Dual-isotope-based source apportionment of nitrate in 30 rivers draining into the Bohai Sea, north China.

Excessive nitrate (NO3-) in rivers can lead to water quality deterioration, and can also be directly input into estuaries and oceans, thus posing a serious threat to the stability of their ecosystems. In this study, the concentration, isotopes and sources of NO3- in 30 rivers discharging into the Bohai Sea were comprehensively investigated. The mean concentration of NO3--N was 2.24 ± 2.11 mg L-1, with obvious seasonal and spatial variations. In total, 104.24 kt of NO3--N was discharged into the Bohai Sea annually, to which the Yellow River Basin and Liao River Basin made the largest contributions. The range of δ15N-NO3- was -1.1‰ to +33.2‰ (mean value, +11.4 ± 5.0‰), with no significant seasonal or spatial differences; the mean value of δ18O-NO3- was +9.4 ± 7.2‰, with much higher values seen in June. Based on the MixSIAR model, manure (24.3 ± 7.5%) and sewage (19.1 ± 14.5%) were the primary sources of NO3- in the 30 rivers, followed by NO3- fertilizers (16.3 ± 12.5%), soil N (15.5 ± 11.9%), atmospheric deposition of NO3- (13.5 ± 5.7%) and NH4+ fertilizers (11.4 ± 8.9%). This finding highlights the vital roles of sewage and manure management in riverine NO3-. Using a mathematical method, the contributions of various sources to each river were simulated. The results indicated that management of the Yellow River, Daliao River, Liao River, and Xiaoqing River is more urgently needed than that of other rivers to control Bohai NO3- pollution. We believe that this finding will provide guidance for scientific management of NO3- pollution in these 30 rivers and the Bohai Sea.

Methylobacter accounts for strong aerobic methane oxidation in the Yellow River Delta with characteristics of a methane sink during the dry season.

Recent investigations demonstrate that some coastal wetlands are atmospheric methane sinks, but the regulatory mechanisms are not clear. Here, the main pathway and operator of methane oxidation in the Yellow River Delta (YRD) wetland, a methane source in the wet season but a methane sink in the dry season, were investigated. The anaerobic oxidation of methane (AOM) and aerobic methane oxidation (AMO) abilities of wetland soil were measured, and the microbial community structure was analyzed. The experimental results showed that AMO was active throughout the year. In contrast, AOM was weak and even undetected. The microbial community analysis indicated that Methylomicrobium and Methylobacter potentially scavenged methane in oxic environments. A representative strain of Methylobacter, which was isolated from the soil, presented a strong AMO ability at high concentrations of methane and air. Overall, this study showed that active AMO performing by Methylobacter may account for methane sink in the YRD wetland during the dry season. Our research not only has determined the way in which methane sinks are formed but also identified the potential functional microbes. In particular, we confirmed the function of potential methanotroph by pure culture. Our research provides biological evidence for why some wetlands have methane sink characteristics, which may help to understand the global methane change mechanism.

Heterogeneous activation of peroxymonosulfate by a biochar-supported Co3O4 composite for efficient degradation of chloramphenicols.

Herein, a new peroxymonosulfate (PMS) activation system was established using a biochar (BC)-supported Co3O4 composite (Co3O4-BC) as a catalyst to enhance chloramphenicols degradation. The effects of the amount of Co3O4 load on the BC, Co3O4-BC amount, PMS dose and solution pH on the degradation of chloramphenicol (CAP) were investigated. The results showed that the BC support could well disperse Co3O4 particles. The degradation of CAP (30 mg/L) was enhanced in the Co3O4-BC/PMS system with the apparent degradation rate constant increased to 5.1, 19.4 and 7.2 times of that in the Co3O4/PMS, BC/PMS and PMS-alone control systems, respectively. Nearly complete removal of CAP was achieved in the Co3O4-BC/PMS system under the optimum conditions of 10 wt% Co3O4 loading on BC, 0.2 g/L Co3O4-BC, 10 mM PMS and pH 7 within 10 min. The Co3O4/BC composites had a synergistic effect on the catalytic activity possibly because the conducting BC promoted electron transfer between the Co species and HSO5- and thus accelerated the Co3+/Co2+redox cycle. Additionally, over 85.0 ± 1.5% of CAP was still removed in the 10th run. Although both SO4- and OH were identified as the main active species, SO4- played a dominant role in CAP degradation. In addition, two other chloramphenicols, i.e., florfenicol (FF) and thiamphenicol (TAP), were also effectively degraded with percentages of 86.4 ± 1.3% and 71.8 ± 1.0%, respectively. This study provides a promising catalyst Co3O4-BC to activate PMS for efficient and persistent antibiotics degradation.

Trophic strategy of diverse methanogens across a river-to-sea gradient.

Methanogens are an important biogenic source of methane, especially in estuarine waters across a river-to-sea gradient. However, the diversity and trophic strategy of methanogens in this gradient are not clear. In this study, the diversity and trophic strategy of methanogens in sediments across the Yellow River (YR) to the Bohai Sea (BS) gradient were investigated by high-throughput sequencing based on the 16S rRNA gene. The results showed that the diversity of methanogens in sediments varied from multitrophic communities in YR samples to specific methylotrophic communities in BS samples. The methanogenic community in YR samples was dominated by Methanosarcina, while that of BS samples was dominated by methylotrophic Methanococcoides. The distinct methanogens suggested that the methanogenic community of BS sediments did not originate from YR sediment input. High-throughput sequencing of the mcrA gene revealed that active Methanococcoides dominated in the BS enrichment cultures with trimethylamine as the substrate, and methylotrophic Methanolobus dominated in the YR enrichment cultures, as detected to a limited amount in in situ sediment samples. Methanosarcina were also detected in this gradient sample. Furthermore, the same species of Methanosarcina mazei, which was widely distributed, was isolated from the area across a river-to-sea gradient by the culture-dependent method. In summary, our results showed that a distribution of diverse methanogens across a river-to-sea gradient may shed light on adaption strategies and survival mechanisms in methanogens.

Exopolysaccharide production by an indigenous isolate Pseudomonas stutzeri XP1 and its application potential in enhanced oil recovery.

In this study, a rapid and efficient method for screening biopolymer producers was established using 96-well plates. An indigenous biopolymer producer Pseudomonas stutzeri XP1 was isolated from Xinjiang oil reservoirs, China. Strain XP1 can grow and produce 16 g/l biopolymer using corn starch and nitrate. Produced biopolymer increased culture viscosity up to 2384 mPa s. Biopolymer showed rheological properties and pseudo-plastic behavior. The viscosity of 8 g/l biopolymer solution kept higher than 25 mPa s at 20-50 °C and pH values (5-9) and increased to 7600 mPa s with NaCl concentrations increasing to 2%. Gel permeation chromatography data showed that the biopolymer average molecular mass was 1.65 × 106 Da. Gas chromatography revealed that the monosaccharide composition in biopolymer was glucose. Core flooding experiments revealed that extra 13.56% of oil was recovered by in situ biopolymer production of strain XP1. Properties of strain XP1 and the biopolymer produced make them promising for enhanced oil recovery.