Air temperature and length of snowpack season describe annual DOC mobilization variability across a climate transect of mesic boreal forest sites
Abstract
The mobilization of soil dissolved organic carbon (DOC) is an important component of the terrestrial to aquatic (T-A) carbon flux. Controls on the T-A flux are difficult to define because of complex interactions between hydrological and biogeochemical processes operating at different temporal and spatial scales. In seasonally snow-covered environments, the snowpack holds both biogeochemical and hydrological significance as insulator of the soil during winter and container of a large proportion of the annual precipitation that is released during spring melt. This four-year study was conducted within three maritime balsam fir forests spanning 47 ° N to 53 ° N. Mean annual precipitation (1074 mm to 1340 mm) and mean annual temperature (0 ° C to 5 ° C) increase with decreasing latitude. All three forests are consistently snow-covered throughout winter and reach depths sufficient to protect soils from frost, however, there is a decrease in the amount of snowfall (462 to 393 cm), and decrease in the length of the snowpack season (160 days to 109 days) from north (N) to south (S). Mean annual DOC mobilization increased from N to S but, surprisingly, there was no relationship between annual DOC mobilization and annual precipitation while there was a positive relationship with temperature at all sites. To interpret this unexpected result, a series of ecosystem specific hydrometeorological indices were defined and ranked, including those capturing productivity, precipitation event size and snowpack dynamics. Of the 16 models ranked, air temperature, snowpack duration and snowfall best described DOC variability interannually and across sites. Air temperature and snowpack duration were highly correlated, suggesting that air temperature indirectly affects DOC mobilization through a direct control on snowpack season length in these forests. Both warmer years and sites have shorter snowpack seasons and mobilize more DOC, implying that these boreal forest soils are larger sources of C to aquatic networks under warmer conditions. Although the "colder soils in a warmer world" phenomena is of concern in many boreal regions experiencing increased occurrence of soil frost, observations from these systems are more likely explained by a combination of reduced winter heterotrophic soil C losses and increased soil water infiltration.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2020
- Bibcode:
- 2020AGUFMB046.0011B
- Keywords:
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- 0414 Biogeochemical cycles;
- processes;
- and modeling;
- BIOGEOSCIENCES;
- 0428 Carbon cycling;
- BIOGEOSCIENCES;
- 0495 Water/energy interactions;
- BIOGEOSCIENCES