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The sources, transport, and transformation of terrestrial dissolved organic matter (DOM) in large river systems are of great interest due to their importance in the regional and global carbon cycles. However, knowledge of these factors is limited, especially for different DOM compositions coupling with hydrodynamics at the basin scale. To investigate the dynamics of different DOM compositions in a large river system, we characterized the dissolved organic carbon (DOC), chromophoric DOM (CDOM), and dissolved lignin at both moderate (September–October 2009) and high (August 2012) discharges in the Changjiang River basin. We found that extensive soil erosion resulted in the increased DOC concentration in the middle to lower reaches in 2012. In 2009, the transformation of DOM was dominated by flocculation and photo degradation due to the low flow velocity and depressed particle suspension. In 2012, the degradation of CDOM and dissolved lignin was coupled and dominated by microbial degradation and photo degradation. In 2012, CDOM (absorbance and fluorescence) and dissolved lignin concentrations were positively correlated, demonstrating the potential of using CDOM to quantitatively estimate dissolved lignin. Mass balance estimations of the DOM fluxes further confirmed that 17.0% (6.1%) of DOC, 24.2% (32.3%) of dissolved lignin, and 14.5% (0.8%) of CDOM were degraded at high (moderate) discharge. This study reveals contrasting transformation processes of DOM compositions with different sources and reactivities along the Changjiang River under different hydrological conditions, and it provides new insights into the linkage between the chemical and optical properties of DOM in large river systems. Key Points: Main controls on DOM removal were flocculation and photo degradation (microbial degradation and photo degradation) at moderate (high) dischargeCDOM can be used to trace dissolved lignin at high discharge, whereas at moderate discharge, CDOM and dissolved lignin were decoupledAt high (moderate) discharge, 17.0% (6.1%) of DOC, 24.2% (32.3%) of dissolved lignin, and 14.5% (0.8%) of CDOM were degraded [ABSTRACT FROM AUTHOR]

The regional carbon cycle on continental shelves has created great interest recently due to the enigma of whether these areas are a carbon sink or a source. It is vital for a precise carbon cycle model to take the bioavailability of dissolved organic carbon (DOC) into account, as it impacts the sink and source capacity, especially on dynamic shelves such as the East China Sea. Nine bio-decomposition experiments were carried out to assess differences in the bioavailability of DOC. Samples were collected from different water masses in the East China Sea, such as the Coastal Current, the Taiwan Current, and the Kuroshio Current, as well as from the Changjiang (Yangtze River), the main contributor of terrestrial DOC in the East China Sea. This study aimed to quantify and qualify bioavailable DOC (BDOC) in the East China Sea. Both the degradation constant of BDOC and the carbon output from microorganisms have been quantitatively evaluated. Qualitatively, excitation-emission matrix fluorescence spectra (EEMs) were used to evaluate the intrinsic reasons for BDOC variation. By using EEMs in conjunction with parallel factor analysis (PARAFAC), five individual fluorescent components were identified in this study: three humic-like and two protein-like components (P1, P2). The highest P1 and P2 fluorescence intensities were recorded in the coastal water during a phytoplankton algal bloom, while the lowest intensities were recorded in the Changjiang estuary. Quantitatively, BDOC observed during the incubation ranged from 0 to 26.1 µM. The DOC degradation rate constant varied from 0 to 0.027 (d −1 ), and was lowest in the Changjiang and highest in algal bloom water and warm shelf water (the Taiwan current). The Taiwan Current and mixed shelf water were the major contributors of BDOC flux to the open ocean, and the East China Sea was a net source of BDOC to the ocean. The results verified the importance of BDOC in regional carbon cycle modeling. Combining the data of BDOC and EEMs, there is significant positive linear correlation between BDOC and protein-like peaks ( P <0.01). The transformation and degradation of BDOC, which plays an important role in the microbial carbon pump, could be viewed by EEMs. This suggests the potential of EEMs in the quantitative prediction of BDOC in large-scale carbon cycle modeling. [ABSTRACT FROM AUTHOR]

Ciprofloxacin, a third-generation fluoroquinolones (FQs) antibiotic, is observed to increasingly pollute the environment. In this study, a three-dimensional reduced graphene oxide-attapulgite-based catalyst Fe2O3/RGO-ATP was prepared and used to analyze the degradation of ciprofloxacin in a heterogeneous Fenton reaction. The heterogeneous catalyst Fe2O3/RGO-ATP was prepared by a one-step hydrothermal method, and the samples were characterized using BET(Brunauer-Emmett-Teller) surface area, Raman spectroscopy, X-ray diffraction (XRD), Fourier infrared (FTIR) spectroscopy, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The effect of reaction time, temperature, pH, initial concentration, H2O2 dosage and reuse time on the degradation of ciprofloxacin by the catalyst Fe2O3/RGO-ATP was investigated. The optimum conditions of degradation of ciprofloxacin are observed to be 60 °C, pH 5, H2O2 concentration of 2.9724 mmol/L, and initial ciprofloxacin concentration of 50 mg/L. The catalyst could be reused several times with a decline in catalytic capacity. Fourier-transform ion cyclotron resonance mass spectrometer (FT) was also employed to study the degradation products of ciprofloxacin in the aqueous solution. The results show that the heterogeneous catalyst Fe2O3/RGO-ATP possessed an excellent ability for the catalytic degradation of ciprofloxacin. Direct hydroxyl oxidation is noted to be the main pathway of degradation of ciprofloxacin, and no defluorination reaction is observed during the degradation process. [ABSTRACT FROM AUTHOR]

To control the water pollution in the Pearl River Estuary (PRE), a series of measures have been enacted in recent years. The efficacy of these measures on water quality improvement is, however, currently unknown. To evaluate the variation of water quality in response to the pollution control measures in the PRE during the last decade (2008–2017), our study conducted a long-term monitoring program of estuarine water in the representative city Guangzhou that targeted fecal coliform (F. Coli), biochemical oxygen demand (BOD5), chemical oxygen demand (CODCr), potassium permanganate index (CODMn), petroleum, total nitrogen (TN), ammonia nitrogen (NH3–N) and total phosphorus (TP). In the last decade, F. Coli, BOD5, CODCr and CODMn, petroleum and NH3–N have shown a significant reduction by 78.8%, 50.9%, 37.5%, 18.9%, 75.0% and 25.0%, respectively. In contrast, TN and TP remained stable. Water quality index calculations indicated that the water quality was elevated from the marginal–fair level to the good level, particularly after 2012. The biochemical pollutants and nutrients in the estuarine water most likely originated from the upper river due to the wastewater discharge, fecal pollution and agricultural input. The success of pollutant reduction could thus be attributed to industrial upgrading and relocation, as well as the improvement of the sewage treatment system in Guangzhou. However, efficient approaches to reduce TN pollution should be implemented in the future. [ABSTRACT FROM AUTHOR]

Arsenic (As) contamination in groundwater is a global environmental geochemical problem that threatens over 100 million people around the world. Although groundwater As enrichment has been demonstrated to result from some major complex processes, including competitive desorption by anions and reductive release of As from iron (Fe) oxyhydroxides due to microbial respiration of dissolved organic matter (DOM), knowledge of the detailed interactions among these processes and their respective contributions is still limited. In this study, we aimed to elucidate the key variables that regulate the evolution of dissolved As in shallow groundwater from a typical As-contaminated region of the Pearl River Delta (PRD) after comprehensive statistical analysis of hydrogeochemical characteristics. The results showed that the highest concentration of As in the groundwater samples (n = 77) was 57 μg/L, with 9% of samples exceeding the drinking water standard. In comparison with other regions with geogenic As contamination in groundwater, the relatively low As concentration range is primarily controlled by the well-oxygenated environment, which also contributed to the dominance of As(V) (19.5–100.0%, median of 100.0%). Hierarchical cluster analysis (HCA) and principal component analysis (PCA) suggested that the presence of As in groundwater may be impacted by the reduction process of Fe/Mn oxyhydroxides and by competitive anions. Further analysis using structural equation modeling (SEM) indicated that the increased concentration of As(V) in the shallow groundwater was primarily induced by the competitive roles of phosphate and silicate, explaining 65.2% and 31.5% of total As(V), respectively. In contrast, the presence of As(III) was strongly explained by DOM (23.8%, 12.4%, and 5.7% from microbial humic-like, terrestrial humic-like, and protein-like components, respectively) and Fe (31.8%), followed by competitive desorption (26.3%), revealing the dominant contribution from DOM-facilitated Fe reduction to As(III) enrichment. Our study empirically demonstrated that decreasing the concentrations of phosphate and reactive organic matter can effectively alleviate As contamination in groundwater. [Display omitted] • Phosphate, Fe reduction, and organic matter trigger As release in PRD groundwater. • As species in As(V)-dominated groundwater are controlled by the oxidizing environment. • Phosphate and silicate contributed substantially to the competitive desorption of As(V). • Release of As(III) is probably facilitated by iron (oxyhydr)oxide reduction. • Increased As(III) was related to increasing microbial humic-like components. [ABSTRACT FROM AUTHOR]