The Effect of Soil Freezing On Nitrogen Dynamics: A Snow Manipulation Study in a Forested Watershed in the Snow Belt of Western New York, USA.

The importance of understanding winter ecology is accentuated by concerns about how ecosystems will respond to climate change. Although climatic models of north temperate ecosystems predict greater amounts of winter precipitation in the future, reductions in snowpack are likely to occur due to the increased importance of thaws, sleet, and rain-on-snow events.  Without an insulating snowpack, soil ice formation at the onset of winter will persist throughout the winter and/or more frequent freeze-thaw cycles will occur and could affect soil nutrient cycling.  Understanding the effects of soil freezing dynamics on soil processes such as nitrification is important since nitrate is the most mobile form of N, and production of it in the soil during winter can result in substantial N leaching to surface waters during spring snowmelt.  In this study, we manipulated the snowpack depth to test the effects of soil freezing on in situ rates of nitrification and N mineralization with reference and snow manipulation treatment plots at Point Peter Brook Watershed (PPBW), located in the snow belt of western, NY.  One pair of treatment and reference plots was located in the riparian zone of PPBW while another pair was located on the hillslope.  The snow manipulation treatment induced soil freezing that lasted over the entire winter in both treatment plots.  The treatment plots at both landscape positions had significantly greater N mineralization than reference plots.  No treatment effect was observed for nitrification in the riparian plots while the hillslope treatment plot had a greater nitrification rate than the reference hillslope plot.  As climate change alters temperate forested ecosystems, especially during winter, the effect of soil freezing should be considered when evaluating differences in N dynamics in temperate forested ecosystems.