1. Winter is considered the dormant season due to low temperatures, however, in soil there
is more activity during winter than previously thought (1). While deciduous forest trees are
inactive during winter, insulating snowpack keeps temperatures favorable for a wide range of
belowground processes. Lack of plant activity during winter makes belowground processes
especially important for retaining essential nutrients, particularly nitrogen, in the litter layer (2),
and maintaining forest productivity and water quality. The litter layer is an important reservoir of
essential nutrients, which allows gradual recycling of nutrients into plant available pools in the
form of dissolved and particulate organic matter. Stream nitrate concentrations have been shown
to increase following low snow years, suggesting soil freezing was responsible (3). Snow
manipulation experiments verified soil freezing as the cause of increased leaching of nitrate and
dissolved organic matter (4). Uncertainties remain regarding soil frost effects on the stability of
nutrient retention in the litter layer, because previous studies could not distinguish the proportion
of C and N lost from “young” litter and “old” soil organic matter (SOM). Moreover, those
studies do not represent long-term differences in climate, as they cannot induce a gradual change
in soil frost associated with winter climate change.
I propose to study snowpack effects in different climates by using an elevational gradient
in snowpack. I will examine questions of source organic matter and N leaching, raised in
previous studies by tracing 13
C and 15
N from isotopically-labeled leaf litter. I hypothesize that
reduced snowpack will accelerate recycling and retention of C and N in the litter layer. I predict
that sites with shallow snowpack and deeper soil frost will leach more litter-derived organic
matter and N, compared to sites with deeper snowpack and less soil frost.
Movement of 13
C and 15
N through the soil profile via soil solution will be collected from
six sites located along a snowpack gradient. Zero-tension soil lysimeters were installed below the
organic horizon in May 2011 to collect soil solution, and will be sampled once a month for two
years. Soil solution subsamples will be sent for isotopic analysis of 13
C and 15
N in particulate and
dissolved organic C and N, and dissolved inorganic N to the stable isotope facilities at the
University of California at Davis and Boston University.
Results of increased leaching of litter-derived C and N, would suggest that deeper soil
frost arising from low snowpack, impairs C and N retention in fresh litter and could have
subsequent effects on short-term nutrient pools regulating forest productivity and soil C storage.
Alternatively, results of no difference in litter-derived C and N retention, would suggest that
losses are primarily from SOM, affecting long-term nutrient pools important for productivity and
soil C storage. This study is one complementary part of a larger project examining the fates and
transformations of elements in soil at the Hubbard Brook Experimental Forest in NH. These
results will help to enact climate change policies and better natural resource management
strategies.

2. Supplies #items/amount Cost
Boston University isotopic analyses
of:
- 13
C-POC + 15N-PON*
- 15
N-DON
- 15
N-DIN
University of California at Davis
isotopic analysis of 13
C-DOC
160 samples
180 samples
180 samples
204 samples
$8.00 per sample = $960
$6.00 per sample = $1,080
$6.00 per sample = $1,080
$16.00 per sample = $3,264
Total cost
*Requesting from Sigma Xi
$6,384
$960
Budget justification
I am applying for non-Sigma Xi funding for 15
N-DON and 15
N-DIN, and 13
C-DOC analyses. My
lab does not have the necessary instruments to conduct these analyses. Although all isotopic
analyses are crucial for my project, I am only requesting funds for the isotopic analyses of 13
C-
POC and 15
N-PON, which would provide me with the most complete dataset on litter-derived
particulate organic matter.
References
1. Campbell, J. L., Mitchell, M. J., Groffman, P. M. , Christenson, L. M., Hardy, J. P.
2005.Winter in northeastern North America: a critical period for ecological processes. Front
Ecol Environ. 3: 314-322.
2. Fahey, T. J., Yavitt, J. B., Sherman, R. E., Groffman, P. M., Fisk, M. C., Maerz, J. C. 2011.
Transport of carbon and nitrogen between litter and soil organic matter in a northern hardwood
forest. Ecosystems. 14: 326-340.
3. Groffman, P. M., Hardy, J. P., Fashu-Kanu, S., Driscoll, C. T., Cleavitt, N. L., Fahey, T. J.,
Fisk, M. C. 2011. Snow depth, soil freezing and nitrogen cycling in a northern hardwood forest
landscape. Biogeochemistry. 102: 223-238.
4. Christenson, L. M., Mitchell, M. J., Groffman, P. M., Lovett, G. M. 2010. Winter climate
change implications for decomposition in northeastern forests: comparisons of sugar maple litter
with herbivore fecal inputs. Global Change Biology. 16: 2589-2601.