ABSTRACT

Wildfire suppression is a common forest management practice in the western world. However, land management practices for fire are shifting, and many communities and agencies are planning to prescribe more wildfire in fire-prone landscapes. At the same time, global climate change has increased extreme fire weather days in places like the western United States. From both a global climate change and a more regional land management perspective, fires will become a more commonplace land disturbance, and this expected increase in wildfire extent places even greater importance on bringing science up to speed with the effects of wildfire on watershed processes. Understanding of interacting hydrological and biogeochemical components in pre- and post-fire watersheds at-large remains limited and virtually nonexistent for coastal draining systems. This project will help fill this gap by: (1) leveraging gauged coastal watersheds with existing data that facilitates temporal comparisons of pre- and post-fire water quality and water yields, and (2) using multiple tracers to delineate source contributions from burned and unburned areas of each coastal watershed. Four of the five proposed study watersheds provide drinking water to ~90,000 citizens in Santa Cruz County. This project would build on city and county efforts to better understand the impacts of wildfire on municipal drinking water supply, and results will be shared with existing collaborators and contacts at the City of Santa Cruz, County of Santa Cruz, Bureau of Land Management, and California State Parks. This work will support two early-career female researchers and two students.

Small watersheds (<1000 km2) comprise nearly 1/5 of all watersheds on Earth and the majority of watersheds along the California coastline. While these systems are globally ubiquitous, comprehensive hydrological and biogeochemical data for these small systems is limited, and even less is known about how these coastal systems respond to wildfires. To fill this knowledge gap, investigators propose to examine near-term wildfire impacts on coastal stream water material exports to better understand how fire can alter material sourcing, composition, and concentrations across dynamic flow regimes. They will focus on stream water particulate and dissolved carbon (C) and nitrogen (N) compounds as they are fundamentally important to local food webs and drinking water quality. Specifically, they propose to: (1) leverage paired watersheds with varying biophysical watershed characteristics to better understand differences in water quality responses post-fire, and (2) use multiple lines of evidence (stable isotopes, optical properties, C and N ratios, and direct quantification of pyrogenic C to differentiate contributions from burn affected and unburned regions of each watershed. This study will provide new insight into how coastal stream C and N sources, composition, and exports vary across flows in response to wildfire. This insight is critical to better understanding how wildfire can alter C and N sources, transport, and fate in coastal draining systems.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

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