Comparison of Landscape-Level Fire and Carbon Transfer Histories from a Retrospective Carbon Budget Model to those from Sediment Records, Sooke Lake Watershed, British Columbia, Canada.
Abstract
A retrospective carbon (C) budget for the 8500 ha Sooke Lake Reservoir (SLR) watershed from 1911 - 2012 was developed using historic spatial inventory, disturbance data and a spatially-explicit version of the Carbon Budget Model-Canadian Forest Sector-3. Stream flow and dissolved C [DOC] data from 1996-2012 for three catchments were used to parameterize the model fraction of decay losses from humified soil C to CO2 and DOC. The model estimated terrestrial C exports from the watershed to the reservoir. A 33 cm sediment gravity core was collected from SLR in 72m water and sampled at 0.5cm resolution. An age model developed using Pb-210 and 14C dates revealed that the core spanned a 300 yr period, with the top 11.5cm from 1911-2014 CE. Charcoal and magnetic susceptibility records were used to estimate fire frequency and erosion. Terrestrial C inputs to the sediment were estimated by Pyrolysis Gas Chromatography Mass Spectroscopy (pyGCMS) of C compounds. Charcoal was variable, with peaks at 29, 22, 18, 16, 14, 11, 8, 5 and 2 cm depth. Charcoal peaks in the 1920's, 1930's, 1980's, 2000's occur ~10 years after nearby fire events, whereas magnetic peaks occur ~10 years after forest clearing for reservoir expansion (1915, 1970, 2002). Known fire events associated with clearing, suggest foreshore charcoal washed into the SLR. Although post-harvest burns occurred within the watershed 250-4000m from the core location, no matching charcoal peaks were detected. A longer sediment core from nearby Begbie Lake reveals that fire return intervals averaged 310 years from 2700yr BP to present, nearly identical to the 300yr default fire return used for the ~5000yr spin-up for model runs. In the SLR core, both total C and %C declined from 1911-2014, likely due to increased inputs of mineral soil from human activity. Over 160 C compounds were identified in the core, with many close to detection limit. Initial analysis using 2 terrestrial and 2 algal C markers showed % terrestrial C was close to 0% at upper depths to >50% at lower depths. Total terrestrial C sequestered in reservoir sediments using 4 markers, was estimated (6124 Mg C/100yr) as 20% of model estimates of DOC exports (30640 Mg C/100yr). Results will be presented from a repeated pyGCMS analysis using higher sample volumes, especially those with low %C values, and an improved C compound library.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.B43I2597T
- Keywords:
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- 0428 Carbon cycling;
- BIOGEOSCIENCES;
- 0458 Limnology;
- BIOGEOSCIENCES;
- 0495 Water/energy interactions;
- BIOGEOSCIENCES;
- 1818 Evapotranspiration;
- HYDROLOGY