Soil Freezing Effects on Sources of Nitrogen and Carbon Leached During Snowmelt
2014
Campbell, John L. | Reinmann, Andrew B. | Templer, Pamela H.
Soil freezing in winter has been shown to enhance growing season losses of C and N in northern forests. However, less is known about effects of soil freezing on C and N retention during snowmelt and the sources of C and N leached, which is important because losses to stream water are greatest during this period. Organic horizon soils (Oi + Oe + Oa) from the Hubbard Brook Experimental Forest in New Hampshire, United States were placed in columns in a laboratory experiment and subjected to one of three different temperature treatments (+5.0, −0.5, and −15.0°C) before they were covered with snow and placed in a +5.0°C cold room to induce snowmelt. Results for all temperature treatments showed that fluxes of all forms of C and N declined over snowmelt, indicating flushing of a limited soil pool. The quality of dissolved organic matter (DOM) became increasingly aromatic, while δ¹⁵N-NO₃– declined, indicating that as labile organic matter and N become less available during snowmelt, a greater proportion of N is cycled through the microbial pool. Mild soil freezing had little effect on C and N processing; however, severe soil freezing resulted in delayed leaching and a flush of labile DOM. The severely frozen soils also leached significantly less dissolved inorganic N (DIN; NH₄⁺ and NO₃–), likely due to the inhibitory effect of extremely cold soil temperatures on microbial production. These results highlight the importance of winter climate in regulating fluxes and sources of C and N leached during snowmelt, having implications for stream water quality.
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