Risk Assessment of Nitrogen and Phosphorus Loss in a Hilly-Plain Watershed Based on the Different Hydrological Period: A Case Study in Tiaoxi Watershed

Non-point source pollution is widely considered a serious threat to drinking water. Eutrophication in Chinese watershed is mainly due to nitrogen and phosphorus output from agricultural source. Taihu Lake is a typical eutrophic lake in China, a basin representative for the study of the temporal-spatial characteristics of pollution loading of nitrogen and phosphorus to provide scientific basis for reasonable estimation and targeted control measures of nitrogen and phosphorus loss. Based on data from nitrogen and phosphorus loss in agricultural land, livestock breeding, domestic discharge and aquaculture, this study calculated the levels of nitrogen and phosphorus comprehensive loss risk for each pollution source. Using the superposition of ArcGIS raster data, we also described the spatial distribution of nitrogen and phosphorus comprehensive loss risk by the formula of comprehensive loss risk. The results showed that critical risk areas of nitrogen and phosphorus loss mainly originated from livestock breeding and agricultural land during flood period in Tiaoxi watershed. Agricultural land and livestock breeding sources formed major parts of nitrogen loss, accounting for 30.85% and 36.18%, respectively, while phosphorus loss mainly originated from livestock breeding (56.28%). During non-flood period, integrated management of livestock breeding and domestic discharge requires much attention to control nitrogen and phosphorus loss in the critical risk area. Finally, it is of great practical significance to propose spatial-temporal targeted measurements to control nitrogen and phosphorus pollution in watershed for various periods and different areas

Seasonal variation in the mineralogy of the suspended particulate matter of the lower Changjiang river at Nanjing, China

The source and temporal changes of minerals transported by the world's large rivers are important. In particular, clay minerals are important in evaluating the maturity of suspended sediments, weathering intensity, and source area. To examine seasonal changes in mineralogical compositions of the Changjiang River (CR), suspended particulate matter (SPM) samples were collected monthly for two hydrological cycles in Nanjing city and then were studied using X-ray diffraction (XRD), diffuse reflectance spectrophotometry (DRS), X-ray fluorescence spectrometry (XRF), and chemical analyses. The resultsindicate that the concentration of CR SPM rangesfrom 11.3 to 152 mg/L and ishighly correlated to the rate of water discharge, with a greater concentration in flood season and lower concentrations during the dry season. CaO, MgO, and NaO increase with increasing discharge whereas AlO decreases sharply with increasing discharge. Dolomite, calcite, and plagioclase show strikingly similar seasonal variations and increase with increasing discharge with maximum concentrations in the flood season. In contrast, the clay mineral content exhibits the opposite trend with the lowest concentrationsin the flood season. Illite dominatest he clay mineralsof the CR SPM, followed by chlorite, kaolinite, and smectite. Illite and kaolinite show distinctly seasonal variations; SPM contains more illite and less kaolinite during the flood season than during the dry season. The illite chemistry index and crystallinity, as well as kaolinite/illite ratio, all indicate intense physical erosion in the CR basin during the rainy season. Total iron (Fe) and highly reactive iron (Fe) concentrations display slight seasonal changes with the smallest values observed during the flood season. Goethite is the dominant Fe oxide mineral phase in the CR SPM and hematite is a minor component, as revealed by DRS analyses. The FeT flux and FeHR flux are 2.78×10 T/y and 1.19×10 T/y, respectively

Distribution and Phytoavailability of Potentially Toxic Metals in Different Fe/Mg Mine Tailings

The environmental risk of potentially toxic metals in tailing soils is of universal concern. We conducted a 3-month pot experiment to research the distribution and variations of potentially toxic metals (PTMs), and the translocation and accumulation capability of these metals (Cr, Ni, Mn, Cu, Zu) in natural plants for three Fe/Mg tailing soils (serpentine-type, olivine-type and magnetite-type) with growth of a grass plant-Imperata cylindrica. We used comparative analysis, regression analysis and correlation analysis to process relevant experimental data. Results showed the rhizosphere tailing soils decreased from 3.70% to 16.8%, compared to the bulk soils, after growth of Imperata cylindrica, and the acid soluble fraction of Mn, Cu and Zn increased significantly. Cu and Zn were more bioavailable than other PTMs, especially for serpentine-type tailing soils. Linear regression analysis indicated that non-residual fractions showed different effects on metal concentrations of Imperata cylindrica. The non-residual metal fractions of serpentine-type and olivine-type tailing soils showed better correlations with metal concentrations in grass plants than those of magnetite-type tailing soils. We found that the chemical compositions of tailing soils showed remarkable effects on Ni and Mn compared with other elements, especially Mg and Al. Overall, the grass plant can alter the metal distribution, enhance metal bioavailability and promote land use of Fe/Mg tailing soils