Dynamics of dissolved organic matter in headwaters: comparison of headwater streams with contrasting DOM and nutrient composition
Dynamics of dissolved organic matter in headwaters: comparison of headwater streams with contrasting DOM and nutrient composition
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DOI：
10.1007/s00027-020-0704-6
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发表时间：
2020-02-24
期刊：
影响因子：
2.4
通讯作者：
Evans, Chris D.
中科院分区：
文献类型：
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作者：
Fovet, Ophelie;Cooper, David M.;Evans, Chris D.
淡水中的溶解有机物(DOM)被认为是全球碳收支中一个重要而活跃的组成部分。从陆地生态系统出口的DOM在向下游运输时，可能会因化学和生物反应而在成分和功能上发生变化。影响源头溪流中DOM的过程仍然不确定，但潜在地高度可变，这取决于DOM的组成和作为土壤、土地利用和人类压力的函数的养分可获得性。为了研究DOM活性的变异性，我们从两个不同的水源流域采集了水样，这两个流域被认为是DOM出口的功能性“终端成员”：一个富含芳香DOM但无机养分含量低的流域(泥炭地)，以及另一个(附近)DOM芳香较少、养分负荷较高的集水区(农业草地)。在受控的实验室条件下，我们评估了光照、水生生物的存在或不存在以及营养物质的增加对这些样品中DOM数量和质量的短期变化的影响。对于泥炭溪流，暴露在阳光下(含紫外线)导致非生物DOM的净去除，而在农业溪流中，它导致生物DOM的净产生。营养物质的添加加速了两条溪流中DOM的产生。我们的结论是，河流中DOM数量和质量的变化代表了多个消费和生产过程的净影响，其相对重要性受到依赖于源的DOM组成和环境因素的强烈影响，如无机养分含量和阳光照射。我们的发现表明，源头溪流可能是碳和营养物质的更活跃的加工者，而不是迄今所推测的。
Dissolved organic matter (DOM) in freshwaters is recognised as a significant and active component of the global carbon budget. DOM exported from terrestrial ecosystems may be compositionally and functionally altered by chemical and biological reactions as it is transported downstream. The processes affecting DOM in headwater streams remain uncertain but are potentially highly variable depending on DOM composition and nutrient availability as a function of soils, land-use, and human pressures. To investigate variability of DOM reactivity we took water samples from two contrasting headwater catchments, considered functional 'end-members' for DOM export: one rich in aromatic DOM and low in inorganic nutrients (peatland), and another (nearby) catchment characterized by less aromatic DOM and high nutrient loadings (agricultural grassland). Under controlled laboratory conditions, we evaluated the effects of light, presence/absence of aquatic biota and nutrient enrichment on short-term changes in DOM quantity and quality in these samples. For the peat stream, exposure to sunlight (with UV) resulted in net abiotic DOM removal, whereas in the agricultural stream it led to net biological DOM production. Nutrient addition accelerated DOM production in both streams. We conclude that in-stream changes in DOM quantity and quality represent the net effect of multiple consumption and production processes whose relative importance is strongly influenced by source-dependent DOM composition and environmental factors such as inorganic nutrient content and sunlight exposure. Our findings suggest that headwater streams may be more active processors of carbon and nutrients than presumed hitherto.