Effect of Snow Removal on Soil Biogeochemistry.

Snowpack plays an important role in winter soil processes by insulating the soil from freezing air temperatures, allowing C and N transformations to continue uninterrupted. The soil microbial community is responsible for the supply of nutrients in the spring; subniveal processes thus have important ramifications on nutrient availability post-melt. Climate models predict warmer winters with reduced snowpack, which influences soil microbial populations and nutrient transformations. Decreased snowpack offers less insulation, and the soil is more susceptible to freeze-thaw cycles.

We conducted a snow removal project in the Dwight Demeritt Forest of the University of Maine to examine the effects of decreased snowpack and increased frost on soil processes. Surface organic soil was collected from softwood plots during the late winter and early spring to track the changes as the system evolved from under the snowpack. Of the 8 plots sampled, 4 were kept clear of snow, and 4 were used as reference plots. Laboratory extractions and incubations were performed to quantify the inorganic available nitrogen (NH4⁺-N and NO3^--N), dissolved organic carbon (DOC), and potential net N-mineralization.

Snow removal resulted in decreased soil temperatures (2-8°C colder than the reference plots). DOC concentrations were synchronous with the vernal transition. The treatment plots had significantly higher DOC concentrations than the reference plots under the snowpack. The NH4⁺-N concentration changed over time in the treatment but not in the reference plots. The treatment plots also had higher ammonium concentrations than the reference plots.

Our findings demonstrated that freeze-thaw cycles play an important role in soil nutrient availability during the dynamic vernal transition of forest soils in northern latitudes. Understanding these processes becomes increasingly important to defining forest ecosystem response to a changing climate give the rapid changes that take place in the transition between winter and spring.