Detection of dissolved pyrogenic carbon export following the Southern California fires of 2017

2017年12月托马斯大火（加利福尼亚州圣巴巴拉县）中燃烧的流域的溪流样本将在火灾后的第一场降雨期间收集，这可能发生在2018年1月至3月。将在这些样品中测量总有机碳和热原碳（即来自燃烧的生物质），并与火灾前这些溪流中的水以及未受火灾影响的邻近流域的溪流中的这些成分的数量进行比较。这些测量的目的是确定火对海洋中溶解有机物的供应和组成的影响。特别是，研究者希望知道溶解的热原碳是否会出口到海洋，因为这是一个有争议的科学课题。如果溶解的热原碳像最近研究表明的那样丰富和流动，它可能对海洋化学、长期碳循环以及相关的气候变化和污染物运输产生强烈影响。另一方面，如果在排放这些被烧毁的流域的小溪中没有检测到比未被烧毁的流域更多的热原C，生物地球化学家将不得不质疑目前用作火灾产生的有机物质标记的方法。该项目的另一个重要影响将是为研究生提供机会，在他的论文中增加一个关于溶解热原碳的实地研究部分。虽然近年来对热原固体性质的了解有所增加，但对热原溶解有机物的性质和循环的研究相对较少。热原溶解有机碳（pyDOC）分析最常用的方法是将凝聚的芳香族成分氧化成更小的、可量化的单体（即苯聚羧酸或BPCAs）。利用这种方法，已经提出pyDOC代表全球河流DOC的恒定比例（~10% pyDOC/DOC）。这个结论是有问题的，因为人们会认为这个比率会随着区域气候和燃烧制度而变化。可能所有这些先前的测量都是在相当大的河流中进行的，即大流域，所以火灾的影响被生物量增长、降水等其他变化所掩盖。此外，pyC可能会不断地从过去火灾中产生的木炭中释放出来。2017年12月的托马斯火灾为探测和表征从陆地到海洋系统的pyC出口提供了理想的场景。圣巴巴拉海峡沿岸有几条短流小溪，它们的小流域完全位于被烧毁的区域内，而在几个毗邻的流域中，类似的小溪由于灭火而在过去60年里没有发生过火灾。调查人员还可以获得储存在这些小溪里的水样，这些水样是在托马斯大火之前采集的。可能没有比这更好的方案了，既可以发现支持或反对向海洋大量出口热原C的主张的无可争辩的证据，也可以量化这种出口流量（如果存在的话）。

Water from stream samples draining watersheds burned in the Thomas fire of December 2017 (Santa Barbara County, California) will be collected during the first rains following the fire, which are likely to occur in January-March, 2018. Total organic carbon and pyrogenic carbon (i.e. derived from burned biomass) will be measured in these samples and compared with quantities of these components in water of these streams prior to the fire, and in streams of adjoining watersheds not affected by the fire. The objective of these measurements is to determine the influence of fire on the supply and composition of dissolved organic matter to the ocean. In particular, the investigator wishes to know whether dissolved pyrogenic carbon will be exported to the ocean as this is a controversial scientific subject. If dissolved pyrogenic C is as abundant and mobile as recent studies suggest, it may have a strong impact on marine chemistry, long-term C cycling and associated climate changes and pollutant transport. On the other hand, if pyrogenic C is not detected in the creeks draining these burned watershed in amounts greater than that of the unburned watersheds, biogeochemists will have to question the methods currently used as markers for fire-produced organic matter. Another important impact of the project will be to provide the opportunity for a graduate student to add a field component to his dissertation research on dissolved pyrogenic carbon.While knowledge of the properties of pyrogenic solids has increased in recent years, there has been relatively little study of the properties and cycling of pyrogenic dissolved organic matter. The method most commonly used for pyrogenic dissolved organic carbon (pyDOC) analysis involves the oxidation of condensed aromatic constituents into smaller, quantifiable monomers (i.e., benzenepolycarboxylic acids or BPCAs). Using this method, it has been suggested that pyDOC represents a constant proportion of riverine DOC globally (~10% pyDOC/DOC). This conclusion is problematic since one would expect this ratio to vary with regional climate and burning regimes. It may be that all these previous measurements were made in fairly large rivers, i.e. large watersheds, so the effects of fire have been hidden by other variations in biomass growth, precipitation etc. Also, pyC may be continually released from charcoals made during past fires. The Thomas fire of December 2017 provides an ideal scenario for detecting and characterizing pyC export from terrestrial to marine systems. There are several short-run creeks draining coastal catchments along the Santa Barbara Channel that have small watershed completely within the burned area, and similar creeks in several adjoining watershed that saw no fire for the past 60 years due to fire suppression. The investigator also has access to water samples that have been in storage from these creeks taken prior to the Thomas fire. There is probably no better scenario for detecting indisputable evidence for, or against, the claim of significant export of pyrogenic C to the ocean, as well as quantifying that export flux if it exists.