|Peter M. Groffman
Cary Institute of Ecosystem Studies
2801 Sharon Turnpike
Millbrook, NY 12545 USA
phone: (845) 677-7600, ext. 128
fax: (845) 677-5976
THERE IS considerable uncertainty about how changing winter climate will alter patterns of snow depth, soil freezing and the processing of carbon (C) and nitrogen (N) in ecosystems. Current research is using a landscape-scale approach to evaluate three aspects of the effects of changes in snow depth on soil freezing, the processing of C, and N retention in the northern hardwood forest. First, we are addressing uncertainty about the occurrence of colder soils in a warmer world, and whether this pattern will decrease N retention in the northern hardwood forest. Uncertainty about the extent and effects of soil freezing in a warmer world is rooted in limitations in our understanding of where two "tipping points" occur across a forest landscape experiencing climate change; where snowpacks are too shallow to insulate the soil, and where air temperatures are too warm to freeze the soil. This uncertainty is being addressed by measuring and modeling snow depth, and soil climate across the entire ~3000 ha Hubbard Brook Experimental Forest (HBEF), which encompasses the range of climate variability that has been predicted for the northeastern U.S. over the next 50 – 100 years. Spatially explicit models of snowpack and soil climate were used to locate 20 experimental field sites that experience a broad range of long-term snowpack regimes. Measurements of soil temperature, moisture and frost, soil solution chemistry and transport and microbial biomass and activity are being made at these sites to explore critical uncertainties surrounding soil freezing events and their effects on C processing and N retention.
Second, the research is addressing how winter climate change affects microbial and soil invertebrate processes and resultant changes in C flow during winter. This work is driven by the hypothesis that C flow is the key integrative regulator of winter microbial activity and that winter climate change effects on this activity are mediated through effects on C flow in dissolved organic carbon (DOC) and particulate organic carbon (POC) derived from the partial decomposition of litter and soil organic matter. To test this hypothesis, we are tracing movement of
Third, the proposed research is addressing if soil freezing alters hydrologic controls of ecosystem N processing at snowmelt and subsequent watershed N export. Previous studies suggest that N retention during the late winter/snowmelt period is generally high and a critical controller of annual export from northern hardwood forest ecosystems. This retention may involve an interaction between immediate abiotic retention during winter followed by remobilization and biotic cycling and retention during both dormant and growing seasons. This mechanism is being tested by adding 15NO3- to the snowpack and tracing its movement into microbial biomass, roots and abiotic uptake at the six intensive study sites. A major challenge in soil freezing/winter climate change research has been the inability to reconcile strong effects observed at the plot scale that are not consistently observed at the whole-watershed scale. This may be caused by changes in hydrologic flowpaths caused by soil freezing that decrease shallow subsurface flow and increase retention of N as it moves across the landscape. This hypothesis is being tested by analyzing N export and solutes that serve as natural tracers of hydrologic flowpaths on small watersheds that differ in winter climate/soil freezing ( north versus south facing watersheds at HBEF).
The project includes education and policy activities that explore the effects of winter climate change in the Northeast U.S. on recreation, timber harvesting, biomass energy production, and other ecosystem services. We are connecting ecosystem researchers with relevant stakeholders and interest groups, including loggers and foresters, ski-area operators, maple sugar producers, recreational snowmobile users, conservation-oriented NGO's, citizen scientists, and public and private land managers through a "Science Links" program. There are also two pilot educational initiatives: a winter field course for undergraduates and creation of a teaching guide for middle and high school teachers.
Date Prepared: November 2012