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Snow and snowpack controls on deep-soil carbon storage in northern forest soils

Soils are one of the largest reservoirs for carbon (C) worldwide, holding 2-3 times as much C as the atmosphere. Much of this C resides in poorly-studied deep soil horizons (>30 cm in depth), that have generally been viewed as stable over time. However, recent research has shown that C stored in deep soil horizons can be lost as carbon dioxide (CO2) to the atmosphere due to changes in land management or plant productivity. In this research project investigators will test a new hypothesis that deep soil C storage in northern forests is enhanced by the transport of C through the soil profile by melting snowpacks. If true, declining snowpacks may represent a positive feedback mechanism to global climate change, by reducing C storage in deep soil horizons and adding to atmospheric C stores. Their hypothesis is based on strong positive relationships between winter snowpack depth and deep-soil C storage across lake-effect snowfall gradients in the Great Lakes Region, USA. Investigators will test their hypothesis using two complimentary approaches. First, they will examine the distribution and chemical composition of soil C across three naturally-occurring, lake-effect snowfall gradients in the Upper Great Lakes region. Second, they will conduct intensive measurements of fluxes of dissolved C through soil in response to naturally-occurring annual variation in snowfall, as well as experimentally-imposed snow removal and snow augmentation treatments. Evidence that would support their hypothesis includes: 1) Deep soil horizons in high snowfall areas have higher concentrations of C with chemical signatures indicating that it is derived from surface plant litter, 2) Deep soil horizons from low-snow areas have low C concentrations with chemical signatures indicating that it is derived from roots or microbial metabolism, and 3) Experimental manipulation of snowpack depth results in predictable changes in the transport and retention of C from surface plant litter to deep soil horizons. This project will advance fundamental understanding of climatic controls over soil C cycling processes, as well as contributing to soil genesis theory. Understanding the nature and underlying mechanisms of snowpack effects on soil C dynamics is particularly important, given that snowfall amounts, duration of snow on the ground, and snowpack thickness are all components of climate that are likely to be greatly impacted in the next few decades, as climate warms and winters become less snowy.

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