Quality transformation of dissolved organic carbon during water transit through lakes: contrasting controls by photochemical and biological processes
Quality transformation of dissolved organic carbon during water transit through lakes: contrasting controls by photochemical and biological processes
复制标题
DOI：
10.5194/bg-15-457-2018
复制
发表时间：
2018-01-24
期刊：
影响因子：
4.9
通讯作者：
Karlsson, Jan
中科院分区：
文献类型：
--
作者：
Berggren, Martin;Klaus, Marcus;Karlsson, Jan
溶解有机碳（DOC）可能会被移除，转换，或通过湖泊的水运输过程中添加，导致DOC组成和色素（颜色）的变化。然而，这些变化的过程为基础的理解是不完整的，特别是对于源头湖泊。我们假设，因为异养细菌优先消耗无色DOC，而光化学处理去除有色组分，DOC颜色的整体变化后，通过湖泊的水通道取决于这两个过程的相对重要性，相应地。为了验证这一假设，我们结合实验室实验与实地研究在九个北方湖泊，评估不同的DOC衰减过程（生物或光化学）的相对重要性和损失的颜色在水过境时间（WTT）通过湖泊。我们发现，从光衰减的影响占主导地位的DOC质量的变化在epilimnia相对清晰的源头湖泊，导致系统和选择性的彩色DOC的净损失。然而，在高度着色的棕色水湖泊（420 nm处的吸光度> 7 m（-1））的生物过程占主导地位，并没有系统的颜色损失和WTT之间的关系。此外，在原位数据和黑暗的实验支持我们的假设上的选择性微生物去除nonpigmented DOC，主要是低分子量，导致持久的水色在这些高度着色的湖泊。我们的研究表明，棕色的源头湖泊可能不符合通常报道的模式，选择性地去除淡水中的有色成分，DOC可以显示出持续的色素沉着程度时，通过这些湖泊过境。
Dissolved organic carbon (DOC) may be removed, transformed, or added during water transit through lakes, resulting in changes in DOC composition and pigmentation (color). However, the process-based understanding of these changes is incomplete, especially for headwater lakes. We hypothesized that because heterotrophic bacteria preferentially consume noncolored DOC, while photochemical processing removes colored fractions, the overall changes in DOC color upon water passage through a lake depend on the relative importance of these two processes, accordingly. To test this hypothesis we combined laboratory experiments with field studies in nine boreal lakes, assessing both the relative importance of different DOC decay processes (biological or photochemical) and the loss of color during water transit time (WTT) through the lakes. We found that influence from photo-decay dominated changes in DOC quality in the epilimnia of relatively clear headwater lakes, resulting in systematic and selective net losses of colored DOC. However, in highly pigmented brown-water lakes (absorbance at 420 nm > 7 m(-1)) biological processes dominated, and there was no systematic relationship between color loss and WTT. Moreover, in situ data and dark experiments supported our hypothesis on the selective microbial removal of nonpigmented DOC, mainly of low molecular weight, leading to persistent water color in these highly colored lakes. Our study shows that brown headwater lakes may not conform to the commonly reported pattern of the selective removal of colored constituents in freshwaters, as DOC can show a sustained degree of pigmentation upon transit through these lakes.