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)烧毁的分水岭的溪水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1-3月。将在这些样本中测量总有机碳和热解碳(即从燃烧的生物质中提取)，并将其与火灾前这些溪流的水中以及不受火灾影响的毗邻流域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。调查员特别想知道溶解的热解碳是否会出口到海洋，因为这是一个有争议的科学问题。如果溶解的热源碳像最近的研究表明的那样丰富和可移动，它可能会对海洋化学、长期的碳循环以及相关的气候变化和污染物传输产生强烈的影响。另一方面，如果在排放这些燃烧的分水岭的小溪中没有检测到热源C的数量大于未燃烧的分水岭的量，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，在他的学位论文中增加关于溶解热源碳的研究。尽管近年来对热源固体性质的了解有所增加，但对热源溶解有机物的性质和循环的研究相对较少。热解溶解有机碳(PYDOC)分析最常用的方法是将稠合的芳香族化合物氧化成更小的、可定量的单体(即苯多羧酸或BPCA)。利用该方法可以得出，在全球范围内，河流DOC占总DOC的比例是恒定的(约为10%)。这一结论是有问题的，因为人们预计这一比率会随着地区气候和燃烧制度的不同而变化。可能所有这些以前的测量都是在相当大的河流，即大流域进行的，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，过去火灾中产生的木炭可能会不断释放出热解碳。2017年12月的托马斯大火为探测和表征从陆地到海洋系统的热带雨林出口提供了一个理想的场景。圣巴巴拉海峡沿线有几条排干沿海集水区的短期小溪，完全在烧毁区域内有一个小流域，以及几个相邻分水岭的类似小溪，由于灭火，这些小溪在过去60年里没有起火。调查人员还可以获取托马斯火灾前储存在这些小溪中的水样。可能没有更好的方案来检测支持或反对大量向海洋出口热源C的说法的无可争辩的证据，以及量化出口通量(如果存在)。

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.