[Tracking Riverine Nitrate Sources and Transformations in the Yiluo River Basin by Nitrogen and Oxygen Isotopes].

The impacts of natural processes and anthropogenic input on riverine nitrate (NO-3) could be identified by NO-3 concentrations and nitrogen and oxygen isotope ratios (δ15N-NO-3 and δ18O-NO-3); however, the effects of variable land use on riverine NO-3 sources and transformations remain unclear. In particular, the human impacts on riverine NO-3 in mountain areas are still unknown. The Yihe River and Luohe River were used to elucidate this question due to their spatially heterogeneous land use. Hydrochemical compositions, water isotope ratios (δD-H2O and δ18O-H2O), and δ15N-NO-3 and δ18O-NO-3 values were utilized to constrain the NO-3 sources and transformations affected by different land use types. The results indicated that ① the mean nitrate concentrations in the Yihe River and Luohe River waters were 6.57 and 9.29 mg·L-1, the mean values of δ15N-NO-3 were 9.6‰ and 10.4‰, and the average δ18O-NO-3 values were -2.2‰ and -2.7‰, respectively. Based on the analysis of δ15N-NO-3 and δ18O-NO-3 values, the NO-3 in the Yihe and Luohe Rivers were derived from multiple sources, and nitrogen removal existed in the Luohe River, but the biological removal in the Yihe River was weak. ② The contributions of different nitrate sources were calculated using a Bayesian isotope mixing model (BIMM) based on δ15N-NO-3 and δ18O-NO-3 values of river water in the mainstream and tributaries with spatial locations. The results revealed that sewage and manure had major impacts on riverine nitrate in the upper reaches of both the Luohe River and Yihe River, where forest vegetation was widely distributed. However, the contributions from soil organic nitrogen and chemical fertilizer were higher in the upper reaches than in downstream ones. The contributions of sewage and manure still increased in the downstream reaches. Our results confirmed the primary impacts of point sources, e.g., sewage and manure, on riverine nitrate in the studied area, and the contributions of nonpoint sources, e.g., chemical fertilizer, had not increased as the agricultural activities elevated the downstream. Therefore, more attention should be paid to point source pollution treatment, and the high-quality development of ecological civilization in the Yellow River Basin should be maintained.

[Factors Affecting Nitrate Concentrations and Nitrogen and Oxygen Isotope Values of Effluents from Waste Water Treatment Plant].

Urban domestic sewage is one of the important nitrate (NO-3) sources for surface water; however, their NO-3 concentrations and nitrogen and oxygen isotope values (δ15N-NO-3 and δ18O-NO-3) remain unclear, and the factors affecting NO-3 concentrations and δ15N-NO-3 and δ18O-NO-3 values of effluents in the waste water treatment plant (WWTP) are still unknown. Water samples in the Jiaozuo WWTP were collected to illustrate this question. Influents, clarified water in the secondary sedimentation tank (SST), and effluents of the WWTP were sampled every 8 h. The ammonia (NH+4) concentrations, NO-3 concentrations, and δ15N-NO-3 and δ18O-NO-3 values were analyzed to elucidate the nitrogen transfers through different treatment sections and illustrate the factors affecting the effluent NO-3 concentrations and isotope ratios. The results indicated that ① the mean NH+4 concentration was (22.86±2.16) mg·L-1 in the influent and decreased to (3.78±1.98) mg·L-1 in the SST and continuously reduced to (2.70±1.98) mg·L-1 in the effluent of the WWTP. The median NO-3 concentration was 0.62 mg·L-1 in the influent, and the average NO-3 concentration increased to (33.48±3.10) mg·L-1 in the SST and gradually increased to (37.20±4.34) mg·L-1 in the effluent of the WWTP. ② The mean values of δ15N-NO-3 and δ18O-NO-3 were (17.1±10.7)‰ and (19.2±2.2)‰ in the influent of the WWTP, the median values of δ15N-NO-3 and δ18O-NO-3 were 11.9‰ and 6.4‰ in the SST, and the average values were (12.6±1.9)‰ and (5.7±0.8)‰ in the effluent of the WWTP. ③ The NH+4 concentrations of influent had significant differences compared to those in the SST and the effluent (P<0.05). The reduction of NH+4 concentrations in the SST was due to the above nitrification during the aerobic treatment process, which transferred NH+4 to NO-3. The NH+4 concentrations in the SST had no significant differences with that in the effluent of the WWTP (P>0.05). ④ The NO-3 concentrations in the influent had significant differences with those in the SST and the effluent (P<0.05), and minor NO-3 concentrations but relatively high δ15N-NO-3 and δ18O-NO-3 values in the influent were probably due to denitrification during the pipe sewage transportation. The obviously increased NO-3 concentrations (P<0.05) but decreased δ18O-NO-3 values (P<0.05) in the SST and the effluent resulted from water oxygen incorporation during the nitrification. The above results confirmed the impacts of aerobic and anaerobic treatment processes on NO-3 concentrations and isotope ratios of effluent from the WWTP and provided scientific basis for the identification of sewage contributions to surface water nitrate via average δ15N-NO-3 and δ18O-NO-3 values.

[Dissolved Ion Concentrations and Isotope Values in Agricultural Fertilizer Locally Applied in Henan Province].

Agricultural fertilizers (AFs) have provided vegetation with necessary nutrients, but unabsorbed constituents have been retarded in soil, potentially affecting the quality of adjacent surface water and groundwater. AFs element contents and stable isotope compositions have often been utilized to assess and calculate AFs pollution to nitrate and sulfate in surface water and groundwater; however, due to various AFs applied, the dissolved ion concentrations and isotope ratios are still unknown. This study collected commercial AF widely utilized in Henan province, China, to constrain their ion concentrations and isotope values. The dissolved ions (1 g AFs dissolved in 1 L ultrapure water), sulfate sulfur, and oxygen isotope values(δ34S and δ18O) were analyzed, and total nitrogen (TN) contents coupled with nitrogen isotope values(δ15N) in solid AFs were determined to elucidate their elemental and isotopic compositions. These characteristics provided a scientific basis for further assessing their contributions to surface water and groundwater contaminations. The results indicated that pH values in the AFs solutions varied from 3.6 to 10.2, with a mean value of 6.7±1.5 (n=30, 1σ). Sulfate (SO42-) and nitrate (NO3-) concentrations ranged from 4.38 mg·L-1 to 827.29 mg·L-1 and from 1.34 mg·L-1 to 208.90 mg·L-1, with median values of 192.80 mg·L-1 and 13.51 mg·L-1 and average values of (256.19±239.83) mg·L-1 (n=30) and (37.07±53.21) mg·L-1 (n=29), respectively. Dissolved sulfate δ34S and δ18O values in AFs varied from -3.5‰ to 19.0‰ and from 6.7‰ to 18.5‰, with median values of 4.1‰ and 10.1‰ and mean values of (5.8±5.5)‰ (n=22, 1σ) and (10.7±2.7)‰ (n=22, 1σ), respectively. TN and δ15N values in AFs ranged from 0.5% to 38.9% and from -2.7‰ to 3.4‰, with median values of 13.3% and 0.0‰ and average values of (14.8±9.3)% (n=25) and 0.0±1.5‰ (n=24, 1σ), respectively. The lower averaged δ34S values and positive averaged δ18O values potentially resulted from sulfuric acids added as raw materials, giving rise to a negative relationship between pH values and SO42- concentrations (P<0.05). The δ15N values of AFs were close to that of air N2, corresponding to the fact that NO3--N and NH4+-N were synthesized via air N2. Our results revealed the dissolved ion concentrations of SO42-, NO3-, and NH4+ and their δ34S, δ18O, and δ15N values of typically applied AFs in Henan province, which provided the scientific basis for studying the AFs contributions to SO42- and NO3- pollutions in surface water and groundwater surroundings.

Combining metal and sulfate isotopes measurements to identify different anthropogenic impacts on dissolved heavy metals levels in river water.

Dissolved heavy metals (DHMs) contamination has raised global concern for ecological and human health development. Weathering of sulfide-bearing ore metals can produce acidic, sulfate-rich solutions in the presence of water and oxygen (O2), and DHMs are released to deprave the river water quality. Sulfur and oxygen isotope signatures (δ34SSO4 and δ18OSO4) could identify this pyrite-derived sulfate; however, it is yet not well known whether the δ34SSO4 and δ18OSO4 values could limit the DHMs sources and illustrate anthropogenic impacts on DHMs along the river corridor. We tried to solve this problem through field works in the Luohe River and Yihe River, two tributaries of the Yellow River, China, where metal sulfide mine activities mostly occurred upstream, but agricultural and domestic behaviors concentrated in the lower plain reaches. In the Luohe River upper areas, δ34SSO4 values had negative correlations with concentrations of cadmium (Cd) (p < 0.01), nickel (Ni) (p < 0.05), molybdenum (Mo) (p < 0.01), uranium (U) (p < 0.01), and SO42- (p < 0.01). However, as the δ34SSO4 values increased downstream in the Luohe River, concentrations of copper (Cu) (p < 0.05), mercury (Hg) (p < 0.05), Ni (p < 0.05), and SO42- (p < 0.01) simultaneously elevated. The Bayesian Isotope Mixing Model (BIMM) results via δ34SSO4 values demonstrated 64.3%-65.3% of SO42- from acid mine drainage (AMD) in the Luohe River's upper reaches and 63.5%-67.7% in the Yihe River's upper reaches, and about 33% from sewage and industrial effluents in the Luohe River's lower reaches and 27% in Yihe River's lower reaches. Our results confirmed the different anthropogenic impacts on the DHMs concentrations in Luohe River and Yihe River and provided a robust method for DHMs sources appointment and pollution management in river systems.

Isotope evidence for temporal and spatial variations of anthropogenic sulfate input in the Yihe River during the last decade.

Pyrite oxidation and sedimentary sulfate dissolution are the primary components of riverine sulfate (SO42-) and are predominant in global SO42- flux into the ocean. However, the proportions of anthropogenic SO42- inputs have been unclear, and their tempo-spatial variations due to human activities have been unknown. Thus, field work was conducted in a spatially heterogeneous human-affected area of the Yihe River Basin (YRB) during a wet year (2010) and drought years (2017/2018). Dual sulfate isotopes (δ34S-SO42- and δ18O-SO42-) and Bayesian isotope mixing models were used to calculate the variable anthropogenic SO42- inputs and elucidate their temporal impacts on riverine SO42- flux. The results of the mixing models indicated acid mine drainage (AMD) contributions increased from 56.1% to 83.1% of upstream sulfate and slightly decreased from 46.3% to 44.0% of midstream sulfate in 2010 and 2017/2018, respectively, in the Yihe River Basin. The higher upstream contribution was due to extensive metal-sulfide-bearing mine drainage. Sewage-derived SO42- and fertilizer-derived SO42- inputs in the lower reaches had dramatically altered SO42- concentrations and δ34S-SO42- and δ18O-SO42- values. Due to climate change, the water flow discharge decreased by about 70% between 2010 and 2017/2018, but the riverine sulfate flux was reduced by only about 58%. The non-proportional increases in anthropogenic sulfate inputs led to decreases in the flow-weighted average values of δ34S-SO42- and δ18O-SO42- from 10.3‰ to 9.9‰ and from 6.1‰ to 4.4‰, respectively. These outcomes confirm that anthropogenic SO42- inputs from acid mine drainage (AMD) have increased, but sewage effluents SO42- inputs have decreased.

[Spatial and Temporal Variation of Mercury in Municipal Sewage Sludge in China].

In order to determine the occurrence of mercury (Hg) in the dewatered sewage sludge (SS) from municipal wastewater treatment plants (MWTPs) in China, 315 SS samples were collected from 40 MWTPs. The total Hg (THg) contents of the sludge samples were analyzed using a DMA-80 Hg analyzer. It was found that THg in the samples ranged from 0.45-15.42 mg ·kg-1. The THg data followed a log-normal distribution with a geometric mean of (2.19±3.16) mg ·kg-1. THg contents in all the sludge samples meet the criteria set for disposal (by co-landfilling) of MWTPs sludge (GB/T 23485-2009). In terms of THg contents, 97.8% of the sludge was suitable for land application in neutral and alkaline soils, while 86.7% of the sludge was suitable for land application in acidic soil. THg in SS varied greatly, not only among cities (variation coefficient of 105%), but also in the same MWTP (variation coefficient of 0.6%-53.6% over seven days). Mercury contents in SS of China showed a descending trend of North > Northeast > Northwest > Southwest > East > Central > South China. Using the corresponding urban soil background values of THg as references, Hg pollution levels of SS were evaluated using the geological cumulative index method. It was found that SS from more than 60% of the cities sampled were heavily polluted by Hg. Mercury contents in the SS of China showed a temporal trend of increasing then decreasing, with 2000-2009 being the peak period. Results of the present study provide significant data support for the prevention and control of mercury pollution in sewage and SS in China.

[Distribution of Different Mercury Species in the Waterbody at Sanmenxia Reservoir].

In order to obtain the distribution of different species of mercury (Hg) in the water in the Sanmenxia Reservoir, cold vapor atomic fluorescence spectrometry (CVAFS) and aqueous phase ethylation derivatization-gas chromatography-atomic fluorescence spectrometry (GC-CVAFS) methods were used for the analysis of total Hg (THg) and methylmercury (MeHg) in water and sediment samples, respectively. It was found that the levels of THg, dissolved mercury, and particulate mercury in the water ranged from 1.65-9.65, 0.80-3.16, and 0.70-7.81 ng·L-1, respectively. The THg in the water could meet the requirement for the Class I criterion in the national surface water environmental quality standard (GB 3838-2002). The amounts of MeHg, dissolved MeHg, and particulate MeHg in the water samples were 0.05-0.36, 0.02-0.14, and ND-0.26 ng·L-1, respectively. No evident seasonal or spatial patterns for Hg were observed. The THg and MeHg in the Sanmenxia Reservoir were within the ranges for those in uncontaminated waterbodies worldwide. The amount of THg in the sediments was (92.96±10.65) ng·g-1 and (80.06±19.14) ng·g-1, while the amount of MeHg in the corresponding sediment samples was (0.33±0.14) ng·g-1 and (0.50±0.19) ng·g-1 for wet and dry seasons, respectively. The ratios of MeHg/THg in the sediment of the Sanmenxia Reservoir were relatively small in comparison to those in other aqueous systems, indicating that methylation might play a minor role in the biogeochemistry of Hg in the Sanmenxia Reservoir. This might be attributed to the high dissolved oxygen levels of the bottom water and low organic carbon content of the sediments.

[Speciation and spatial-temporal variation of mercury in the Xiaolangdi Reservoir].

In order to investigate the occurrence status of mercury in Xiaolangdi Reservoir, water, surface sediments, pore water and fish samples were collected and analyzed for the contents of total mercury (THg) and methylmercury (MeHg). Cold vapor atomic fluorescence spectrometry and aqueous phase ethylation derivatization-gas chromatography-atomic fluorescence spectrometry methods were used for the analysis of THg and MeHg, respectively. Bioaccumulation of THg in fish of Xiaolangdi Reservoir was then discussed. It was found that THg contents in water were 0.71-1.42 ng x L(-1) and 0.90-2.49 ng x L(-1) during dry and wet seasons, respectively, while the MeHg content in water was below the method detection limit. The THg content in water during both seasons could meet the requirement of Class I criterion of national surface water environmental quality standard (GB 3838-2002). The THg contents in sediments were 95.66-172.52 ng x g(-1) and 51.74-90.42 ng x g(-1), while the MeHg contents in the corresponding sediment samples were 0.18-0.39 ng x g(-1) and 0.09-0.26 ng x g(-1) for dry and wet seasons, respectively. The ratios of MeHg/THg in sediment were relatively small in comparison to those in other aqueous systems. This might be attributed to the high dissolved oxygen content of bottom water and low organic carbon content of the sediments. The THg concentrations in pore water of sediments were 5.46-41.04 ng x L(-1) and 4.27-9.49 ng x L(-1), and the MeHg concentrations were 0.07-1.01 ng x L(-1) and 0.09-0.99 ng x L(-1), respectively. The THg concentration was significantly higher than that of the overlying water, indicating the diffusion of Hg from the sediment to the water. The THg concentration in fish muscle tissues varied from 43.47 to 304.98 ng x g(-1), while the MeHg concentration varied from 10.77 to 265.23 ng x g(-1). The MeHg content in fish muscle tissues could meet the requirement of national food safety standards( GB 2762-2012) (Non carnivorous fish 500 ng x g(-1), Carnivorous fish 1 000 ng x g(-1)). The bioaccumulation factors of THg were 1.3 x 10(5) for bighead carp, 9.3 x 10(4) for barracuda, 4.7 x 10(4) for crucian carp, 5.0 x 10(4) for sharpbelly, 1.7 x 10(5) for yellow catfish, and 3.9 x 10(4) for arch fish, respectively.