Autochthonous origin of semi-labile dissolved organic carbon in a large monomictic lake (Lake Biwa): carbon stable isotopic evidence
Autochthonous origin of semi-labile dissolved organic carbon in a large monomictic lake (Lake Biwa): carbon stable isotopic evidence
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DOI：
10.1007/s10201-009-0299-z
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发表时间：
2010-08-01
期刊：
影响因子：
1.6
通讯作者：
Nagata, Toshi
中科院分区：
文献类型：
--
作者：
Maki, Koh;Kim, Chulgoo;Nagata, Toshi
半不稳定溶解有机碳(DOC)在大型淡水湖碳的迁移和亚极磁再矿化过程中起着重要作用。然而，湖泊中半不稳定DOC的来源仍然不清楚。本研究使用碳稳定同位素方法研究了原地和异地来源对半不稳定DOC的相对贡献。测定了大面积(表面积674 km(2)，最大深度104m)琵琶湖DOC浓度和碳稳定同位素比值(C-13)的垂直变化和季节变化。DOC的增量C-13(增量C-13-DOC)在层结期间的急剧垂直梯度[表层和下层的平均+/-A标准差(SE)分别为-25.5+/-A0.1和-26.0+/-A0.0a欧度]表明富含C-13的DOC在表层积累。垂直混合解释了倾覆期间在整个水柱中测量到的增量C-13-DOC的中间值(-25.7+/-A 0.0a欧洲度)。在层结过程中，表层DOC浓度和增量C-13-DOC均降低，表明富含C-13的DOC具有选择性再矿化作用。利用双组分混合模型，我们估算出半不稳定DOC的C-13值为-22.2+/-A 0.3a欧度，接近丰产季节表层沉积物中颗粒有机碳的C-13值(-22.7+/-A 0.7a欧罗度)，但远高于河水中的C-13-DOC增量(-26.5+/-A 0.1a欧罗度)。半不稳定的DOC似乎主要是原生的，由浮游生物群落在旺季产生。半不稳定DOC的产生和再矿化之间的时空不耦合表明，次磁耗氧量可能受到前一年生产季中上层初级生产力的影响。
Semi-labile dissolved organic carbon (DOC) plays an important role in the transport and hypolimnetic remineralization of carbon in large freshwater lakes. However, sources of semi-labile DOC in lakes remain unclear. This study used a carbon stable isotope approach to examine relative contributions of autochthonous and allochthonous sources to semi-labile DOC. Vertical and seasonal variations in the concentration and carbon stable isotope ratio (delta C-13) of DOC were determined in large (surface area 674 km(2); maximum depth 104 m), monomictic Lake Biwa. A sharp vertical gradient of delta C-13 of DOC (delta C-13-DOC) during the stratification period [mean +/- A standard error (SE) -25.5 +/- A 0.1 and -26.0 +/- A 0.0aEuro degrees in the epi- and hypolimnion, respectively] indicated the accumulation of C-13-rich DOC in the epilimnion. Vertical mixing explained the intermediate values of delta C-13-DOC (-25.7 +/- A 0.0aEuro degrees) measured throughout the water column during the overturn period. Both DOC concentration and delta C-13-DOC decreased in the hypolimnion during stratification, indicating selective remineralization of C-13-rich DOC. Using a two-component mixing model, we estimated the delta C-13 value of semi-labile DOC to be -22.2 +/- A 0.3aEuro degrees, which was close to the delta C-13 of particulate organic carbon collected in the epilimnion during productive seasons (-22.7 +/- A 0.7aEuro degrees) but much higher than the delta C-13-DOC in river waters (-26.5 +/- A 0.1aEuro degrees). Semi-labile DOC appeared to be mainly autochthonous in origin, produced by planktonic communities during productive seasons. The spatiotemporal uncoupling between production and remineralization of semi-labile DOC implies that hypolimnetic oxygen consumption may be affected by pelagic primary production during productive seasons of the preceding year.