Spatial And Temporal Distribution Characteristics Of Dissolved Organic Matter In Zhoucun Reservoir

Zhoucun Reservoir is located in the upper Xijia River of Huaihe river basin,in which climate belongs to the subtropical continental monsoon climate in the mid-latitudes,and it is an important water source of drinking water in Zaozhuang.Inder to explore the seasonal variations and the possible source of dissolved organic matter in water source of the subtropical zone,24 surface water samples were collected during August and December,2015 from Zhoucun Reservoir,compared with 14 surface water samples collected from Jinpen Reservoir during December,2015.In addition,10 samplings were carried out from different depths of Zhoucun Reservoir,Zaozhuang City.The dissolved organic matter was continuously monitored in situ from July 2015 to June 2016.The main conclusions are as follows:(1)Based on the characteristics of CDOM absorption coefficient and the distribution of samples,Zhoucun Reservoir could be divided into Storage port,Transition region and Main reservoir area respectively.The absorption coefficient of CDOM had a decrease process from storage port to main reservoir aera,while the S value exhibited an increasing trend,which means the sources and components of CDOM of each area were different.Significant negative correlation relationships were showned between the value of S240~500 and a(355),a*(355),which is helpful to establish the estimation model of a(355).At the same time,a(355)and aph(440)had very significantly positive linear correlation,which indicated that the metabolism of phytoplankton was a potential source of CDOM in summer.(2)Three fluorescent components were identified by using excitation emission matrix fluorescence spectroscopy-parallel factor analysis technique,including fulvic-like(C1:260,350/420 nm),protein-like(C2:280/360 nm)and humic-like(C3:270,390/530 nm)components.The spatial distribution of each component was even,but the total fluorescence intensity in storage port was relatively high.The fluorescence characteristic indices(FI,BIX,HIX and ?:? of DOM)were calculated and analyzed,combined with the results of principal component analysis,we could find that the DOM of Zhoucun Reservoir had a strong autochthonous contribution which contribution rate to the DOM had been reached 70.86%.However,the contribution of runoff could not be ignored.(3)Three fluorescent components of DOM in Zhoucun Reservoir and Jinpen Reservoir were identified by fluorescence ultraviolet-visible(UV-vis)and excitation-emission matrix spectra,including fulvic-like component(C1:260,350/420 nm),protein-like(C2:280/360 nm)and humic-like(C3:270,390/530 nm).But the fluorescence intensity and the proportion of its composition were significantly different.Combined with the comparision of fluorescence index,biological index,humification index and the freshness index,the results are as follows: in winter,the main source of DOM was autochthonous in Zhoucun Reservoir where the land-use type was cultivated,livestock and residential land,and the DOM of Jinpen Reservoir dominated by forest system had a higher terrigenous contribution,respectively.It can be found that the hydrological conditions of the mixed reservoir and the characteristics of the coastal ecological environment would affect the DOM in the water body.(4)Using parallel analysis,three fluorescent components of DOM in Zhoucun Reservoir were identified from the vertical water samples,including fulvic-like component(C1:260,350/420 nm),protein-like(C2:280/360 nm)and humic-like(C3:270,390/530 nm).There was no obvious stratification in spacial distribution during the whole year,but in the time distribution,we could notice that the fluorescence intensity of humic-like was largest in summer;However,the fluorescence intensity of fulvic-like component was largest in autumn;The content of protein-like was the lowest in winter.In addition,the concentrations of chlorophyll,dissolved organic carbon,nitrogen and phosphorus nutrients and all kinds of carbohydrate concentrations were analyzed from the vertical water samples.The results showed that the concentration of dissolved organic carbon was related to the concentration of nitrate nitrogen,total nitrogen and dissolved total nitrogen.On average,Carbon of dissolved polysaccharides and dissolved monosaccharides accounted for 7.2% and 3.6% of the dissolved organic carbon.The concentration of chlorophyll and dissolved organic carbon had no significant correlation,showing that the sources of dissolved organic carbon and carbohydrates were not only from phytoplankton,but also from runoff.