Experimentally induced soil freezing on soil biogeochemical processes across an elevation gradient at Hubbard Brook Experimental Forest

Background/Question/Methods: Anthropogenic release of greenhouse gases has been implicated in global climate change which could result in an increase in the global mean surface temperature of 4.5 °F (2.5°C) by the middle of the century.  Future climatic scenarios suggest that there will be a reduction in the frequency, duration and amount of snowfall in the middle latitudes that could inadvertently cause extensive soil freezing and increase the freeze thaw cycle and water dynamics, thereby severely impacting the biogeochemical cycles in northern ecosystems.  If soil freezing becomes more common with global warming it could become an important regulator of microbial activities, nutrient cycling, loss and retention, surface water acidification, changes in soil atmosphere trace gas fluxes, uptake processes and forest tree species composition in northern forest ecosystems.   

What is the effect of climate induced soil freezing disturbance across an elevation gradient on soil solution chemistry, trace gases, microbial biomass and N transformation processes at Hubbard Brook Experimental Forest (HBEF) in New Hampshire, USA .  Method/ The soil solution chemistry was collected from the humus (Oa horizons) and mineral (Bs horizons) of randomly designated adjacent paired treatment and reference subplots, each 10 m X 10 m, from each of four sites; East Mt. Kineo, West Mt. Kineo, lower valley and upper valley plots to maximize spatial variability. Treatment plots were kept snow free by shoveling in January 2003/2004 and February 2003/2004 while the reference plots were allowed to accumulate snow at the normal rate. 

Results/Conclusions: There is evidence of treatment effect at the Upper Valley and the West Kineo plots.  Soil solution from organic (Oa) horizon responded more than Bs horizon and there was response to soil freezing across the elevation gradient.  The results also indicate a strong correlation between soil freezing, elevation, vegetation type, horizon, season and year with trace gas fluxes, soil solution chemistry, microbial biomass and N transformation processes.

Climate change towards less snow will result in a shorter duration of snow on the ground that will increase the frequency and duration of soil freezing in northern hardwood forests that will have implications for changes in soil biogeochemical processes.