonate weathering is thought to be an important terrestrial sink for atmospheric CO 2 . However, the reaction and fate of weathering products may significantly affect the magnitude of the sink. Carbon mass balances were determined in Hongfeng Lake, a small artificial lake located in the carbonate plateau of SW China. This was accomplished by measuring the concentrations of DIC (dissolved inorganic C), DOC (dissolved organic C), POC (particulate organic C), and CO 2 partial pressure in lake waters, inflows and outflows, and in surrounding spring waters. Results show that maximum DIC (mainly HCO 3 - derived from carbonate weathering by CO 2 ) to DOC ratios in the catchment export load reach ∼21, implying that as much as ∼80% of the exported primary production is in the form of HCO 3 - , and, therefore, the CO 2 consumed by carbonate weathering and subsequent DIC export is a critical component of the C balance in this ecosystem. This exported HCO 3 - subsidizes C cycling of aquatic ecosystems in the catchment, and 32% (excluding carbonate-derived C) returns to the atmosphere as CO 2 evasion through the fluvial and lacustrine water–air interface and 10% is stored in lake sediment. This lake has a small CO 2 emission rate (13.2 ± 3.9 mmol m −2 d −1 , or 0.097 mol m −2 a −1 relative to catchment area) compared to mean values for many reservoirs found in temperate and tropical climatic zones. This is likely due in part to low organic C loads supplied by the karst-dominated catchment, and low lake water DOC concentrations. The estimate indicates that more C (39%) returns to the atmosphere and much less (13%) is stored in sediments, implying that the C sink of carbonate weathering may not be as significant as once thought.

The Aha Lake is a seasonal anoxic water system in the southwest of Guiyang City, Guizhou Province, China. Seasonal variations in SO42− concentrations and their isotopic compositions in lake water as well as in the tributaries were investigated in this study. The results showed that sulfate concentrations in river water range from 0.94 to 6.52 mmol/L and their δ34S values range from t14.9‰ and 0.9‰, while lake water has sulfate concentrations ranging from 1.91 to 2.79 mmol/L, and δ34S values from −9.8‰ to −5.9‰. It is suggested that coal mining drainage is the major source of SO42− in the Aha Lake. Rainfall, sewage discharge, sulfide oxidation and gypsum dissolution have made only limited contributions. Different depth-dependent distributions of dissolved SO42− and δ34S were developed for both DB and LJK in summer and winter. Due to water overturn, δ34S values display homogenous vertical distributions in winter and spring. While in summer and autumn, significant positive shifts of δ34S were clearly observed in epilimnion and bottom strata as a result of water stratification. High δ34S values in epilimnion may result from the retention of rainwater during water stratification. Dissimilatory sulfate reduction by bacteria was thought to be responsible for the increase of δ34S value in hypolimnion.

Geochemical studies on REE, trace elements and oxygen isotopes from metamorphic veins and their host metasedimentary rocks in the Zhoutan Group at two localities, Xiangshan and Yihuang, in central Jiangxi Province have been conducted in this paper. The results show that the metamorphic quartz veins inherited the REE and oxygen isotope geochemical characteristics from their host rocks, suggesting that the vein-forming fluids were derived from the host rocks. Additionally, fractionation degrees of the trace element pairs Zr-Hf, Nb-Ta, Y-Ho and U-Th in the veins are different from those of their host rocks. It is also indicated that the veins are the products of the fluids. The metamorphic veins within the Zhoutan Group metasedimentary rocks were formed principally as a result of lateral diffusion of the metamorphic fluids.

Economic reform in China since 1978 has accelerated economic development nationwide hugely, but has also brought about some environmental pollution. In order to identify the primary Pb source to the atmosphere in the central Guizhou region, Pb isotopic ratios in the acid soluble fraction of sediment from Hongfeng Lake were investigated. Lead isotopes in the lake sediments record the history of regional atmospheric Pb pollution. Before the economic reform in 1978, the 208Pb/206Pb and 206Pb/207Pb ratios in the leachates of lake sediments were constant, with a range of 2.0060 to 2.0117 and of 1.2314 to 1.2355, respectively. In the early period of economic reform (1978 to 1988), with the rapid industrial growth in Guizhou province, the acid soluble Pb isotope ratios in the lake sediments changed sharply: the 208Pb/206Pb ratios increased from 2.0212 to about 2.05, while the 206Pb/207Pb ratios decreased from 1.2251 to 1.2060. Emissions from Pb-ore-related industries are suggested to be the major pollution source of Pb in this period. Due to output from a local power plant since 1988, the isotope ratios of the acid soluble Pb in sediments in 1990s are characterized by a little higher radiogenic Pb (208Pb/206Pb = 2.0340–2.0400; 206Pb/207Pb = 1.2122–1.2158) than for the 1980s.

This paper presents hydrogeochemical and S isotopic characteristics of karstic surface and ground water in the karstic aquifers of Zunyi city of Guizhou Province, SW China. The average δ34S value of SO4 is +2.2‰ (n = 28) in ground waters and +7.0‰ (n = 15) in surface waters in the low flow season, while in the high flow season it is +1.0‰ in ground waters and +2.8‰ in surface waters. Natural and anthropogenic sources of the dissolved SO 4 2 - can be discriminated by a combined approach using water chemistry and stable S isotope data. A pollutant source of SO4 is estimated to have very high TDS contents and a narrow range of δ34S values (0‰ to +5.0‰). The water with a distinctively high δ34S value of +30.5‰ originates from an evaporite (gypsum and anhydrite)-bearing aquifer, and the δ34S values lower than −10‰ suggest an origin by oxidation of sulfide minerals in coal seams with intermediate TDS contents.

Land use and land cover changes can cause variations in terrestrial energy, water balance and availability of nutrients. To understand the role of vegetation in regulating the hydrochemistry of karst hillslopes, overland flow and soil seepage water from two hillslopes covered with and without vegetation were studied in the Huanjiang Observation and Research Station for Karst Ecosystems, Guangxi, SW China. Dissolved major ions, as well as isotopic compositions of dissolved inorganic C (DIC) were examined. Water from the vegetated control slope had higher solute concentrations (except NO 3 - ) and lower δ13C values than water from the disturbed slope. The dynamics of K+ and NO 3 - in soil water sampled in time-sequence from the control slope was different from the disturbed slope. Specifically, K+ and NO 3 - concentrations of the control slope decreased gradually over time, while K+ and NO 3 - concentrations of the disturbed slope increased, and other ionic concentrations increased in both of the slopes.

Two reservoirs in series in a Karst area were investigated in this study to understand the impact of river damming on riverine C cycling. Monthly sampling strategy was performed in Hongfeng and Baihua reservoirs, from July, 2007 to June, 2008. DIC and its isotopic compositions were determined. pCO2, and calcite saturation index (SIc) were then calculated. Results show that δ13C-DIC in surface water of these reservoirs responded clearly to the transformation between photosynthesis and respiration, which also changes the inorganic C equilibrium. Based on monthly monitoring data, the major biogeochemical processes along the water column in these reservoirs, was also discussed. It is noted that hypoliminion introduction for hydropower generation and then release can lead to the discontinuity of water chemistry along a river course, and has adverse effects on the downstream environment.

The dual isotopic compositions of dissolved SO 4 2 - in aquatic systems are commonly used to ascertain SO 4 2 - sources and possible biogeochemical processes. In this study, the physical parameters, major anions and isotopic compositions of SO 4 2 - in water samples from Changjiang River (Nanjin) to the East Sea in Changjiang Estuary were determined. The salinity ranged from 0‰ to 32.3‰ in the estuary water samples. The Cl - , SO 4 2 - concentrations and δ18O–H2O values followed the salinity variations from freshwater to seawater, which indicated that mixing processes might be a major factor involved in the distribution of water and solutes. The contents and isotopic compositions of SO 4 2 - suggested that atmospheric deposition, evaporite dissolution and sulphide oxidation were the major sources of dissolved SO 4 2 - in the freshwater of Changjiang River. In addition, the mixing model calculated by contents and isotopic compositions of SO 4 2 - indicated that the mixing of freshwater and sea water was the major factor involved in SO 4 2 - distribution in Changjiang Estuary. However, slightly elevated δ18O–SO4 values were observed in the turbidity maximum zone, which suggested that biological processes might affect the O isotopic compositions of SO 4 2 - there.

Chemical properties and reactivity of fluorescent dissolved organic matter (FDOM) are examined in this paper. They are key issues to understand the biogeochemical processes in the aquatic environments. Typically, FDOM undergoes photochemical transformation and is recalcitrant to microbial degradation, except for the aromatic amino acids that are microbiologically degraded under dark conditions. Experimental results demonstrate that the fluorescence intensity of various FDOM components is depleted upon irradiation (in the hours to 70 days time scale), approximately by 20‐85% for fulvic acid, by 12‐95% for fluorescent whitening agents (FWAs) or commercial detergents, and by 5‐60% for trytophan. Microbial degradation is able to decompose the amino acid tryptophan and similar compounds, by approximately 13‐24% in unfiltered river waters, 67% in unfiltered sewerage samples, and 11% in filtered river samples. The photoreactivity of FDOM is greatly decreased when passing from freshwater (river and lakes) to marine waters, but deep waters in lakes or marine environments are often more sensitive to photodegradation processes than surface waters. The high reactivity of FDOM toward photodegradation could be understood on the basis of its (however complex) chemical structure, considering that many FDOM components can undergo photoionization or otherwise photosensitized oxidation under sunlight. The controlling factors to the photochemical and microbial degradation of FDOM for a variety of waters are extensively discussed. One of the important functions of FDOM is the formation of complexes with transition metals in the aquatic environments, and this review discusses the mechanisms by which FDOM interacts with metals. Further investigations on FDOM, namely the identification of still unknown FDOM components, the metal-FDOM interactions as well as the photochemical and microbial reactivity will give invaluable information on the DOM dynamics in the aquatic environments.

Coal combustion is an important atmospheric pollution source in most Chinese cities, so systematic studies on sulfur and nitrogen in Chinese coals are needed. The sulfur contents in Chinese coals average 0.9 ± 1.0%, indicating that most Chinese coals are low in sulfur. A nearly constant mean δ 34 S value is observed in low sulfur (TS 1 , T 3 and J 3 ). High sulfur Chinese coals (OS > 0.8%), often found at late Carboniferous (C 3 ) and late Permian (P 2 ) in southern China, had two main sulfur sources (original plant sulfur and secondary sulfur). The wide variety of δ 34 S values of Chinese coals (−15‰ to +50‰) is a result of a complex sulfur origin. The δ 15 N values of Chinese coals ranged from −6‰ to +4‰, showing a lack of correlation with coal ages, whereas nitrogen contents are higher in Paleozoic coals than in Mesozoic coals. This may be related to their original precursor plant species: high nitrogen pteridophytes for the Paleozoic coals and low nitrogen gymnosperms for the Mesozoic coals. Different to δ 34 S values, Chinese coals showed higher δ 15 N values in marine environments than in freshwater environments.

Iron isotope compositions of suspended particulate matters (SPM) collected from the Aha Lake, an artificial lake in the karst area of Yun-Gui Plateau, and its tributaries in summer and winter were investigated for our understanding of the behavior of Fe isotopes during iron biogeochemical cycling in lake. δ56Fe values of SPM display statistically negative shift relative to IRMM-014. Samples from the lake display a range from −1.36‰ to −0.10‰ in summer and from −0.30‰ to −0.07‰ in winter, while river samples vary from −0.88‰ to 0.07‰ in summer and from −0.35‰ to −0.03‰ in winter. The average iron isotope composition of aerosol samples is + 0.10‰, which is very similar to that of igneous rocks (0.09‰). The SPM in most rivers and water column showed seasonal variation in δ56Fe value: the δ56Fe values of SPM in summer were lower than in winter. The seasonal variation in δ56Fe value of the riverine SPM should be ascribed to the change in source of particulate Fe and geochemical process in the watershed: More particulate Fe was leached from soil and produced by weathering of pyrite widely distributed in coal-containing strata. It is suggested that both allochthonous inputs and the redox iron cycling control the variations of δ56Fe values for SPM in lake. During summer stratification, an Fe cycle named “ferrous wheel” is established near the redox boundary where the upwardly diffusing Fe(II) is oxidized and the reactive Fe oxides formed will continuously sink back into the reduction zone to complete the cycle. The δ56Fe values for SPM reach the minima, −0.88‰ for DB station and −1.36‰ for LJK station, just near the redox boundary as a result of the Fe cycling, where a rough 45% to 76% of Fe in these particles was produced by the repetitive cycle. Due to random transportation and diffusion, δ56Fe values of the particles near the redox zone distributed into approximately a Gaussian shape. The good negative correlation existed between δ56Fe values and Fe/Al ratios for DB station, suggesting that they together can be used as good indicators of the redox-driven Fe transformations.

Vicia villosa is an annual legume plant. Field-growing experiments were performed on six plots under different soil conditions. Variations in the concentrations of Zn and Cd in tissues were investigated. Differences in distribution patterns between Zn and Cd appeared during growing: the concentrations of Zn in roots in sandstone-derived soils were relatively higher than those in limestone-derived soils, and the uptake patterns of Zn by roots should be similar to those of iron (Fe). However, the concentrations of Cd in roots in limestone-derived soils were higher than those in sandstone-derived soils, and the uptake patterns of Cd by roots should be similar to those of manganese (Mn). On the contrast, the distribution patterns of Zn were similar to those of Mn, while the distribution patterns of Cd were similar to those of Fe in tissues, indicating that the uptake patterns of Zn and Cd were different from distribution patterns.

The sources of dissolved inorganic carbon (DIC) and rock weathering processes were studied in the Houzhai catchment, a typical karstic catchment in the Changjiang River Basin, Southwest China. The carbon isotopic compositions ( δ 13 C DIC ) of DIC in the samples collected from the catchment vary from − 13.5‰ to − 6.9‰, with a mean value of − 9.8‰. The DIC in the catchment is thereby considered to be mainly derived from soil CO 2 and weathering of carbonate rocks. The DIC concentrations and the δ 13 C DIC values show pronounced seasonal variations, with the lowest values being observed during the high flow season (from May to October). The logPCO 2 values in the waters were positively correlated with the DIC contents and negatively correlated to the saturation index of calcite (SIc) and δ 13 C DIC values. These observations indicate that CO 2 derived from organic matter oxidation plays an important role in the dissolution of carbonate for this typical karstic environment. Based on a chemical mass balance, the weathering rate of carbonate rocks in the Houzhai catchment was estimated to be approximately 133 t/km 2 /year or 584 × 10 3 mol/km 2 /year in terms of CO 2 consumption rate, which is higher than the reported values for other rivers in Southwest China.

The Xijiang River, the mainstream of the Zhujiang (Pearl) River, which is the second largest river in China in terms of discharge, flows through a large carbonate rock region in South China. The chemical and Sr isotopic compositions of the Xijiang waters were determined during the high-flow season in order to understand the chemical weathering processes, associated CO2 consumption and anthropogenic influences within the carbonate-dominated basin. The major ion compositions of the river waters are characterized by the dominance of Ca2+, Mg2+, HCO 3 - and are significantly rich in SO 4 2 - . The SO 4 2 - is mainly derived from the oxidation of sulfide minerals and acid precipitation caused by coal combustion. Chemical and Sr isotopic compositions of the river waters indicate that four reservoirs (carbonates, silicates, evaporites and anthropogenic inputs) contribute to the total dissolved loads. The chemical weathering rates of carbonates and silicates for the Xijiang basin are estimated to be approximately 78.5 and 7.45 ton km−2 a−1, respectively. The total chemical weathering rate of rocks for the Xijiang basin is approximately 86.1 ton km−2 a−1 or 42 mm ka−1, which is much higher than global mean values. The budgets of CO2 consumption by carbonate and silicate weathering are estimated to be 284 × 109 and 54.3 × 109 mol a−1, respectively. It would appear that H2SO4 is involved as a proton donor in weathering reactions in the Xijiang basin; calculated results show that the contribution of cations from rock weathering induced by H2SO4 accounts for approximately 11.2%. Results from this study show that the flux of CO2 released into the atmosphere is approximately 0.1 × 106 mol C km−2 a−1 or 0.41 × 1012 g C a−1 produced by H2SO4-induced carbonate weathering in the basin. When extrapolated to the entire surface area of carbonate in SW China, the flux of CO2 released to the atmosphere by H2SO4-induced carbonate weathering is about 1.41 × 1012 g C a−1.