Quantification of blue carbon in salt marshes of the Pacific coast of Canada

[摘要] Tidal salt marshes are known to accumulate “bluecarbon” at high rates relative to their surface area, which render thesesystems among the Earth's most efficient carbon (C) sinks. However, thepotential for tidal salt marshes to mitigate global warming remains poorlyconstrained because of the lack of representative sampling of tidal marshesfrom around the globe, inadequate areal extent estimations, andinappropriate dating methods for accurately estimating C accumulation rates.Here we provide the first estimates of organic C storage and accumulationrates in salt marshes along the Pacific coast of Canada, within the United Nations Educational, Scientific and Cultural Organization (UNESCO) Clayoquot Sound Biosphere Reserve and Pacific Rim National ParkReserve, a region currently underrepresented in global compilations. Withinthe context of other sites from the Pacific coast of North America, theseyoung Clayoquot Sound marshes have relatively low C stocks but areaccumulating C at rates that are higher than the global average withpronounced differences between high and low marsh habitats. The average Cstock calculated during the past 30 years is 54  ±  5 Mg C ha −1 (mean  ±  standard error), which accounts for 81 % of the Caccumulated to the base of the marsh peat layer (67  ±  9 Mg C ha −1 ) . The total C stock is just under one-third of previous globalestimates of salt marsh C stocks, likely due to the shallow depth and youngage of the marsh. In contrast, the average C accumulation rate (CAR) (184  ±  50 g C m −2  yr −1 to the base of the peat layer) is higherthan both CARs from salt marshes along the Pacific coast (112  ±  12 g C m −2  yr −1 ) and global estimates (91  ±  7 g C m −2  yr −1 ) . This difference was even more pronounced when we consideredindividual marsh zones: CARs were significantly greater in high marsh (303  ±  45 g C m −2  yr −1 ) compared to the low marsh sediments (63  ±  6 g C m −2  yr −1 ) , an observation unique to Clayoquot Soundamong NE Pacific coast marsh studies. We attribute low CARs in the low marshzones to shallow-rooting vegetation, reduced terrestrial sediment inputs,negative relative sea level rise in the region, and enhanced erosionalprocesses. Per hectare, CARs in Clayoquot Sound marsh soils areapproximately 2–7 times greater than C uptake rates based on net ecosystemproductivity in Canadian boreal forests, which highlights their potentialimportance as C reservoirs and the need to consider their C accumulationcapacity as a climate mitigation co-benefit when conserving for other saltmarsh ecosystem services.

[学科分类] 大气科学