Total ecosystem carbon stocks at the marine‐terrestrial interface: Blue carbon of the Pacific Northwest Coast, United States

Abstract

The coastal ecosystems of temperate North America provide a variety of ecosystem services including high rates of carbon sequestration. Yet, little data exist for the carbon stocks of major tidal wetland types in the Pacific Northwest, United States. We quantified the total ecosystem carbon stocks (TECS) in seagrass, emergent marshes, and forested tidal wetlands, occurring along increasing elevation and decreasing salinity gradients. The TECS included the total aboveground carbon stocks and the entire soil profile (to as deep as 3 m). TECS significantly increased along the elevation and salinity gradients: 217 ± 60 Mg C/ha for seagrass (low elevation/high salinity), 417 ± 70 Mg C/ha for low marsh, 551 ± 47 Mg C/ha for high marsh, and 1,064 ± 38 Mg C/ha for tidal forest (high elevation/low salinity). Soil carbon stocks accounted for >98% of TECS in the seagrass and marsh communities and 78% in the tidal forest. Soils in the 0–100 cm portion of the profile accounted for only 48%–53% of the TECS in seagrasses and marshes and 34% of the TECS in tidal forests. Thus, the commonly applied limit defining TECS to a 100 cm depth would greatly underestimate both carbon stocks and potential greenhouse gas emissions from land‐use conversion. The large carbon stocks coupled with other ecosystem services suggest value in the conservation and restoration of temperate zone tidal wetlands through climate change mitigation strategies. However, the findings suggest that long‐term sea‐level rise effects such as tidal inundation and increased porewater salinity will likely decrease ecosystem carbon stocks in the absence of upslope wetland migration buffer zones.

Blue Carbon Stocks and Exchanges Along the Pacific West Coast

“…Recent studies of the U.S. west coast and of conterminous U.S. tidal wetlands allow for comparison with salt marsh data collected here. Much like with seagrass meadows, California salt marsh carbon storage was also higher than previous estimates from the U.S. west coast (Kauffman et al, 2020;Table 3). Both the data presented here as well as those from Kauffman et al (2020) (Table 3) were collected from similar marsh zones and species compositions, reducing some potential for these factors to result in the observed differences in carbon stocks.…”

“…Much like with seagrass meadows, California salt marsh carbon storage was also higher than previous estimates from the U.S. west coast (Kauffman et al, 2020;Table 3). Both the data presented here as well as those from Kauffman et al (2020) (Table 3) were collected from similar marsh zones and species compositions, reducing some potential for these factors to result in the observed differences in carbon stocks. Previous work has found that high-marsh zone sediments are likely to contain greater OC than mid-and lower-marsh zones, and that less inundation can facilitate increased root productivity and increased OC (the sites presented here would be considered 'lower-marsh zones') (Blum, 1993;Connor et al, 2001;Zhou et al, 2007).…”

“…Eelgrass (Zostera marina) is the dominant seagrass species in North America and occupies coastal waterways from Alaska to Mexico (Green & Short, 2003). Until recently, seagrass carbon stock data were almost entirely absent along the west coast of North America (See Capece et al, 2019;Kauffman et al, 2020;O'Donnell et al, 2017;Poppe & Rybczyk, 2018;Postlethwaite et al, 2018;Röhr et al, 2018). Of these studies, very few data came from Central or Southern California seagrass meadows, despite the fact that this region represents a key https://doi.org/10.5194/bg-2021-27 Preprint.…”

Climate-Mediated Changes to Linked Terrestrial and Marine Ecosystems across the Northeast Pacific Coastal Temperate Rainforest Margin

“…Hereafter, NPCTR will refer to these two subregions. Within the NPCTR, large and long-lived conifers, abundant peatland ecosystems, and deep soils store some of the highest amounts of C globally (combined above- and belowground, more than 1000 megagrams [Mg] per hectare [ha]; Smithwick et al 2002 , McNicol et al 2019 , Kauffman et al 2020 ). The landscape has been largely shaped by several episodes of glaciation, combined with uplift and erosional processes, leading to a complex pattern of islands, incised coastal mountain ranges, fjordlands, wide glacial valleys, and lowlands.…”

Comment on bg-2021-27

“…Salt marsh carbon stocks are similarly understudied in western North America, with published carbon stock data from only four estuaries in the region and very minimal spatial coverage and analyses performed in three of these locations (Brevik and Homburg, 2004;Callaway et al, 2012;Kauffman et al, 2020;Patrick and DeLaune, 1990). Existing analyses of North American freshwater wetlands and salt marshes are typically dominated by studies along the east coast (Nahlik & Fennessy, 2016;Wilkinson et al, 2018; with the exception of Holmquist et al 2018).…”