The transport and accumulation of pyrogenic black carbon in recently burned watersheds and implications for water quality

自20世纪50年代以来，森林火灾的强度和频率有所增加，并且由于过去的火灾管理策略、气候变化和土地利用的转变，预计将继续增加。黑碳（BC）以烟灰和炭的形式，由有机物的不完全燃烧产生，并通过野火后的降雨和洪水事件在下游山谷和水道中运输和重新沉积。野火产生的黑碳对水质既有负面影响，也有积极影响。例如，在短期内，它可能污染饮用水供应，并产生对水生生物有害的缺氧条件。但是，在景观上产生的BC沉积物可能起到碳汇的作用，并可能通过吸附来隔离大量的污染物和重金属。该项目将研究新墨西哥州北部最近两次野火的影响，目的是了解野火后流域BC的运输、积累和停留时间，以及这些BC沉积物的环境意义。黑碳将在烧伤地区、烧伤下游和未受野火影响地区的土壤中进行测量。将在预计会发生动员的两个夏季季风季节前后采集样本，以便了解运输和积累速率。实验室分析将测量土壤样品中几种重金属和燃烧副产品污染物的含量，以及土壤中BC成分的百分比。进一步的分析将量化土壤中BC吸收和隔离这些污染物的最大能力。考虑黑碳的重要性至少有三个原因：全球碳循环、污染物封存和土壤肥力。BC传统上被认为是一种化学稳定的碳形式，有人建议将BC添加到土壤中作为一种改良剂可以作为碳汇。然而，最近的研究发现，BC从土壤中去除的速度比以前认为的要快。研究人员发现大量的BC溶解在河水中，这可能意味着通过土壤渗透的水溶解了一些BC。含BC的沉积物的侵蚀和运移是BC从土壤中移除的另一种方式，但这一机制受到的关注较少。这项工作将有助于量化这一知之甚少的碳循环组成部分。预计这些发现在利用易发火灾的森林流域作为饮用水来源的地区尤其相关，这是美国西南部大部分地区的情况。作为城市水源的流域土壤中黑碳的存在可能为污染风险提供额外的缓冲。研究结果还将协助管理人员制定火灾后的恢复计划，并可能对化学品泄漏后的生态风险评估有用。这项工作将支持培训两名文学硕士水平的水文学家，并为新墨西哥矿业与技术研究所的一名本科生提供研究经验，这是一所西班牙裔的服务机构。

The intensity and frequency of forest fires have increased since the 1950s and are predicted to continue to increase as a result of past fire management strategies, climate change, and shifts in land use. Black carbon (BC), in the form of soot and char, is generated by incomplete combustion of organic matter and is transported and re-deposited throughout downstream valleys and waterways by post-wildfire rainfall and flood events. Black carbon from wildfires has the potential for both negative and positive impacts on water quality. In the short term, for example, it may foul drinking water supplies and generate of anoxic conditions that are harmful to aquatic life. But the BC deposits produced on the landscape may act as carbon sinks and may sequester significant quantities of contaminants and heavy metals through sorption. This project will study the impacts of two recent wildfires in northern New Mexico with the goal of understanding the transport, accumulation, and residence times of BC in post-wildfire watersheds, as well as the environmental significance of these BC deposits. Black carbon will be measured in soils within burned areas, downstream of burns, and in areas unaffected by wildfires. Samples will be taken before and after two summer monsoon seasons, when mobilization is expected to occur, in order to understand transport and accumulation rates. Laboratory analysis will measure the amount of several heavy metals and burn-byproduct contaminants contained within the soil samples, and what percentage is held within the BC component of the soils. Further analysis will quantify the maximum capacity of the BC in the soils to sorb out and sequester these contaminants. Black carbon is important to consider for at least three reasons: global carbon cycling, contaminant sequestration, and soil fertility. BC has traditionally been viewed as a chemically stable form of carbon, with suggestions that the addition of BC to soils as an amendment could serve as a carbon sink. Recent work, however, has found that BC is removed from the soil more rapidly than previously thought. Researchers have found significant quantities of BC dissolved in river water, which may mean that water percolating through the soil dissolves out some BC. Erosion and transport of BC-containing sediment is an additional way by which BC may be removed from soils, and this mechanism has received much less attention. This work will contribute to quantification of this poorly understood component of the carbon cycle. The findings are anticipated to be particularly relevant in areas that utilize fire-prone forest watersheds as a source of drinking water, which is the case for most of the southwestern US. The presence of black carbon in the soils of watersheds that are municipal water sources may provide an additional buffer to contamination risks. The results will also assist managers in developing post-fire recovery plans and may also be useful for ecological risk assessment following chemical spills. This work will support the training of two hydrologists at the MS level and provide a research experience for one undergraduate from New Mexico Institute of Mining and Technology, a Hispanic serving institution.