The bioavailability of five divalent cationic heavy metals （Pb, Cd, Cu, Zn and Ni） in 10 superficial sediment samples from Baihua Lake was assessed based on the molar ratio of simultaneously extracted metals （SEMs） to acid volatile sulfide （AVS）. Atomic absorption spectrometry （AAS） and X-ray powder diffraction （XRD） were used to determine the heavy metal concentrations and examine the mineralogy of the crystalline phases, respectively. The AVS loadings in sediments from Baihua Lake ranged from 64.30 to 350.08 ~rnol/g （dry weight）. The corresponding SEM levels for the sampling sites varied from 1.770 to 14.660 vrnol/g. The molar ratio of SEMs to AVS ranged from 0.014 to 0.084 with a mean value of 0.034. The XRD analysis also confirmed the presence of some metal sulfides in sediments from Baihua Lake. The SEMs/AVS ratios for all sampling sites were significantly lower than 1.0, indicating that AVS in the sediments was sufficient to bind the five heavy metals; thus, these heavy metals are currently not significantly bioavailable to benthic organisms. Comparing the SEMs results to published guideline values for metal toxicity to benthic organisms in sediments, however, suggests that Zn and Ni pose a risk at some sampling locations in Baihua Lake.
This study was conducted to evaluate the distribution characteristics of phosphorus and its species in 14 sediments samples collected from Lake Hongfeng based on sequential extraction. Lake Hongfeng, a major drinking-water source for Guiyang City in southwestern China, is one of the largest artificial reservoirs located in a typical karstic area of the Yunnan-Guizhou Plateau. The results of this study indicate that the average percentages of DP, Al-P, Fe-P, Ca-P and OP in the lake sediments were 0.52, 6.59, 6.09, 42.85 and 40.27, respectively. The concentrations of organic phosphorus (OP) were lower than those of inorganic phosphorus (IP), which consisted mainly of calcium-bound phosphorus (Ca-P). The high concentrations of Ca-P may temporarily control the release of phosphorus from the sediments because it is a relatively stable, inert, and non-bioavailable phosphorus fraction. However, a large number of phosphate solubilizing bacteria can transform insoluble phosphate into bioavailable forms. Moreover, the concentrations of total phosphorus (TP) in the lake sediments were high; thus, the potential for the release of phosphorus from the sediments to the water column and phosphorus bioavailability were still significant. Further statistical analyses of the results revealed significant correlations between phosphorus species in sediments from the lake with two extractable principal component species (PCs) and five selectable cluster levels allowing interpretation of possible origins of phosphorus loading and the release of phosphorus. Furthermore, available remediation measures were briefly assessed for the lake with consideration of its distinctive environmental features.
Based on the techniques of sequential extraction and X-ray powder diffraction(XRD) ,the distribution characteristics of phosphorus speciation were investigated in 13 sediment samples from Lake Hongfeng,an important drinking water source for Guiyang with a typical karstic limestone environment.The total phosphorus(TP) concentrations in the sediments ranged from 973.36 to 2334.18 mg/kg with a mean concentration of 1635.87 mg/kg(dry weight) ,and it was evident that the phosphorus level in the sediments was high compared with other eutrophic lakes such as Lake Chaohu and Lake Xihu.The results of the two methods,sequential extraction and XRD,demonstrated the presence of different phosphorus species in the lake sediments.Being compatible with local geophysical characteristics,the results of sequential extraction techniques indicate that the average percentages of dissolved phosphorus(DP) ,aluminum-bound phosphorus(Al-P) ,iron-bound phosphorus(Fe-P) ,calcium-bound phosphorus(Ca-P) and organic phosphorus(OP) in the sediments were 0.40%,7.06%,5.07%,45.48%and 38.49%,respectively.Notably,the concentrations of inorganic phosphorus(IP) were higher than those of OP,and the IP consisted primarily of Ca-P.The high concentrations of Ca-P may temporarily control the release of phosphorus from the sediments because it is a relatively stable,inert and non-bioavailable phosphorus fraction.The results of XRD analysis indicated that,among phosphorus species,AlPO4 was found in all sediment samples at relatively high concentrations.Moreover,the TP concentrations in the sediments were high;thus the release potential and bioavailability of phosphorus in the sediments was important.Further statistical analyses of the results revealed significant correlations between phosphorus species in the sediments with two extractable principal components and four selectable cluster levels allowing interpretation of possible origins of phosphorus loading and transformation mechanisms of phosphorus species.Furthermore,available remediation measures were
JIANG CuiHong WU Di HU JiWei LIU Feng HUANG XianFei LI CunXiong JIN Mei
