Carbon is the main building block of all vegetation, as well as the organic component of soils. In order to predict the effects of wildfires on forest carbon storage in a future where more fires are expected to occur, a better understanding of the cycling of carbon is therefore critical. This project focuses on pyrogenic, or black carbon and its related fluxes, a component that has been largely ignored in earlier studies. During fire a fraction of the burned carbon, perhaps up to ten percent of the total, is converted to black carbon and deposited in the soil, where it may runoff in water or remain stored. In many fire-prone ecosystems, black carbon comprises more than 20 percent of soil organic matter. The High Park Fire burned more than 35,000 hectares in June 2012 along the Cache la Poudre River in Northern Colorado and, in the process, created a unique opportunity to conduct a full initial accounting of black carbon dynamics, from production to deposition, storage, and runoff.
This project will determine the rate of production of black carbon from the High Park Fire, its rate of loss in erosion compared to its accumulation deeper in soil, its export by water runoff through an intensive water monitoring effort, and deposition along river banks and in stream bed sediments. Stored samples of sediments and water from before and after the fire will be used along with new samples taken over the following year. State of the art methods will be used to accurately quantify black carbon in all soil, sediment and water samples. This will provide valuable measurements in support of a more mechanistic understanding and modeling of black carbon dynamics in mountain ecosystems increasingly prone to fires.
After the many fires of 2012, the general public is more than ever interested in their causes and consequences. An open panel on fires, pyrogenic carbon, and their impacts on water resources and climate change will be organized locally. Additionally, the project will develop an inquiry project aimed at engaging secondary school students in Colorado Front Range communities and rural eastern Colorado, which includes a large Hispanic population. A lesson on black carbon will be framed as a forensic detective mystery to determine where and when a fire occurred. Students will analyze samples to solve the mystery and lead into discussions on the causes and consequences of wildfires. Effectiveness of outreach will be assessed using pre- and post-tests administered by experts at Colorado State University.
During fire, a fraction of the carbon (C) in the burned biomass, estimated to range from 0.12 to 9.5%, is converted to pyrogenic or black C (BC) and deposited in the soil, where it may runoff or remain in the system for up to centuries. In many fire-prone ecosystems, BC comprises more than 20% of the soil organic carbon, however, we know very little about the amounts and controls of pools and fluxes of BC, in particular at the watershed scale. In June of 2012, the High Park Fire burned an area of more than 35,000 ha along the Cache la Poudre River in Northern Colorado, USA. This extreme event offered us the opportunity to conduct a full initial accounting of BC in soils and sediments, and runoff in waters at the watershed scale. We found that the majority of the BC deposited immediately following the fire remained on the soil surface (litter layer) and was equal in moderate and highly burned sites. Surprisingly there was no difference in BC stocks, between steep and flat sites. At the time of sampling, none of the BC deposited on the land surface post-fire had been incorporated into the mineral soil. Our BC chemical marker analysis indicated there was significantly older BC along the soil profile. Total BC soil stocks were relatively low compared to other fire-prone grassland and boreal forest systems, indicating most of the BC produced in this system was likely transported off site through erosion events. In fact the BC content of sediment samples, collected within the watershed months after the fire was similar to that we measured in the litter layer of burned sites, in the aftermath of the fire. We found evidence for some of this mobile BC to be exported in particulate and dissolved form off the watershed, but also for some to be deposited on the river banks, as well as in depositional areas - identifiable as black layers of soil. These depositional areas have recently been recognized as significant BC pools in the BC biogeochemical cycles. Beside thesenovel and important results which we presented at conferences and published in a peer reviewed journal, data from this study were leveraged to obtain further support to broaden the black carbon research program at Colorado State University (CSU), also through international collaborations. Thanks to this project we developed a BC chemical marker (Benzene Polycarboxylic Acids) analytical method at the EcoCore Analytical Service facility at CSU. The facility now offers the BPCA analyses to any researcher world-wide as a service. A major broader impact outcome of this project is the design and realization of Soil Carbon educational kits, used to deepen the passion for and level of understanding of fire impacts on soils of K-12 students and teachers.
