Investigation On Distribution Of Organic Matter And Its Complexation With Heavy Metals In Sediments Of Different Ecological Lakes In China

Eutrophication is one of serious water pollution problems that occur throughoutthe world. In China, some shallow lakes along the middle and lower reaches of theYangtze River are in the state of eutrophication. Organic matter enrichment is theimportant feature in lake eutrophication. In sediments, organic matter is the key factorto control the environmental behaviors of heavy metal pollutant because complexationbetween heavy metals and organic matter controls heavy metal migration andbiological toxicity. Therefore, the investigation on distribution of organic matter andits complexation with heavy metals in different ecological lakes is important to fightwater pollution.This study is one part of a key project (2008CB418204) financed by ourgovernment. Characters, structures and sources of dissolved organic matter (DOM) inthree different ecology lakes (Taihu Lake, Nansihu Lake and Baiyangdian Lake) wereanalyzed, respectively, using UV spectroscopy, elemental analysis, FTIR,1HNMRand fluorescence spectra. The main findings are as following:1.The water quality is worse than that required by Grade V in Taihu Lake,Nansihu Lake and Baiyangdian Lake. The concentrations of total nitrogen (TN) andtotal phosphorus (TP) are high in water and sediment in Nansihu Lake. This resultshows that it is important to control internal pollution sources. Under higher nutrientconcentration conditions, the mass ratio of nitrogen to phosphorus (N/P) impacts onlake eutrophication. Phosphorus is a limited factor of the eutrophication features inTaihu Lake and Baiyangdian Lake. Nitrogen and phosphorus are limited factor inNansihu Lake. Some measures should be carried out to reduce nitrogen andphosphorus pollutants, which could ease the eutrophic process in Taihu Lake,Nansihu Lake and Baiyangdian Lake. In addition, sedimentary heavy metal pollutionwas also studied through Tessie extraction procedure. The index of geo-accumulation(Igeo) was applied to evaluate the heavy metal pollution in the sediment. Our results show that Cu pollution is serious in the Taihu Lake, in Nansihu Lake and BaiyangdianLake. Zn mainly exists in residual fraction and the iron and manganese oxidationstate fraction ranks the second. Cu mainly exists in residual fraction and the organicthe sulfide phase fraction ranks the second. The results also reveal that Cu and Zn areeasily mobile and could bring ecological risk to the water ecological system.Anthropogenic activities contributed to potential sources of heavy metals.2.Distribution of total organic matter (OM), light fraction organic matter(LFOM),heavy fraction organic matter(HFOM),labile organic matter(LOM) and DOM in thesediments from three different shallow lakes (Taihu Lake, Nansihu Lake andBaiyangdian Lake ) were investigated by using physical separation methods. Theresults show that the light fraction organic matter (LFOM) is significantly low in allthe sediments. Heavy fraction organic matter (HFOM) is the dominant class amongthe organic matter compositions in Taihu Lake, Nansihu Lake and Baiyangdian Lakesediments. These results demonstrate that the persistent organic compounds accountfor most of the organic matters, and that light fraction organic matter was completelydecomposed.3.Different fractions of DOM have different origin. The hydrogen/carbon andoxygen/carbon ratios decrease from sanitary area, aquatic area, culture area to dirtywater area. These results suggest that the less the ratio, less the polarity, the morestability. The analyses of FTIR and1HNMR also show that DOM of different sourcehas different structural characterization. DOM in culture area and in dirty water iscomposed of the aromatic carbon, aliphatic amines, carboxylic acid dimmers andalkyl chain hydrocarbon material.4.DOM in Taihu Lake, Nansihu Lake and Baiyangdian Lake sediments were alsoinvestigated by using fluorescence spectroscopy. Fluorescence index (f450/500) could beused to distinguish sources. (f450/500) values ranged 1.4-1.9 in Taihu Lake, NansihuLake and Baiyangdian Lake sediments. This result indicated biology sources as wellas land sources of sediments DOM. Fluorescence finger print technique was used tocharacterize dissolved organic matter (DOM) in sediments from different sources.Two types of DOM fluorescence signals were observed in sediments: humic-like fluorescence and protein-like fluorescence. The intensities of both of protein-likefluorescence distinctly increase in culture area and in dirty water area. The values ofr(B,C) is 1 in sanitary area. The values of r(B,C) is 1.5-2.5 in culture zone and dirtywater area, revealing that this index is a indicator degree of lake contamination.Fluorescence finger print technique is potential tool to determine the sources of DOMin polluted lakes.5.Fluorescence spectrum technique has advantages of high sensitivity, andquick-and-easy detection and has widely applied to characterize the dissolved organicmatter (DOM). For better understanding the fluorescence characteristics of DOM inBaiyangdian Lake of China, fluorescence emission spectroscopy andthree-dimensional excitation emission matrix fluorescence spectroscopy (3DEEM)were used. Fluorescence quenching titration and1H NMR were used to investigate theinteraction between Cu (â…¡) and DOM. The1H NMR results show that DOM inBaiyangdian Lake is mainly composed of large amount of carbohydrate. Influorescence spectra obtained in our study, two fulvic acid-like fluorescence peaks(peak A and peak C) and protein-like (peakB) were observed. Compared with visiblefulvic-like, protein-like fluorescence intensity is high. The intensity for individualpeak A, B and C decreases as concentrations of Cu (â…¡) increase. DOM-Cu (â…¡)complexation constants and1H NMR suggest that the fluorescent groups interactmore strongly with Cu (â…¡) .