Research On Characteristics Of Dissolved Organic Matter(DOM) In Urban Storm Sewer Sediments

Storm sewer,which acts as the middle part of runoff and final receiving water,is not only the city's major drainage channels and the important medium for urban water cycle,but also an important way to take urban nonpoint source pollution into the natural water bodies.Large quantities of pollutants in runoff could be deposited in storm sewers and deteriorated under the special environment;additionally,the pollutants in sediments could be re-released into water bodies under the erosion action of overlying water,leading to the damage of water environment.The characteristics of distribution,occurrence,and contamination risk of many pollutants(heavy metals,organic nitrogen,phosphorus etc.)in sewer sediments have been analyzed by lots of domestic and foreign scholars.However,nearly nothing is reported as to the dissolved organic matter(DOM)in storm sewer sediments.Dissolved organic matter is a kind of mixture with complex chemical structure characteristics,and the components and structural characteristics of DOM in different environment are all very different.In addition,DOM also plays an important role in the transmission and conversion of heavy metals and other environmental contaminants.Therefore,this study focused on the sources,components,structure of DOM in storm sewer sediments in different functional regions of Beijing.Besides,the polluted station of heavy metals in storm sewer sediments are evaluated,and the influence of dissolved organic matter on heavy metals(Cu)at the distribution in solid and liquid are also cleared.Ultrafiltration method is used to separate the DOM into different molecular weight,and the basic characteristics of different molecular weight DOM are also analyzed.All the analytical results are listed below:(1)The differences of human activities and urban catchment materials made obvious different contribution to the sediment DOM in storm sewers.the sediment DOM in storm sewers exhibit both autochthonous and allochthonous component character,microbial activities play an important role in accumulation of the sediment DOM,and a lot of protein-like substances are produced.(2)In each functional area,the polluted levels of Cu,Zn are much higher than other heavy metals,and Pb pollution is mainly reflected in the traffic area.The potential ecological risk composite index(Hakanson,RI)shows that the overall level of heavy metal pollution in traffic area is much higher than other regions,which belongs to the medium level;Cd and Cu made more contribution to the RI of heavy metals.Besides,DOM shows great correlation with Cu,Pb,Zn,but do not reflect the significant correlation with Cd and Cr.(3)DOM plays a very important role on the distribution of Cu between solid and liquid phase.Organic matters made great contribution to the transmission of Cu from water to sediment(87~96%),and the contribution of mineral particles is merely 2~9%.More Cu ions could be fixed in the sediments by DOM.On the other side,Cu could also be re-released into water by DOM,especially the DOM with lots of protein-like substances.(4)DOM with lower molecular weight(<3k Da)in sediments accounts for about 60~70% of the total,which is mainly consistent of protein-like substances,and humic-like substances are mainly concentrated in the high molecular weight(> 10 k Da)region.Additionally,lower molecular weight DOM could be well complexed with Cu,especially the stability and binding capacity of Cu and DOM in <1k Da part is the most stable and largest in all of the regions.