Summer Precipitation Patterns Alter Soil Moisture and Carbon Dynamics in a High Elevation Meadow

Abstract:

High elevation meadow ecosystems in the Sierra Nevada Mountains and beyond are expected to experience shifts in precipitation patterns over the coming century. While the majority of precipitation falls in the form of rain and snow during the winter months, smaller discrete precipitation events occur during the summer months. These events play an important role in regulating soil moisture dynamics, and biogeochemical cycling of essential elements, including carbon and nitrogen. Preliminary data from a large subalpine meadow in Yosemite National Park, shows a marked decrease in the number of June, July and August pulse events over the last 30 years and a shift toward more smaller events earlier in June and infrequent larger events in July and August. In order to better understand the overall impact these changes have on carbon cycling in meadow ecosystems, detailed studies of current ecosystem functioning is critical. The overall objective of this study is to clarify the spatial and temporal distribution of soil moisture and carbon dioxide fluxes in response to precipitation pulses extending from spring melt through late summer in dry vs. wet meadow sites at a high elevation ecosystem. We found that: (1) Vertical and horizontal heterogeneity in soil moisture is a function of the timing, amount and duration of summer convective precipitation pulse events; (2) The effect of summer convective precipitation pulse events on soil respiration is most heavily influenced by timing between events rather than the magnitude of each event, with more pronounced effects in dry rather than wet meadow locations.