Monday, April 27, 2015 at 3:46PM
NEON & INSTAAR
ARC room 620
What happens when it rains? Ecosystem fates of N deposition during experimental rainfall in the Colorado Front Range
Climate is changing in the Colorado Front Range, leading to declines in snowpack below 8200 feet and a greater proportion of total annual precipitation falling as rain. Several decades of research in alpine ecosystems have demonstrated the links among climate, hydrologic response, and the fate of atmospheric nitrogen (N) deposition – another driver of ecosystem change. In this study, I collaborated with colleagues at INSTAAR and the USGS to investigate the fate of N deposition under increasingly important rain events at the rainsnow transition of the Colorado Front Range. We conducted experimental rainfall events labeled with lithium bromide and 15N-nitrate (NO3-) on north- and south-facing hillslope aspects within Boulder Creek CZO’s montane study catchment. During the experiments, we measured subsurface tracer transport and recoveries of 15N species in soils and microbial biomass. We found that hillslope position was a significant determinant of soil 15N-NO3- recoveries, while soil depth and time since rain event were significant determinants of 15N recovery in the microbial pool. Dry conditions during the growing season led to little movement of tracers in soil solution. Overall, microbial uptake and hydrologic transport of N was greater on the north- than the south-facing slopes. Our data point to the importance of soil properties (e.g., presence/absence of organic horizon, and degree of macroporosity) as a control on ecosystem N retention. I will discuss the implications of these findings for the function of mid-elevation ecosystems impacted not only by changing climate and nutrient deposition, but also fire and pine beetle kill.
Free and open to the public.