MSB-ECA: A Lengthening Vernal Window: How Vernal Asynchronies in Energy, Water, and Carbon Fluxes Impact Ecosystem Function

点击翻译按钮获取中文摘要

The vernal window is the transitional period between winter and spring in the northeastern US, when air temperatures warm above freezing, snow melt begins, and forest canopies fully leaf out. The sequential order and timing of physical changes during this window plays a key role in the healthy functioning of seasonally snow-covered ecosystems. The vernal window is shorter following cold, snowy winters but lengthens when winters are warmer and snow packs are shallow or melt multiple times through the winter. When the vernal window gets longer, it can lead to a mismatch in the timing of key ecosystems processes. For example, earlier snowmelt in the spring can flush nutrients from soils before trees emerge from dormancy, preventing trees from accessing those vital nutrients during early spring growth. The vernal window is expected to lengthen given documented warming trends in winter climate, and, under higher emission scenarios may be eliminated altogether in more southerly locations. This study will integrate observations of snow, streamflow, and forest health to document historical changes in the length of the vernal window and use simulations to project future changes in the vernal window. Results will be use to assess the impact on key energy, water, and carbon transitions on ecosystem function, using the northeastern United States forests as a testbed. In collaboration with a local high school classroom, the investigators will develop a low-cost instrumentation suite constructed by students through an inquiry-based lab course that will allow students to track changes in the vernal window in their school yards. A Next Generation Science Standard compliant curriculum with units on energy balance, the carbon cycle, and hydrology will accompany the instrument kit, laying the groundwork for outdoor classroom inquiry on the environment. Previous studies have demonstrated the importance of winter coldness or snowpack as drivers of spring onset, however, it remains unclear how antecedent winter temperature and snowpack properties interact to influence the timing and duration of the vernal window. In addition, previous work has not investigated explicitly how biogeochemical asynchronies that result from longer lags between transitions in the longer vernal window can impact ecosystem function, which is essential for understanding the impact of environmental change. Rapid changes in winter conditions could lead to vernal asynchronies that have strong potential to alter energy, water, and carbon balances. The most extreme case is a shift into a snow-free regime in which the vernal window ceases to exist and is replaced by a prolonged period of increased net radiation into terrestrial and aquatic ecosystems between senescence and leaf out that may fundamentally alter ecosystem function. The work proposed here brings together large existing datasets and process-based models that will be used to investigate explicitly 1) the relative importance of winter coldness and snowpack in altering the vernal window; 2) how longer vernal lags and windows impact ecosystem energy, water, and carbon balance; and 3) how future winter coldness and snowpack characteristics might lead to additional changes in the vernal window. The outcome of this process will be a regional, 30-year historical analysis of changes to energy, carbon, and water balances during the vernal window. Insight gained from this historical analysis will provide the ability to project future changes in not only vernal window length, but also the impact of changing energy, carbon, and water balances during the vernal window on ecosystem function.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.