Wildfire, although a natural and periodic phenomena, has an immediate and sometimes devastating effect on watersheds. The impacts of wildfire can include high rates of overland flow, high sedimentation rates, decreased water quality, and destructive debris flows. Southern California is prone to widespread fires at the urban-wildland interface due to its Mediterranean climate (wet winters, dry summers), prevalent Santa Anna winds during the fall season, and an ever-expanding population which is responsible for igniting many of the observed fires. The Day Fire, which recently occurred north of Los Angeles, consumed nearly 254 square miles of National Forest and designated wilderness areas. Several major drinking water reservoirs for the metropolitan region are located downstream from the Day Fire burn area, presenting an immediate and serious concern for water resource managers. One of these reservoirs, located on the eastern fringe of the burn, is Pyramid Lake, which stores water from the California Aqueduct as well as natural inflows from the Piru Creek watershed. The objective of this proposal is to understand the physical and chemical mechanisms that control nutrient, metal and other contaminant fluxes in post-fire watersheds, with a focus on the Pyramid Lake reservoir system. A SGER grant is critical to this objective as it allows an immediate field campaign focused on the physical and chemical parameters related to likely primary problems. Intellectual Merit. This work addresses fundamental questions on the impacts of fire on metal and nutrient transport and cycling in watershed systems. By enabling coordinated, spatiotemporally dense observations of multiple parameters in terrestrial, aqueous and sediment phases within one watershed system, we will be able to elucidate complex transport relationships in post-fire watersheds. While there has been considerable literature demonstrating the effects of fire on hydrologic processes, we do not fully understand the relationships between sediment flux and nutrient and metal transport in post-fire systems. Ultimately, we plan to use the collected data to develop mechanistic and watershed scale models of nutrients, metals and sediment transport in postfire watershed systems. Broader Impacts. The proposed research represents a unique opportunity to understand a crucial water quality issue, while also synergizing with on-going hydrological and geomorphologic studies to define and address issues fundamental to response and recovery in burned watersheds. Our study will be the first to investigate the potential effects of fire on nutrient and metal transport in a streamreservoir system which is an integral part of the regional water supply in a semi-arid region. Ecosystem and water supply managers will be able to utilize information gathered in this study to develop mitigation and warning strategies for reducing the impacts from increased metal and nutrient fluxes in burned watersheds. This proposal will also contribute to the education of one Ph.D. graduate student at UCLA, as well as undergraduate students at the University of the Pacific and UCLA. UCLA undergraduate students will develop undergraduate research projects (taken as CEE199) involving data collection and analysis, field surveys, and/or modeling studies, and Pacific undergraduate students will incorporate data collection and analysis into Senior Thesis projects.
