Soil Carbon Stocks and Greenhouse Gas Fluxes from Unrestored Sierra Nevada Meadow Ecosystems.

High elevation Sierra Nevada meadows provide many ecosystem services such as water supply, water quality, and carbon sequestration. Sierra meadows have been disturbed since Euro-American settlement, but recently meadow restoration efforts have begun. Among the many benefits of restoration could be the ability to sequester carbon, thereby providing a mechanism to pay for the restoration using, e.g., California’s cap and trade legislation. Much needs to be learned before such a marketplace is possible: How much carbon is in unrestored meadows, and what are the rates of greenhouse gas fluxes from these meadows? What is the target soil moisture for meadow restoration to begin to sequester carbon? Could restoration create methanogenic conditions that would offset C sequestration? To address these questions, we measured soil carbon stocks in three unrestored Sierra Nevada meadows to a depth of one meter, we measured the magnitude and direction of in situ soil carbon dioxide, methane, and nitrous oxide fluxes using vented static chambers, and we performed a laboratory incubation at different soil water contents to identify optimal conditions for soil carbon sequestration. Our results suggest that substantial amounts of carbon persist in unrestored meadow soil. However, this carbon is vulnerable to decay because these meadow soils also respire substantial amounts of carbon dioxide. For most of the year, unrestored meadows are net sinks of methane and a small source of nitrous oxide. Both field and laboratory results indicate that standing water is necessary for meadow soil to be a net sink of carbon dioxide, but in some cases, emissions of methane and nitrous oxide may be a concern for net greenhouse gas emissions. As restoration ecologists increasingly recognize the ecosystem services and potential financial opportunities of soil carbon sequestration, these data provide important baseline information that constrain, parameterize, and elucidate the possible response of soils to meadow restoration.