| The sediment in Dianchi lake, a hypereutrophic plateau lake in southwest China, was investigated and sampled, and the concentration of heavy metals (Cu, Cr, Ni, Zn, Pb, Fe, Mn and Cd) in the sediment was determined. Their spatial distribution and sources were analyzed using multivariate statistics. The result indicated that studied metals exhibited three distinct spatial patterns, that is, Cu, Pb, Zn and Ni had a similar distribution; Cd and Cr presented a similar distribution; Fe and Mn presented a quite different distribution than other metals, which indicates their different sources and geochemistry processes. Correlation and cluster analysis (CA) provided origin information on these metals and the CA result for metals was corresponding to the three spatial patterns. Principal component analysis (PCA) further displayed their source characteristics and impact factors, that is, Cu, Pb, Zn, Ni, Cd and Cr were mainly derived from anthropogenic sources, and Fe and Mn were mainly the result of natural processes. Sediment assessment was conducted using geoaccumulation index (Igeo), potential ecological risk indices (RI) and USEPA guidelines. The result indicated that, generally, Cd was the most serious risk metal; Pb and Cu posed moderate potential ecological risk; Cr, Zn and Ni had slight ecological risk; Fe and Mn were not polluted. Comparison of the assessment tools showed that each of the methods had its limitation and could bias the result, and the combined use of the methodologies and local knowledge in the practice would give a more comprehensive understanding of the metal risk or pollution. Statistical analysis also indicated that nutrients had different impacts on Fe, Mn and trace elements, which implies that in the assessment of metal risk, nutrients impact should be taken into consideration especially for eutrophic waters, although the impact mechanism of nutrients is yet to be further studied.Particle size composition of the surface sediments (0-10cm) were analyzed at three representative sites (Caohai, mid-lake, southern Waihai) from Dianchi Lake. Physiochemical properties and the concentrations of Cu, Cr, Ni, Zn, Pb, Fe, Mn and Cd in different particle-size fractions of the sediment were measured. The distributions in the surface sediment of different particle size were studied, as well as the normalization of metals concentrations was taken. The results showed that the surface sediments of the Dianchi Lake mainly distributed in<250μm particle size. Silty (4-63μm) made up of the biggest fraction in the four sizes, averaged out at60%。 Besides, the clay (<4um) was secondary, accounting for19%. The average ratio of heavy metals in silts (<63μm) reached79%, which was significantly higher than in extremely fine sands (63-125μm) and fine sands (125-250μm). Cr, Cd, Cu, Pb, Zn and Ni have a peak concentration in the range of4-63μm, having similar concentration and absorption properties. Fe and Mn have no strong enrichment in these four particle sizes, which may be due to their different source and geochemical processes. Results of heavy metals in different size fractions normalized by the clay concentration in agreement with the results of reference element normalization, and the heavy metals concentrations take on consistent variation. Effect of the sediment particle size on metals should be taken into account when developing standard methods related to the studies of sediments trace metal contamination, when comparing the results obtained for various areas in various laboratories, and when studying source contamination identification.In this study, the equilibrium membrane (500/2000/3500/5000u) dialysis method was employed to determine the molecular weight distribution of dissolved organic matter in the Dianchi Lake sediment. Ion selective electrode (ISE) and fluorescence technology were performed to analyze spectral characteristics of different molecular weight DOM reacted with Cu and Pb, as well as explore the effect of molecular weight on the interaction between heavy metal and DOM. As shown in the results, the ratio of the Caohai DOM with molecular weight higher than3500u was61%in the total TOC, and the DOM with molecular weight in3500-5000u was primary. The ratio of the Waihai DOM with molecular weight lower than3500u was74% in the total TOC, and the DOM with molecular weight in500-2000u was primary. Taken as a whole, Caohai DOM with higher molecular weight than Waihai. The UV absorption ratio values (E3/E4) which was used to characterize the humification degree, aromatic structure, and molecular weight of DOM covered a diverse range of molecular weight were in the range1.57to6.00, and the degree of humification and aromaticity of DOM increased with increasing the molecular weight. The ISE results and3DEEM spectral characteristics showed that Cu was mainly present in the fraction from molecular weight2000to3500u DOM; Pb tended to associate with low molecular weight (<500u) DOM. Complexing capacity (C) and distribution coefficients (Kd) were used to estimate the capability of Cu and Pb associated with DOM between the truly dissolved and the associated phases. It turned out that, the maximum value of Cu was in the rang of2000-3500u, in Caohai and Waihai were717.65mg/g and340.27mg/g, respectively; the maximum value for Pb was in lower than500u, in Caohai and Waihai were2988.84mg/g and5073.45mg/g, respectively. |
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