Soil Aggregates as a Source of Dissolved Organic Carbon to Streams: An Experimental Study on the Effect of Solution Chemistry on Water Extractable Carbon
Soil Aggregates as a Source of Dissolved Organic Carbon to Streams: An Experimental Study on the Effect of Solution Chemistry on Water Extractable Carbon
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DOI：
10.3389/fenvs.2019.00172
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发表时间：
2019-11-07
影响因子：
4.6
通讯作者：
Shanley, James B.
中科院分区：
文献类型：
--
作者：
Cincotta, Malayika M.;Perdrial, Julia N.;Shanley, James B.
在过去的二十年里，北半球的源头溪流显示出溶解有机碳（DOC）的数量增加，与酸沉积减少相一致。降水组成与水体DOC之间机制联系的确切性质在文献中仍存在广泛争议。我们假设土壤团聚体是河流水中DOC的主要来源，并且有机质丰富的河岸土壤中DOC的释放量大于山坡土壤。为了验证这些假设，我们从佛蒙特州东北部受酸影响的Sleepers河研究流域的两个主要景观位置（山坡和河岸地带）收集了土壤。我们用不同离子强度（IS）和成分的溶液来模拟土壤溶液的变化。通过荧光光谱技术监测土壤粒径、团聚体结构和组成、渗滤液DOC浓度、溶解有机质（DOM）特征和生物利用度趋势的动态变化。在低IS溶液中，可提取的DOC浓度明显较高，粒径（激光衍射）明显较小，扫描电镜观察有机物质从矿物颗粒中分离出来。此外，与相同IS的Ca2+溶液相比，Na+溶液中的DOC浓度更高。这些影响是由于在减少的IS溶液中扩散双层导致的聚集体分散和二价阳离子减少的桥接。景观位置影响DOC的质量，但不影响DOC的数量。总体而言，这些结果表明土壤团聚体可能是临界带输入（即降水）与河流输出之间的重要联系。
Over the past two decades, headwater streams of the northern hemisphere have shown increased amounts of dissolved organic carbon (DOC), coinciding with decreased acid deposition. The exact nature of the mechanistic link between precipitation composition and stream water DOC is still widely debated in the literature. We hypothesize that soil aggregates are the main source of stream water DOC and that DOC release is greater in organic rich, riparian soils vs. hillslope soils. To test these hypotheses, we collected soils from two main landscape positions (hillslope and riparian zones) from the acid-impacted Sleepers River Research Watershed in northeastern Vermont. We performed aqueous soil extracts with solutions of different ionic strength (IS) and composition to simulate changes in soil solution. We monitored dynamic changes in soil particle size, aggregate architecture and composition, leachate DOC concentrations, dissolved organic matter (DOM) characteristics by fluorescence spectroscopy and trends in bioavailability. In low IS solutions, extractable DOC concentrations were significantly higher, particle size (by laser diffraction) was significantly smaller and organic material was separated from mineral particles in scanning electron microscope observations. Furthermore, higher DOC concentrations were found in Na+ compared to Ca2+ solutions of the same IS. These effects are attributed to aggregate dispersion due to expanding diffuse double layers in decreased IS solutions and to decreased bridging by divalent cations. Landscape position impacted quality but not quantity of released DOC. Overall, these results indicate that soil aggregates might be one important link between Critical Zone inputs (i.e., precipitation) and exports in streams.