Search

Nitrate source identification in river systems is important for water quality management. Recently, the oxygen isotopic anomaly of nitrate in atmospheric deposition (Δ17O atm) is used to identify unprocessed atmospheric nitrate in river systems to reduce the uncertainty caused by the wide range of δ18O. In high-elevation regions, such as the Qinghai-Tibetan Plateau (QTP) featured with lower temperature and pressure as well as strong radiation, the Δ17O atm might be different from that in low-elevation regions, but no relevant studies have been reported. In this work, Δ17O atm in the QTP was studied, and the fingerprints of nitrate isotopes in synthetic fertilizer, livestock manure, domestic sewage, and soil organic nitrogen (SON) were identified and used to quantify various source contributions to riverine nitrate in the Yellow River and Changjiang River source regions located in the QTP during 2016–2017. The results showed that the average of Δ17O atm in the QTP was 16.4‰, lower than the range (19–30‰) reported for the low-elevation regions. The possible mechanism is decreased O 3 as well as increased hydroxyl and peroxy radical levels in the troposphere caused by the climate condition and ozone valley in the QTP will affect the production pathways of atmospheric nitrate. By combining the sewage discharge data with the output results of the SIAR (stable isotope analysis in R) model based on the stable isotope data, manure was determined to be one of the major sources to riverine nitrate for both rivers. The contributions of various sources to riverine nitrate were 47 ± 10% for manure, 30 ± 5% for SON, 10 ± 4% for atmospheric precipitation, 9 ± 2% for synthetic fertilizer, and 4 ± 0% for sewage in the Yellow River source region. This study indicates that the unique atmospheric conditions in the QTP have led to a lower Δ17O atm value, and atmospheric source makes a considerable contribution to riverine nitrate in the QTP. Unlabelled Image • The average of Δ17O atm value of atmospheric nitrate in the QTP was 16.4‰. • The Δ17O atm value in the QTP was lower than the low-elevation regions. • The SIAR model was used to trace the contribution of riverine nitrate sources. • Manure was one of the major sources to riverine nitrate in the QTP. • Atmospheric precipitation accounted for 10%–19% of riverine nitrate in the QTP. [ABSTRACT FROM AUTHOR]

Abstract Rivers are important sites of both nitrogen removal and emission of nitrous oxide (N 2 O), a powerful greenhouse gas. Previous measurements have focused on nitrogen-rich temperate rivers, with cold, low-nitrogen river systems at high-altitude receiving less attention. Here, nitrogen removal rates were estimated by directly measuring dissolved N 2 and N 2 O of the Yellow River in its source region of the Tibetan Plateau, a frigid high-altitude environment. We measured the dissolved N 2 and N 2 O using N 2 :Ar ratio method and headspace equilibrium technique, respectively. Dissolved N 2 in the river water ranged from 337 to 513 μmol N 2 L−1, and dissolved N 2 O ranged from 10.4 to 15.4 nmol N 2 O L−1. Excess dissolved N 2 (△N 2) ranged from −8.6 to 10.5 μmol N 2 L−1, while excess dissolved N 2 O (△N 2 O) ranged from 2.1 to 8.3 nmol N 2 O L−1; they were relatively low compared with most other rivers in the world. However, N 2 removal fraction (△N 2 /DIN, average 21.6%) and EF 5r values (N 2 O − N/NO 3 − N, range 1.6 × 10−4–5.0 × 10−2) were comparable with many other rivers despite the high altitude for the Yellow River source region. Furthermore, the EF 5r values increased with altitude. Estimated fluxes of N 2 and N 2 O to the atmosphere from the river surface ranged from −67.5 to 93.5 mmol N m−2 d−1 and from 4.8 to 93.8 μmol N m−2 d−1, respectively, and the nitrogen removal from rivers was estimated to be 1.87 × 107 kg N yr−1 for the Yellow River source region. This is the first report of nitrogen removal for a frigid high-altitude river; the results suggest that N removal and N 2 O emission from cold high-altitude rivers should be considered in the global nitrogen budget. Graphical abstract Unlabelled Image Highlights • Excess dissolved N 2 and N 2 O in the Yellow River source region were lower than other rivers. • N 2 O emission factor increased with the elevation of the Yellow River in its source region. • N 2 removal fraction and N 2 O emission factor in this study were comparable with other rivers. • The nitrogen removal from the Yellow River source region was about 1.87 × 107 kg N yr−1. [ABSTRACT FROM AUTHOR]

The emission characteristics of motorcycles using gasoline and E10 (90% gasoline and 10% ethanol by volume) were investigated in this article. Exhaust and evaporative emissions of three motorcycles were investigated on the chassis dynamometer over the Urban Driving Cycle (UDC) and in the Sealed Housing for Evaporative Determination (SHED) including regulated and unregulated emissions. The regulated emissions were detected by an exhaust gas analyzer directly. The unregulated emissions including carbonyls and volatile organic compounds (VOCs) were sampled through battery-operated air pumps using tubes coated with 2,4-dinitrophenylhydrazine (DNPH) and Tenax TA, respectively. The experimental results showed that the emission factors of total hydrocarbons (THC) and carbon monoxide (CO) from E10 fueling motorcycles decreased by 26%–45% and 63%–73%, while the emission factor of NOx increased by 36%–54% compared with those from gasoline fueling motorcycles. For unregulated emissions, the emission amount of VOCs from motorcycles fueled with E10 decreased by 18%–31% while total carbonyls were 2.6–4.5 times higher than those for gasoline. For evaporative emissions of THC and VOCs, for gasoline or E10, the diurnal breathing loss (DBL) was higher than hot soak loss (HSL). Using E10 as a fuel does not make much difference in the amount of evaporative THC, while resulted in a slightly growth of 14%–17% for evaporative BETX (benzene, toluene, ethylbenzene, xylene). [ABSTRACT FROM AUTHOR]

Riverine nitrogen loss makes a large contribution to the global nitrogen budget. However, little research has focused on nitrogen loss from large turbid rivers with high suspended sediment (SPS) concentrations. In this work, nitrogen loss amounts and related drivers were studied across fluvial networks of the Yellow River, the largest turbid river in the world, based on in situ measurement of nitrogen gas (N 2) and nitrous oxide (N 2 O) fluxes at the water-air interface via the diffusion model and floating chamber methods, respectively. The results showed that N 2 and N 2 O fluxes from the Yellow River ranged from −2.93 to 48.54 mmol m−2 d−1 and from 2.42 to 712.23 μmol m−2 d−1, respectively, with the nitrogen loss amount estimated to be 5.56 × 107 kg N yr−1 for the Yellow River, including the mainstem and main tributaries. Other than nitrogen compounds and water temperature, nitrogen loss from the Yellow River was also affected by SPS. Both N 2 flux: DIN and N 2 O flux: DIN ratios increased remarkably in the middle reaches, probably due to a sharp increase of SPS concentration in this section. Furthermore, greater SPS concentrations were a main cause for the higher N 2 O flux in the middle reaches than those in the other reaches of the Yellow River, and the possible effect of SPS was stronger on N 2 O flux than on N 2 flux. This study demonstrates the importance of SPS in nitrogen loss from large turbid rivers, and more research is demanded to further clarify the role of SPS in riverine nitrogen cycle. Unlabelled Image • Nitrogen loss from a turbid river network was studied based on N 2 and N 2 O fluxes. • Nitrogen loss from the Yellow River was affected by suspended sediment (SPS). • The effect of SPS concentration on N 2 O flux was stronger than that on N 2 flux. • High SPS concentration was a main cause for the high N 2 O flux from the middle reaches. [ABSTRACT FROM AUTHOR]