UC Merced

High elevation meadow ecosystems play a fundamental role in the storage and movement of water from the snowpack to the streams. The vulnerability of such systems to extreme changes in the depth and duration of snowpack in a given year is unknown. However, due to the coupled nature of the hydrological and biogeochemical cycles in the meadows, it is expected that a change in hydrology will impact biogeochemistry and vice versa. This research investigates the gaps in our knowledge of the coupled hydrology and carbon cycling of meadow soils, and forges new territory in our understanding of the impacts of lowered water tables and desiccation on the hydrologic resiliency of those soils. This knowledge is critical in snowmelt-dominated watersheds, where meadows (both high elevation and montane) serve as natural storage reservoirs that feed both streams and groundwater.

Here I investigate the distinctly different water years of 2011 to 2013 and illustrate how sensitive subalpine meadow systems are to extreme variation in weather. Focused on three main themes of resiliency, thresholds and change in high elevation meadow ecosystems, I found that a) nonlinear responses in ecosystem processes can cause ecosystems to shift from a sink to a source of carbon contributing to local (degradation of ecosystem), regional (loss of ecosystem services) and global effects (feedback to atmosphere), b) winter drought and spring frost events can significantly damage vegetation, reducing the productivity of vegetation, which leads to a decrease in carbon sequestration, c) thresholds in moisture availability can influence the magnitude of carbon loss via soil respiration, d) Longer growing season with little summer precipitation contributed to severe desiccation of meadow soils which caused an irreversible change in the structure of the soil and subsequent loss of porosity and permeability. A new method was also developed to detect a signature of historic dryness in soils.

Findings of this study highlight the need to consider the timing of seasonality in mountain regions on the coupled hydro-biogeochemical dynamics when trying to assess resilience of meadow systems under a changing climate.