Quantification of Blue Carbon in Salt Marshes of the Pacific Coast of Canada

Tidal salt marshes are known to accumulate “blue carbon” at high rates relative to their surface area, which render these systems among the Earth’s most efficient carbon (C) sinks. However, the potential for tidal salt marshes to mitigate global warming remains poorly constrained because of the lack of representative sampling of tidal marshes from around the globe, inadequate areal extent estimations, and inappropriate dating methods for accurately estimating C accumulation rates. Here we provide the first estimates of organic C storage and accumulation rates in salt marshes along the Pacific Coast of Canada, within the Clayoquot Sound UNESCO Biosphere Reserve and Pacific Rim National Park Reserve, a region currently underrepresented in global compilations. Within the context of other sites from the Pacific Coast of North America, these young Clayoquot Sound marshes have relatively low C stocks but are accumulating C at rates that are higher than the global average, with pronounced differences between high and low marsh habitats. The average C stock calculated during the past 30 years is 54 ± 5 Mg C ha−1 (mean ± standard error), which accounts for 81 % of the C accumulated 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 global estimates of salt marsh C stocks, likely due to the shallow depth and young age 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 higher than 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 considered individual 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 Sound among NE Pacific Coast marsh studies. We attribute low CARs in the low marsh zones to shallow-rooting vegetation, reduced terrestrial sediment inputs, negative relative sea level rise in the region, and enhanced erosional processes. Per-hectare, CARs in Clayoquot Sound marsh soils are approximately 2–7 times greater than C uptake rates based on net ecosystem productivity in Canadian boreal forests, which highlights their potential importance as C reservoirs and the need to consider their C accumulation capacity as a climate mitigation co-benefit when conserving for other salt marsh ecosystem services.

An assessment of commercial fleet applications of management measures in Clayoquot Sound, British Columbia, Canada, aimed to mitigate whale watching impacts

The interactions between wildlife tourism operators and the animals that they rely on are complex. For commercial whale watching, the recognition of the potential disturbance from the vessels generates uncertainty regarding the effectiveness of management strategies for it to remain a ‘no-take’ practice. This warrants further evaluation. In this study, we analysed the activities of the whale watching fleet in Tofino, Vancouver Island, British Columbia, Canada, to evaluate industry sustainability and its ability to meet legislated conservation objectives. Visual observations gave context to an analysis of the communications of the fleet, made using Very High Frequency (VHF) marine radio. Transcription of these communications demonstrated three main themes; whale location, whale ‘transfers’ between operators, and encounter or ‘show’ quality. Cumulative encounter times from the fleet far exceeded the 30-minute limit recommended in the whale watching guidelines. Killer whales (Orcinus orca) were subject to the longest periods of vessel presence, with an average time spent in active encounters of 4.21 ±1.96 hours. This extended to almost the full operating day if whales remained within a feasible travelling distance of Tofino. Humpback (Megaptera novaeangliae) and gray whale (Eschrichtius robustus) encounters also exceeded the suggested time limit by 2.40 ± 1.73 hours and 1.31 ±1.07 hours, respectively. Increased education and the addition of spatial and temporal restrictions in management regimes could address the shortcomings of the current system to minimize potential disturbance to whales from commercial whale watching encounters and facilitate sustainable industry practices.

Carbon Stocks and Accumulation Rates in Salt Marshes of the Pacific Coast of Canada

Tidal salt marshes are known to accumulate blue carbon at high rates relative to their surface area and have been put forth as a potential means for enhanced CO2 sequestration. However, estimates of salt marsh carbon accumulation rates are based on a limited number of marshes globally and the estimation of carbon accumulation rates require detailed dating to provide accurate estimates. We address one data gap along the Pacific Coast of Canada by estimating carbon stocks in 34 sediment cores and estimating carbon accumulation rates using 210Pb dating on four cores from seven salt marshes within the Clayoquot Sound UNESCO Biosphere Reserve and Pacific Rim National Park Reserve of Canada (49.2° N, 125.80° W). Carbon stocks averaged 80.6 ± 43.8 megagrams of carbon per hectare (Mg C ha−1) between the seven salt marshes, and carbon accumulation rates averaged 146 ± 102 grams carbon per square meter per year (g C m−2 yr−1). These rates are comparable to those found in salt marshes further south along the Pacific coast of North America (32.5–38.2° N) and at similar latitudes in Eastern Canada and Northern Europe (43.6–55.5° N). The seven Clayoquot Sound salt marshes currently accumulate carbon at a rate of 54.28 Mg C yr−1 over an area of 46.94 ha, 87 % of which occurs in the high marsh zone. On a per-hectare basis, Clayoquot Sound salt marsh soils accumulate carbon at least one order of magnitude more quickly than the average of global boreal forest soils, and approximately two times larger than rates for forests in British Columbia. However, because of their relatively small area, we suggest that their carbon accumulation rate capacity could best be considered as a climate mitigation co-benefit when conserving for other salt marsh ecosystem services.