EPS Colloquium – Charles Harvey, MIT
The Necromass of Borneo
Now more than ever we need to understand how peatlands are formed, how they thrive, and how they can be maintained to control CO2 emissions. I will describe results from a unique field program in Borneo designed to study the coupled ecological and hydrological processes that operate in tropical peatlands. We show how tropical peatlands exist because of a positive feedback between peat accumulation and water table rise. Organic material from tropical rain forests accumulates over millennia in gently-curved domes of peat, tens of kilometers across, that store hundreds of gigatons of organic carbon. But now, newly-constructed networks of drainage canals have broken this feedback, exposing peat to fire and microbial oxidation and releasing huge fluxes of CO2 from peatlands back to the atmosphere. I will describe how the dynamic morphology and carbon fluxes of peatlands can be understood by an elegant, and relatively simple, mathematical formulation of the strong coupling between hydrologic and ecological processes. This mathematical framework is applied to data from one of the last undisturbed peat forests in Southeast Asia. We combine hydrologic, carbon-flux, radiocarbon, and LIDAR data with model simulations to show how peat ecosystem approach a steady-state where: (1) Water table dynamics are uniform across the peat — the water table response to rainstorms is always the same everywhere; (2) The curvature of the land surface is described by a single parameter, a spatially-uniform Laplacian value, that can be predicted from rainfall statistics; (3) Uptake and loss of carbon is balanced over decadal time-scales. Finally, I will describe how this framework enables accurate predictions and management of carbon fluxes and how tropical peatlands have three advantages over most ecosystems for deploying “nature-based solutions” to carbon emissions: (1) Tropical peatlands are concentrated stores and fluxes of carbon; (2) The flux of carbon out of, or into, peat domes can be reliably controlled by “adjusting just one knob”, the depth to the water table and; (3) Peatland carbon stores and emissions are relatively easy to verify by mapping surface elevation. Shifts in the surface of the peat correspond directly to carbon losses and gains because peat is composed of almost entirely or organic carbon.
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Charles Harvey studies hydrogeology, biogeochemistry, and ecology. His group has built field programs in Bangladesh, Borneo, and Cape Cod. They combine data from these sites with novel computational approaches to better understand: Arsenic contamination of well water, a health crisis that threatens millions; Carbon emission from tropical peatlands and; The interaction of fresh water and seawater in coastal aquifers. He has published widely on the physics and chemistry of reactive transport in the subsurface and on geologic carbon sequestration. Professor Harvey has a BA in mathematics from Oberlin College and an MS and PhD in Earth Science from Stanford University. He has worked for the US Geological Survey, was a faculty member at Harvard, and is now a Professor of Environmental Engineering at MIT. He is a fellow of both the American Geophysical Union and the Geologic Society of America and has received the M. King Hubbert Award for contributions to hydrogeology, the Abdulaziz International Prize for Water, and the Meinzer Award for advancing the science of hydrology.