Optical Characterization And Size Distribution Of Dissolved Organic Matter In The Jiulong River

Riverine dissolved organic matter(DOM)is an important source of marine organic matter,its biogeochemical process has an important impact on the global carbon cycle.In this study,the optical characteristics of DOM,colloid organics and its size distributions of the three main tributaries of Jiulong river.The main conclusions were:(1)DOC concentrations were 1.24±0.21 mg/L?1.87·0.34 mg/L?2.29±0.57 mg/L in North brook,West brook,and South brook,respectively.Four fluorescent components were identified using PARAFAC in our study with three humic-like(Cl,C2 and C3)and one protein-like(C4).(2)Humic-like was the dominant component in Jiulong River((Cl+C3)%>52%),indicating that the main source of DOM in Jiulong is terrestrial.The DOC yield of North brook(3.7g-C/m2/a),West brook(2.8g-C/m2/a)and South brook(1.7g-C/m2/a)decreased successively.No significant seasonal differences of DOM content as well as optical characterizations including SUVA254,S275-295,FIX and BIX had been found,indicating a state of chemostats in the downstream of Jiulong river.This chemical steady-state is the result of the balance of DOM source and removal process in the downstream.In addition,the "chemostat" state is exacerbated by the inflow of tributaries and damming of the basin.CDOM flux can be used to indicate DOC flux in Jiulong river,and the estimated error is less than 10%.(3)A better significant positive relationship between LMW DOC and LMW a254 than that of HMW DOM,and much larger percentage of non-chromophoric DOM in HMW(48±17%,35±18%and 47±23%in North brook,West brook,and South brook,respectively)than LMW(23±10%,20±11%and 12±5%,respectively)indicating heavily photodegradation(4)Biological indexes(BIX)of low molecular weight dissolved organic matter(LMW DOM)with an average of 1.00±0.26,0.91±0.22 and 0.86±0.19 in North brook,West brook,and South brook,respectively were significant higher than that of high molecular weight(HMW DOM,0.74±0.17,0.77±0.22 and 0.73±0.11 in North brook,West brook,and South brook,respectively),reflecting that LMW DOM contains more refractory organic compounds modified by microorganism.HMW DOM SR(0.83±0.23,0.68±0.16 and 0.79±0.155 in North brook,West brook,and South brook,respectively)was significant higher than that of LMW DOM,resulting from biological degradation of LMW DOM.(5)The colloidal CDOM in Jiulong River is mainly composed of 1-8nm components,and the components in North brook,West brook,and South brook are 1.2±0.4 cm-1 ·min,1.8±0.5 cm-1· min and 2.3±0,06 cm-1·min,respectively.And the components of 8-15 nm in North brook,West brook,and South brook were 0.51±0.35 min·cm-1?0.77±0.53 min·cm-1? 0.69±0.42 min·cm-1,respectively.The components of>15 nm in North brook,West brook,and South brook are 0.55±0.58 min cm-1?0.92±0.68 min·cm-1?0.73±0.85 min·cm-1,respectively.(6)The colloidal size distribution of different fluorescence components was diverse,which was related to the source of different fluorescence components.The C1 component was dominant by 1-8 nm colloidal,percentage of[C1]1-8 nm were 78±12%,76±14%and 85±9%for North brook,West brook,and South brook,respectively.C2 was also dominated by 1-8 nm colloidal component as well,and the percentage of[C1]1-8nm were 58.3±15.5%,60.8±13.0%and 64.0±12.9%,respectively.The ratio of>15nm to the total integral area of the colloidal size spectrum of C3 component was 66 12%,62 15%and 61 9%for North brook,West brook,and South brook,respectively.The ratio of>15nm to the total integral area of the colloidal size spectrum of C4 component was 69 17%,64 20%and 73 16%,respectively.