[en] Highlights: • Nitrate was the dominant species of DIN in Liao River. • High fraction of NH₄⁺/DIN observed during low flow season. • Nitrate in rivers originated mainly from nitrification and sewage based on isotopic pattern. • About 7.0 × 10⁴ ton N/yr entered the Bay annually amounting to 5% of N fertilizer. - Abstract: The Liao River Basin is one of seven primary river Basins in China. The concentration of dissolved inorganic N (DIN), dual isotopes of NO₃^- using the denitrifier method, the N isotopes of NH₄⁺ and the N flux in the basin were determined to identify the sources of N and their transformation. The results show that NO₃^- ranges from 0.3 μmol/L to 1316 μmol/L. In general, NO₃^- is the dominant inorganic N species during both flow seasons, but the fraction of NO₃^-/DIN is variable and high NH₄⁺ is present in some waters. Samples collected from the up-stream portion of the Liao River typically had N isotope values of <+8‰, while those from the middle and lower portions had values of >+8‰ during the high flow season. Most water samples had O isotope values of <+10‰ during the high flow season. During the low flow season, the ranges of N and O isotopic values were limited, with average values of +10.3‰ and +4.9‰, respectively. There is a wider isotopic range of NO₃^- during the high flow season than the low flow season. The isotopic pattern of NO₃^- suggests that wastewater and soil organic N are the sources of NO₄⁺ 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

[en] Highlights: • Dual sulfate isotopes were used to elucidate natural and anthropogenic sources in alluvial aquifers. • Infiltration, mixing and bacterial reduction were main processes controlling sulfate behaviors in groundwater. • Enrichment factors and ratio of sulfur and oxygen isotope of sulfate had been calculated. • Local sulfur cycles model had been establish for further management of groundwater. - Abstract: 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 δ³⁴S_SO4 with the median value of 10.3‰ (n = 4) and 7.9‰ to 15.6‰ for δ¹⁸O_SO4 with the median value of 14.3‰ (n = 4) respectively, indicating gypsum dissolution in karst aquifers. δ³⁴S_SO4 and δ¹⁸O_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 (II₁) group with high sulfate concentration (median values of 2.37 mM and 1.95 mM for UGW and CGW, respectively) and positive δ³⁴S_SO4 and δ¹⁸O_SO4 values (median values of 8.8‰ and 6.9‰ for UGW, 12.0‰ and 8.0‰ for CGW); (2) proluvial slope (II₂) group with low sulfate concentration (median values of 1.56 mM and 0.84 mM for UGW and CGW, respectively) and similar δ³⁴S_SO4 and δ¹⁸O_SO4 values (median values of 9.0‰ and 7.4‰ for UGW, 10.2‰ and 7.7‰ for CGW); and (3) low-lying zone (II₃) group with moderate sulfate concentration (median values of 2.13 mM and 1.17 mM for UGW and CGW, respectively) and more positive δ³⁴S_SO4 and δ¹⁸O_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 (δ³⁴S_SO4 = 10–35‰ and δ¹⁸O_SO4 = 7–20‰), soil sulfate (δ³⁴S_SO4 = 5.9‰ and δ¹⁸O_SO4 = 5.8‰) and sewage water (δ³⁴S_SO4 = 10.0‰ and δ¹⁸O_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 (II₃), 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 δ³⁴S_SO4 and δ¹⁸O_SO4 values along with groundwater flow path, and this work also provides a useful framework for understanding sulfur cycling in alluvial plain aquifers

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

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

[en] Highlights: • Enrichment of ⁷Li in highly weathered saprolites developed on granite was observed. • Lithium was relatively abundant and isotopically heavy in quartz. • Quartz enrichment was the major cause of high δ⁷Li in saprolites. 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 (ε_Nd = −6.1 ± 0.4, 1σ) was almost identical to that of parent granite (ε_Nd = −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 < 0.01) and δ⁷Li value (R² = 0.90, p < 0.01) in the upper layer saprolites. The results showed that a 10% increase in Li due to quartz enrichment (δ⁷Li = ~+13‰) resulted in a +1.3‰ increase in δ⁷Li in the saprolites. Our results highlight that relative enrichment of quartz may result in isotopically heavier Li in highly weathered saprolites developed on granite, which may help to explain the higher δ⁷Li values detected near the surface layer of weathering profiles.

[en] Highlights: • High levels of dissolved As are observed in YTR system. • Hot springs are main source of dissolved As in the upper reaches of YTR. • Natural attenuation of dissolved As in main channel is mainly due to dilution. • Lowest dissolved As is observed in July and August due to dilution process. • Weathering of As-containing minerals inputs much of As in rivers in wet-season. High levels of dissolved arsenic (As) have been reported in many rivers running though the Tibetan Plateau (TP), the “Water Tower of Asia”. However, the source, spatiotemporal variations, and geochemical behavior of dissolved As in these rivers remain poorly understood. In this study, hot spring, river water, and suspended particulate material samples collected from the Yarlung Tsangpo River (YTR) (upper reaches of the Brahmaputra River) system in 2017 and 2018 were analyzed. Spatial results shown that the upper reaches of YTR (Zone I) have comparatively high levels of dissolved As ([As]_dissolved: mean 31.7 μg/L; 4.7–81.6 μg/L; n = 16), while the tributaries of the lower reaches (Zone II) have relatively low levels (mean 0.54 μg/L; 0.11–1.3 μg/L; n = 7). Seasonal results shown that the high [As]_dissolved (6.1–22.4 μg/L) were found in September to June and low [As]_dissolved (1.4–3.7 μg/L) were observed in July to August. Geothermal water is suspected as the main source of the elevated As levels in YTR due to the extremely high [As]_dissolved in hot springs (1.13–9.76 mg/L) and abundance of geothermal systems throughout TP. However, the seasonal results suggested that weathering of As-containing rocks and minerals is also a key factor affecting the [As]_dissolved in the river water in July to August (wet-season). Natural attenuation of As in main channel is dominated by dilution process due to the lower As concentrations in tributaries, but mostly occurred by both dilution and adsorption (or co-precipitation) processes in tributaries. This work highlights that the weathering process may have an important contribution to the dissolved As in the river waters in wet-season, and the geochemical behavior of As is largely transported conservatively in the main channel and relative non-conservatively in the tributaries in YTR system.