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Forest Canopies Influence the Deposition and Concentration of Debris, Lightabsorbing Impurites, and Pollutants in the Sierra Nevada Snowpack
Submitted by ecourtri on Wed, 03/18/2020 - 13:04
|Forest Canopies Influence the Deposition and Concentration of Debris, Lightabsorbing Impurites, and Pollutants in the Sierra Nevada Snowpack
|Year of Conference
|Gleason, Kelly E., McConnell Joseph R., Arienzo Monica M., Chellman Nathan, Hedge Christine, and Harpold Adrian
|87th Annual Western Snow Conference
|accelerated snowmelt, black carbon, canopy debris, pollutant concentrations, Sagehen Experimental Forest, snow albedo
Forests are typically warmer than surrounding open areas, particularly in warm mid-latitude climates, and forest canopies radiate longwave radiation throughout the winter, driving mid-winter snowmelt throughout the snow accumulation period. During winter, forest canopies shed organic debris onto the snowpack below, which concentrates on the snow surface during snowmelt, and may further accelerate snowmelt due to reduced snow albedo. Snowpack, as long as it remains frozen, serves not only as a reservoir of water, but also as a time-resolved repository of local and regionally-sourced particles, including black carbon (BC), dust, organic debris, and pollutants. We evaluated how forests may alter the depositional process of particles and pollutants into the snowpack beneath forest canopies, as well as how warm conditions in forests influence the redistribution of particles and pollutants in the snowpack. We measured BC, dust, organic debris, and the elemental composition of pollutants throughout snowpacks in an open meadow and beneath a nearby pine forest each month during winter and early spring of 2017 at the Sagehen Experimental Forest in the Northern Sierra Nevada Mountains.
Overall, snowpacks under the forest canopy had much greater concentrations of organic and inorganic debris, which concentrated on the snowpack surface throughout the snow season. While concentrations of BC, dust, and pollutants were similar under the forest canopy and in the open meadow during winter. During spring snowmelt, BC and dust became concentrated on the snowpack surface under the forest canopy and in the open meadow. Phosphorus and sulfur concentrations were greater under the forest canopy, while bismuth was greater in the open meadow during spring snowmelt. Nitrate concentrations on the snowpack surface were similar between sites, but reduced earlier in the meadow likely due to enhanced photodegradation. Throughout the snowpack season, debris, BC, dust and pollutants were much more variable under the forest canopy than the open meadow. Forest canopies serve as a source of large debris to the snowpack, but have little influence over the deposition and concentration of more regionally sourced light absorbing particles in the snowpack, and differential influence on the deposition and concentration of pollutants in the snowpack.