Environmental Research

Atmospheric CH4 is the second most significant driver of climate change behind CO2 as anthropogenic sources have contributed to a higher atmospheric CH4 concentration today than anytime within the last 800,000 years (Calvin et al., 2023). Aquatic ecosystems contribute approximately half of all global methane (CH4) emissions with reservoirs producing 9-28 Tg yr-1 (D’Ambrosio & Harrison, 2022; Rosentreter et al., 2021). Predictions of global CH4 emissions from reservoirs are highly uncertain, however, due to the wide spatial and temporal variations in CH4 flux rates and the highly variable role of ebullition (bubbling) versus diffusion in CH4 transport from the sediment to the water surface.

This project, which began in 2020, seeks to quantify CH4 flux rates from Uvas Reservoir, a monomictic, mesotrophic reservoir managed by the Santa Clara Valley Water District in Morgan Hill, California. Total CH4 flux rates are measured semi-continuously using the eddy-covariance method in conjunction with other local meteorological and water quality parameters to determine environmental drivers of CH4 emissions. Post-collection data analyses are used to partition diffusive and ebullitive flux rates to give further insight to the precise mechanisms that drive CH4 fluxes on a sub-daily timescale and improve emissions predictions.

Comprised of some of the tallest, longest-living, and most biomass-dense trees per area on Earth, the California coastal redwood forests are estimated to be the most efficient major land resource area for carbon sequestration in California (Busing & Fujimori, 2005; Potter 2010). However, present estimates of net ecosystem exchange in this environment are limited and do not quantify variations at the stand scale where age, terrain, and management strategies can impact carbon exchange  (Brown, 2013; Jones & O’hara, 2012; Potter, 2012; Sillett et al., 2010).

To understand the influence of stand-scale characteristics and complex terrain on carbon dioxide fluxes above, below, and within coastal redwood forest canopies, two eddy-covariance flux towers were constructed rising above young and intermediate growth stands at Jackson Demonstration State Forest in 2025. Horizontal and vertical CO2, water vapor, and temperature profiling systems are mounted with anemometers to determine the contribution of subcanopy advection and storage to net ecosystem exchange in addition to vertical turbulent transport. This project is a collaboration between the California Department of Forestry and Fire Protection, Lawrence Berkeley National Laboratory, University of California, Davis, California Air Resources Board, and California Natural Resources Agency.

Atmospheric boundary layer (ABL) turbulence studies were conducted using a doppler LiDAR (Light Detection and Ranging) sensor to determine the impact of urban features on atmospheric turbulence in collaboration with the California Air Resources Board (Aug. 2024) and in Blodgett Forest (Nov. 2023) to investigate the influence of pile burns on local convective cells, atmospheric scalar fluxes, and ABL height with collaborators from UC Irvine. Experimental setup and data collection were managed by UC Davis Oldroyd Lab members, Corrin Clemons and Matt Miksch, while data processing has been overseen by Miksch and members of the Banjeree Lab at UC Irvine.