Guo Laodong, Lehner Jaime K, White Daniel M, Garland D Sarah
International Arctic Research Center, University of Alaska Fairbanks, Fairbanks, AK 99775, USA.
Water Res. 2003 Mar;37(5):1015-22. doi: 10.1016/s0043-1354(02)00443-8.
Water samples were collected in July 2001 from the Chena River in central Alaska. The natural organic matter (NOM) was size fractionated into particulate (POM,>0.45 microm), colloidal (COM,1kDa-0.45 microm) and dissolved (DOM,<1k Da) organic matter fractions, using filtration and ultrafiltration. The size-fractionated organic matter was then analyzed for organic carbon (OC) and nitrogen (N), isotopic (delta13C and delta15N) and molecular composition, using continuous flow isotope ratio mass spectrometry and pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). Results of phase partitioning showed that, on average, about 6% of OC and 16% of N occurred in the form of POM while 66% of OC and 57% of N occurred in the form of COM, and 28% of the OC and 27% of the N were in the DOM form. Organic matter in the river water was found to be highly heterogeneous in terms of chemical composition and isotopic signatures. The C/N ratio was as low as 16+/-1 in the POM (n=2) to as high as 48+/-1 in the COM (n=3) and 38+/-4 in the DOM (n=3), suggesting a diagenetically younger POM. Values of delta13C increased with decreasing size, varying from -29.59+/-0.45% in the POM to -27.47+/-0.06% in the COM to -16.93+/-0.08% in the DOM. In contrast, values of delta15N decreased with decreasing size, from 2.64% in POM to 1.64% in COM to 1.33% in DOM. These results, together with radiocarbon measurements, suggest a preferential decomposition of lighter C isotope (12C) and heavier N isotopic (15N) from POM to COM to DOM. Results of py-GC/MS showed that the percentage of polysaccharides decreased with decreasing size, further supporting a degradation pathway of NOM from POM to COM and DOM in Chena River waters. More studies are needed to examine the seasonal and spatial variations of size-fractionated organic matter.
2001年7月从阿拉斯加中部的切纳河采集了水样。利用过滤和超滤技术，将天然有机物（NOM）按粒径分为颗粒态（POM，>0.45微米）、胶体态（COM，1千道尔顿 - 0.45微米）和溶解态（DOM，<1千道尔顿）有机物组分。然后，使用连续流同位素比率质谱仪和热解 - 气相色谱/质谱仪（Py - GC/MS）对按粒径分级的有机物进行有机碳（OC）、氮（N）、同位素（δ13C和δ15N）及分子组成分析。相分配结果表明，平均而言，约6%的OC和16%的N以POM形式存在，66%的OC和57%的N以COM形式存在，28%的OC和27%的N以DOM形式存在。发现河水中的有机物在化学成分和同位素特征方面高度不均一。POM中的C/N比低至16±1（n = 2），COM中高达48±1（n = 3），DOM中为38±4（n = 3），表明POM在成岩作用上更年轻。δ13C值随粒径减小而增加，从POM中的 - 29.59±0.45‰变化到COM中的 - 27.47±0.06‰，再到DOM中的 - 16.93±0.08‰。相反，δ15N值随粒径减小而降低，从POM中的2.64‰降至COM中的1.64‰，再到DOM中的1.33‰。这些结果与放射性碳测量结果一起表明，较轻的碳同位素（12C）和较重的氮同位素（15N）从POM到COM再到DOM存在优先分解现象。Py - GC/MS结果表明，多糖的百分比随粒径减小而降低，进一步支持了切纳河水中NOM从POM到COM再到DOM的降解途径。需要更多研究来考察按粒径分级的有机物的季节和空间变化。
