Climate-driven changes in organic carbon export from coastal temperate rainforest watersheds
Thursday, 26 January 2017: 09:20
Ballroom III-IV (San Juan Marriott)
Eran W Hood1, Jason Fellman1, Durelle Scott2, Michael Q Nassry3, Sonia A Nagorski1 and Robert G Spencer4, (1)University of Alaska Southeast, Juneau, AK, United States, (2)Virginia Polytechnic Institute and State University, Blacksburg, VA, United States, (3)Pennsylvania State University Main Campus, University Park, PA, United States, (4)Florida State University, Department of Earth, Ocean and Atmospheric Sciences, Tallahassee, FL, United States
Abstract:
Coastal temperate rainforest (CTR) watersheds in Coast Mountains of southeast Alaska have dense soil carbon stocks (~300 Mg C ha
-1) and high specific discharge (1.5-7 m yr
-1) driven by frontal storms from the Gulf of Alaska. As a result, dissolved organic carbon (DOC) fluxes from Alaskan CTR watersheds are among the highest of any ecoregion on Earth, with a regional DOC flux exceeding 2 Tg yr
-1. Climate warming is having a variety of impacts on CTR watersheds. Watershed landcover is being altered by glacier retreat, and as much as 60% of the region’s 20,000+ km
2 of glaciers are expected to be lost by 2100. In addition, precipitation in the North American CTR is projected to increase by 5-20% by the end of the century, with a concomitant increase in the intensity of storms and a decrease in the proportion of solid precipitation. Because stormflows resulting from extreme precipitation events have the potential to exert an outsized influence on annual organic carbon fluxes from CTR watersheds, these predicted climate-driven changes have important implications for the land-to-ocean flux of organic carbon (as DOC and POC) from CTR watersheds. Moreover, the impact of extreme precipitation events on organic carbon export will vary across both space and time as a result of the differences in the hydrology and biogeochemistry between glacierized and ice-free watersheds.
We sampled storm events across CTR watersheds spanning a glacier landcover gradient. Our results indicate that DOC export from forested, ice-free watersheds exhibits a strong flushing response that is not present in glacier-dominated watersheds. This finding suggests that future increases in large precipitation events may substantially increase regional DOC export and further that the impact of this phenomenon will be magnified by continuing glacier loss in large coastal watersheds. Our data also indicate that the speciation of organic carbon fluxes will be impacted by an increase in the magnitude and abundance of storm events. In particular, the ratio of POC:DOC export can be expected to increase over time, particularly in watersheds with little or no-glacier cover. Overall, our work suggests that climate warming will have both direct and indirect effects on land-to-ocean fluxes of organic carbon from CTR watersheds ranging from British Columbia to Alaska.
