A Method Of Determining Carbon Isotope Of Dissolved Organic Carbon And Application In Jiulong River

Carbon cycle playing a key role in studying global biogeochemical cycle, it relates to the atmosphere, terrestrial biosphere, hydrosphere and lithosphere. Rivers as the most important connection between oceans and land,which are two carbon reservoir on the earth,it is the main approach for transported the carbonaceous material in terrene to the ocean.Therefore, understanding the carbon cycle in rivers for the carbon in biogeochemical cycle would be a important significance,and stable isotope techniques provides a technology method for studying source of carbon in rivers.This paper research a method for simultaneous determination of Dissolved Organic Carbon(DOC) content and carbon isotope(δ13CDOC)——Wet Oxidation-Mass Spectrometry.It uses routine hydrochemical(wet oxidation),with existing online sampling preparation apparatus(Gas Bench II) and stable isotope mass spectrometer(IRMS) in laboratory,for measuring DOC content and δ13CDOC. Before we apply the method to Jiulong River including West River,North River and Estuary,we are prioritized to measuring and analysing the stability in different conditions for Wet Oxidation-Mass Spectrometry. And then we determinate DOC content and δ13CDOC in surface water in main stream(West River and North River) and Estuary of Jiulong River, while discussed the variation and sources of DOC in main stream and estuary of Jiulong River.Following the conclusions:1. The experimental show using Wet Oxidation-Mass Spectrometry to measuring isotope of blanks and standard substances of DOC has a stable result, and indicating that it can be applied to measure isotope of DOC.The method in conditions of 1.0 ml oxidant and 100℃ oxidation temperature for measuring standard substances of DOC has a better stability of carbon recoveries and carbon isotope, but due to the blank,which affected carbon isotope to appear obviously fractionation.With concentration of standard samples increasing,carbon isotope is closed to its true value,but carbon recoveries depressed.2. Seasonal variation of DOC content in surface water in West River show the value has higher in Spring(5.56 mg/L) than in Summer(3.38 mg/L), and δ13CDOC shows high value in Spring(-13.11‰) than in Summer(-15.38‰);The spatial variation show there were a higher DOC content and values of δ13CDOC in downstream than the upstream in Spring, and there were no clear variation tendency in Summer. Seasonal variation of DOC content in surface waters in North River shows the value in Spring(2.18 mg/L) has less than in Summer(4.85 mg/L),but value of δ13CDOC shows Spring(-12.91‰) less than Summer(-12.37‰);The spatial variation show there were a higher DOC content in upstream than the downstream in Spring and Summer,but it raised again near estuary.The value of δ13CDOC from upstream to the downstream was decreasing in summer, and there was no clear variation tendency in Spring.3. Seasonal variation of DOC content in surface water in Estuary of Jiulong River show the value in Spring(5.13 mg/L) has less than in Summer(6.68 mg/L),and values of δ13CDOC show Spring(-12.38‰) has less than Summer(-8.74‰); DOC content and value of δ13CDOC show the spatial variation there were increasing from upstream to the downstream in Spring and Summer, which had a high value closed to the marine.