Bioavailability Of Dissolved Organic Matter In Dongping Lake

Dissolved organic matter（DOM）is a combination of ecological functions,and is also the most important carbon source of water.The migration,transformation and regeneration of organic elements such as carbon,nitrogen,and phosphorus in DOM and the chelation or polarity of various functional groups with pollutants affect the migration,transformation,and bioavailability of organic pollutants in lake ecosystems.DOM in inland lakes is mainly affected by terrestrial input and biodegradation release.we found that the decomposition of submerged plants and phytoplankton in macrophytic lakes was accompanied by the release of a large number of organic pollutants,the microbial degradation in this process significantly impacts on the structure and properties of DOM.Meanwhile,organic carbon,as a mobile part of DOM,will produce and release greenhouse gases,such as methane（CH₄）and carbon dioxide（CO₂）through microbial respiration with changes of content for protein-like and humic-like substances in DOM in the process of microbial degradation.This process will affect the migration and transformation of organic matter in the ecological environment and the carbon cycling function of lake.Based on the above backdround,by using field survey,sampling,indoor simulation experiment,and other methods,the characteristic and spatial difference of DOM in compositions,sources,and microbial degradation in Dongping Lake during dry seasons and wet seasons and variation of CH₄content,before and after DOM degradation were studies to provides scientific basis for further understanding the biogeochemical cycle of DOM in shallow macrophytic lakes.The main research conclusions are as follows:1.Three-dimensional fluorescence spectra showed significant differences in the fluorescence peaks of DOM in different hydrological periods.The fluorescence intensity of DOM in wet season was significantly stronger than dry season,and the exogenous protein-like substances contributed significantly to DOM in the entrance into Dongping Lake.Fluorescence intensity in wet season was significantly higher than that in dry season（t<0.001）,and the content of tyrosine-like components was higher than that of tryptophane-like components in dry and wet seasons,indicating that tyrosine-like components were the main contributors of DOM in Dongping Lake.In dry season,high and low values of the total fluorescence intensity for DOM were exhibited in north and south of the lake spatially,respectively,which was mainly affected by internal input.During the wet season,the lake was heavily polluted by the input of Dawen River and the Laohu Wharf,and production,and planting land were the fundamental reasons for this phenomenon.2.The tyrosine-like components C4 and C2 in DOM is the main contributors of Dongping Lake during the two periods.The result suggested that tyrosine-like substances play an important role and the content of protein-like and humic-like substances changed in the microbial degradation activity in Dongping Lake,which confirmed from another aspect that the microbial dark degradation process would impact the structure of DOM.3.A large spatial difference was found in the concentration of CH₄from the surface water of Dongping Lake.The concentration of CH₄in the northern reed area was the highest,and the minimum value of CH₄were located in the southern part of the lake,which may be related to temperature,substrate concentration,and other factors.The increase of in SUVA in Dongping Lake waters indicated the increase of in humification degree of DOM.There were abundant plankton in the water along the northern and southern shores of the lake,and the decay and degradation of phytoplankton was the root cause of the increase of DOM organic matter in the water.CH₄concentration of surface water of most of the samples showed an upward trend,indicating that the overly water of Dongping Lake also has a certain potential for greenhouse gassed emission.