| Dissolved organic matter (DOM) is operationally defined as the fraction of organic carbon that passes through a 0.45u,m filter. The 0.45um definition is an arbitrary cut-off, which is based on the historical availability of this filter pore size. DOM plays a central role in aquatic environment. It is an important ligand and sorbent. The importance in aquatic chemistry and aquatic ecosystems is expressed by altering the bioavailability of metals, organic contaminants such as ployaromatic hydrocarbons (Driscoll et al. 1990; Oris et al., 1990), as well as increasing the attenuation of visible and ultraviolet radiation and contributing to the natural acidity of waters (Wetzel, 1983; Driscoll et al., 1989). Both the concentration as well as the chemical and physical nature of DOM in lakes can also greatly influence the productivity and structure of aquatic ecosystems.DOC is approximately 50% carbon by weight; the remaining elemental composition comprises oxygen (40%), hydrogen (5%), nitrogen (0.5% to 6.5%), phosphorous (<1.0%), sulfur (<1.0%) and ash (1.2-5.0%) (Thurmanl985). DOM is a complex organic compound. The humic substance occupied 50-80 percent of DOM, which was divided into three parts, including humic acid, fulvic acid and humin. The nonhumic substances contain hydrocarbons, amino acid, chlorophyll, algae, phenolic, et al. (Thurman, 1985).Some metal ion and minim element always combine with DOM. The effect of these elements in water is influenced by their molecular weight. The molecular weight of DOM within lakes provides valuable insight into the potential of a particular system to reduce the level of contaminant toxicity. By elucidating the relationship between the structural character or molecular size of DOC and the role it plays in the environment, we can begin to understand, and further, to model the response of freshwater lakes and streams to anthropogenic stresses and circumstances that may arise from climate change.Lake Hongfeng and Baihua are the two large manual reservoirs, which situatedon the Guizhou Plateau. The two reservoirs are the main sources of drinking water in Guiyang. The source of water comes from some streams in drainage area. By determinate the hydrological environment, we discussed the factors that affected the variation of molecular weight distribution of dissolved organic matter, including the abundance of dissolved oxygen, temperature of water, pH value, chlorophyll a, illumination, and bloom of plankton, the origin of dissolved organic matter, the contaminate by human. This research has determined the molecular weight distribution of DOM in Lake Hongfeng and Baihua by HPSEC Some conclusions were obtained.1 The optimal experimental condition was collected, including the mobile phase of 0.03M NaCl and 0.002 phosphate buffer, the pH value of 6.8, the ion strength of 0.034 mol/L, the wavelength of 254 nm.2 The DOM molecule with molecular weight higher 3000Da occupied the largest part of DOM, account for higher 90 percent. By the peak area of each fraction, we divided the DOM into three fractions with different molecular weight. The large fraction with molecular weight higher than 2000 Da occupied 35% to 68% of total DOM. The medium fraction with 2000Da>MW>1000Da consisted of 27 to 57 percent of total DOM. And small fraction with molecular weight smaller than lOOODa only occupied 3 to 31 percent of total DOM.3 The content of DOC was influenced by weather. The content of DOC in upper water is higher than that in deeper water in rain season. The carbon content remains relative constant in water column in dry season. The change of carbon content of each fraction is similar with that of the total DOC. The content of DOC also changes with season. It is higher in rain season than that in dry season. But the difference between the two lakes is not remarkable.4 The averaged molecular weight is also influenced by climate. It becomes higher with depth of water column in rain season. And it remains relative constant in dry season. The variable with season is opposit...
|
PDF Full Text Request