Landslides, a forest disturbance, mobilize carbon (C) sequestered in vegetation and soils. Mobilized C is deposited either onto hillslopes or into the water, sequestering C from and releasing C to the atmosphere at different time scales. The C‐dense old‐growth temperate forests of SE Alaska are a unique location to quantify C mobilization rate by frequent landslides that often evolve into saturated moving masses known as debris flows. In this study, the amount of C mobilized by debris flows over historic time scales was estimated by combining a landslide inventory with maps of modeled biomass and soil carbon. We analyzed SE Alaskan landslides over a 55‐year period where a total of 4.69 ± 0.21 MtC was mobilized, an average rate of 2.5 tC km−2 yr−1. A single event in August 2015 mobilized 57,651 ± 3,266 tC, an average of 63 tC km−2. Depositional fate was inferred using two methods, a standard stream intersection analysis and a second novel approach using simulated debris flow deposition modeling calibrated to the study area. Approximately 60% of debris flow deposits intersected the stream network (9% into mainstem channels, 91% into small tributaries), consistent with long‐term modeled connectivity, suggesting that debris flows are likely to contribute to globally significant amounts of C buried in local fjord sediments. Our results are consistent with an emerging consensus that landslide disturbances that mobilize organic carbon may play an important role in the global carbon cycle over geologic time, with coastal temperate forests being hotspots of potential carbon sequestration.
Landslides influence the global carbon (C) cycle by facilitating transfer of terrestrial C in biomass and soils to offshore depocenters and redistributing C within the landscape, affecting the terrestrial C reservoir itself. How landslides affect terrestrial C stocks is rarely quantified, so we derive a model that couples stochastic landslides with terrestrial C dynamics, calibrated to temperate rainforests in southeast Alaska, United States. Modeled landslides episodically transfer C from scars to deposits and destroy living biomass. After a landslide, total C stocks on the scar recover, while those on the deposit either increase (in the case of living biomass) or decrease while remaining higher than if no landslide had occurred (in the case of dead biomass and soil C). Specifically, modeling landslides in a 29.9 km2watershed at the observed rate of 0.004 landslides km−2 yr−1decreases average living biomass C density by 0.9 tC ha−1(a relative amount of 0.4%), increases dead biomass C by 0.3 tC ha−1(0.6%), and increases soil C by 3.4 tC ha−1(0.8%) relative to a base case with no landslides. The net effect is a small increase in total terrestrial C stocks of 2.8 tC ha−1(0.4%). The size of this boost increases with landslide frequency, reaching 6.5% at a frequency of 0.1 landslides km−2 yr−1. If similar dynamics occur in other landslide‐prone regions of the globe, landslides should be a net C sink and a natural buffer against increasing atmospheric CO2levels, which are forecast to increase landslide‐triggering precipitation events.
more » « less- Award ID(s):
- 1711986
- NSF-PAR ID:
- 10425382
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Biogeosciences
- Volume:
- 128
- Issue:
- 6
- ISSN:
- 2169-8953
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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