An opinion on BlueCAM an Australian blue carbon method to estimate climate change mitigation benefits of coastal wetland restoration by Lovelock et al. (2022)

Abstract

BlueCAM is an Australian coastal wetland restoration methodology for estimating atmospheric warming abatement. However, BlueCAM is incomplete and contains conceptual and formulation errors. Conceptually, sequestration may be understated by not accounting for an increase in animal biomass and baseline ecosystems as heterotrophic carbon sources. Or, more likely, sequestration services are significantly overestimated by not considering: (1) remineralization of allochthonous carbon, supplied from surrounding ecosystems; (2) the subtraction of a notable intrinsically recalcitrant allochthonous carbon fraction; (3) whether baseline ecosystems are autotrophic carbon sinks; and (4) the reduction in air–sea flux during periods of submersion. Erroneously, BlueCAM: (1) implies that any remains of labile allochthonous carbon should be subtracted from stocks, not just the recalcitrant fraction; and (2) does not embed additional warming from CH4 emissions within components of net ecosystem production. Taken together, these errors are likely to greatly overestimate both wetland sequestration and warming abatement services.

Response to Gallagher (2022)—the Australian Tidal Restoration for Blue Carbon method 2022—conservative, robust, and practical

“…The contributors to method development had expertise from a range of disciplines, as well as from across the geographic diversity of Australian coastal wetlands. Gallagher (2022) provided commentary on the Tidal Restoration for Blue Carbon method 2022 and BlueCAM, described in Lovelock et al (2022). Here we provide clarification of points made by Gallagher (2022).…”

“…Gallagher (2022) provided commentary on the Tidal Restoration for Blue Carbon method 2022 and BlueCAM, described in Lovelock et al (2022). Here we provide clarification of points made by Gallagher (2022).…”

“…likely to underestimate, rather than overestimate, carbon abatement outcomes). While some of the points raised by Gallagher (2022) are scientifically interesting (see below), they did not consider the broader context of method development (e.g. that abatement methods are consistent with national and Intergovernmental Panel on Climate Change [IPCC] greenhouse gas inventory reporting standards, as well as the Australian legislative offsets integrity standards), or the practical implementation of a method.…”

“…that abatement methods are consistent with national and Intergovernmental Panel on Climate Change [IPCC] greenhouse gas inventory reporting standards, as well as the Australian legislative offsets integrity standards), or the practical implementation of a method. Some points raised by Gallagher (2022) arise from incorrect interpretation of BlueCAM.…”

“…Saintilan et al 2013; Needelman et al 2018; Geraldi et al 2019). As tidal wetland restoration projects are implemented nationally, future assessments of autochthonous vs. allochthonous carbon in restored coastal wetlands as well as research on fluxes of carbon among coastal wetlands, rivers and coastal oceans will enhance our understanding of variation in the extent of lateral transport of carbon in the coastal zone, which could contribute to future revisions of IPCC Guidance and the BlueCAM model. Does not subtract slowly decomposing carbon fractions (referred to in Gallagher (2022) as “recalcitrant” or “black” carbon). …”