Identification of nitrate sources in tap water sources across South Korea using multiple stable isotopes: Implications for land use and water management.

Stable nitrate isotopes (δ15N-NO3 and δ18O-NO3) in conjunction with stable water isotopes (δ18O-H2O and δD-H2O) were used to identify nitrogen (N) sources and N-biogeochemical transformation in tap water sources sampled from 11 water purification plants across South Korea. The raw water sources are taken from rivers within the water supply basins, which indicates the quality of tap water is highly dependent on surrounding the land use type. We estimated the proportional contribution of the various N sources (AD: atmospheric deposition; SN: soil nitrogen; CF: chemical fertilizer; M&S: manure/sewage) using Bayesian Mixing Model. As a result, the contribution of N sources exhibited large seasonal and spatial differences, which were related to the type of land use in the water supply basins. Commonly, the M&S and SN were the dominant N source during the dry and wet seasons in almost regions, respectively. However, in the regions with high N loading ratios from urban and industrial sources, the M&S was the dominant N source during both the wet and dry seasons. In addition, the regions were characterized by high NO3- concentrations due to the decreased dilution effect of precipitation during the dry seasons. In contrast, the SN was the dominant N source in the regions with high N loading ratios from agricultural areas during both the wet and dry seasons. The NO3--N concentration during the wet season was significantly higher than those during the dry season in these regions due to the input of non-point sources with high concentrations. Meanwhile, denitrification and nitrification were observed in the watersheds. It is important to understand the isotope fractionation due to N-biogeochemical transformation for considering the potential misinterpretations of the origin and fate NO3-. Collectively, our findings provide a basis on N source control strategies to ensure tap water quality in complex land use areas.

Exploring applicability of end member mixing approach for predicting environmental reactivity of dissolved organic matter.

Despite the wide applications of end member mixing analysis (EMMA) for assigning the sources of dissolved organic matter (DOM) in aquatic environment, there was no study attempting to test the applicability of EMMA for predicting environmental reactivity of DOM. This study aimed to explore the feasibility of EMMA, or the concept of ideal mixing behavior of end members, for describing several well-known DOM reactivities using two DOM end member sources (i.e., soil and algae) at varying mixing ratios. The selected DOM reactivities were trihalomethane formation potential (THMFP), mineral adsorption amount, pyrene binding, membrane resistance, and biodegradation potential. Among the tested DOM functions, all were found to follow the ideal mixing behavior, presenting the linear relationships between the source mixing ratios and the tested reactivity with the R2 value of >0.80. The ideal mixing behavior of the DOM functions was more pronounced than that based on several spectroscopic indicators derived from UV absorption and fluorescence spectroscopy. This study provided insight into potential applicability and limitation of EMMA approach in monitoring and predicting environmental functions of DOM in aquatic systems where identified DOM sources are mixed and vary dynamically with the mixing ratios.

Enhancing copper binding property of compost-derived humic substances by biochar amendment: Further insight from two-dimensional correlation spectroscopy.

Little is known about the environmental impacts of biochar (BC) amendment on the immobilization of heavy metals in compost-treated fields. In consequence, this study was designed to explore the effects of BC amendment on the copper (Cu) binding properties of compost-derived humic substances (HS). To this end, unamended and 4.7% (by wet weight) BC-amended compost were incubated in parallel with regular wetting for 6 months. The stability constants for Cu binding, calculated based on the fluorescence quenching technique, were higher for the compost-derived HS with versus without BC amendment. The result suggests that BC addition to compost may intensify the immobilization of heavy metals in a compost-treated field. Copper binding efficacy increased after the incubation with or without BC amendment. However, the enhanced Cu binding efficacy of the BC-amended HS was preserved even after the long-term incubation. Two-dimensional correlation spectroscopy revealed that the short wavelength fulvic-like fluorescence followed by humic-like fluorescence were preferentially associated with Cu binding. However, the range of wavelengths that tracked the binding of Cu were modified after BC amendment. This study evidenced beneficial and synergetic effects of BC amendment on the abatement of the potential environmental risk from heavy metal polluted field on a long-term basis.

'Evidence of an auxin signal pathway, microRNA167-ARF8-GH3, and its response to exogenous auxin in cultured rice cells'.

MicroRNA167 (miR167) was shown to cleave auxin responsive factor 8 (ARF8) mRNA in cultured rice cells. MiR167 level was found to be controlled by the presence of auxin in the growth medium. When cells grew in auxin-free medium, miR167 level decreased, resulting in an increase in the level of ARF8 mRNA. Cells growing in the normal growth medium containing auxin showed a reversed trend. It was also shown that expression of OsGH3-2, an rice IAA-conjugating enzyme, was positively regulated by ARF8. Delivery of synthesized miR167 into cells led to decrease of both ARF8 mRNA and OsGH3-2 mRNA. This study provides an evidence in which the exogeneous auxin signal is transduced to OsGH3-2 through miR167 and ARF8 in sequence. This proposed auxin signal transduction pathway, auxin-miR167-ARF8-OsGH3-2, could be, in conjunction with the other microRNA-mediated auxin signals, an important one for responding to exogeneous auxin and for determining the cellular free auxin level which guides appropriate auxin responses.