Valuing Carbon Stocks across a Tropical Lagoon after Accounting for Black and Inorganic Carbon: Bulk Density Proxies for monitoring

Abstract

3Managing seagrass and mangrove can be enhanced through carbon valued payment 1 4 incentives schemes. Success will depend on the accuracy and extent of the carbon stock 1 5 mitigation and accessible methods of monitoring and marking changes. In a relatively 1 6 closed socioecological Southeast Asian lagoon we estimated the value of total organic 1 7 carbon stocks (TOC) of both seagrass and mangroves. Mitigation corrections were also 1 8 made for black carbon (BC) and calcareous inorganic carbon equivalents (PIC equiv ), and 1 9 their sediment dry bulk density (DBD) tested as a cost effective means of both estimating 2 0 those stock concepts and possible impacts outside their parameter confidence intervals. 2 1 Overall, seagrass and mangroves TOC densities across the lower lagoon ranged from 2 2 15.3±4.3 and 124.3±21.1 Mg C ha -1 respectively, 175.2±46.9 and 103.2±19.0 Mg C ha -1 2 3 for seagrass and 355.0±24.8 and 350.3±35.2 Mg C ha -1 ) for mangroves across the two 2 4 upper lagoon branches. Only mangrove biomass made significant additional 2 5 contributions ranging from 178.5±62.3 to 120.7±94.8 Mg C ha -1 for lower and upper 2 6 regions respectively. The difference between the lagoons total seagrass and mangroves 2 7 TOC stocks (5.98±0.69 and 390±33.22 GgC respectively) was further amplified by the 2 8 lagoons' larger mangrove area. When corrected for BC and PIC equiv , the carbon stock 2 9 mitigation was only reduced by a moderate 14.2%. Across the lagoon the sedimentary 3 0 DBD showed strong (R 2 = 0.85, P < 0.001) to moderate (R 2 = 0.67, P < 0.001) linear 3 1 correlations with seagrass and mangrove [TOC] respectively, moderate correlations with 3 2

A re-evaluation of wetland carbon sink mitigation concepts and measurements: A diagenetic solution

“…The tropical seagrass meadow occupied the upper embayment of the Salut Mengkbong lagoon, located north of Kota Kinabalu, Sabah, a major population centre. The meadow was a subaquatic shallow system composed entirely of Enhalus sp., in which around a quarter of the leaf length could be seen floating on the water surface during spring low tides (Gallagher et al, 2020). The surface waters were generally turbid due to tidal washout out from the surrounding mangrove shoreline.…”

“…However, for the core taken from the Salut seagrass meadow, the baseline sedimentation was interrupted by a deposition storm surge event down from 23 cm and likely greater than 52 cm, the bottom core sample . Nevertheless, for completeness, we assume that the organic stock to 23 cm today is typical of past values, and around half the stock when integrated to 1 m (Gallagher et al, 2020;Lavery et al, 2013).…”

“…Similarly, for Mangrove forest at Chelem station 9, it is assumed that the organic stocks today are typical and approximated to twice the amount stored to 42 cm (Donato et al, 2011;Gallagher et al, 2020). the seagrass meadow (11%) comes from direct measurements.…”

Inorganic and Black Carbon Hotspots Constrain Blue Carbon Mitigation Services Across Tropical Seagrass and Temperate Tidal Marshes

“…However, the use of total organic carbon (TOC) for sequestration and stock assessments has recently been in question. Traditional assessments have largely failed to remove allochthonous organic recalcitrants from the equation (Gallagher 2014;Gallagher 2015;Gallagher 2017; Chew and Gallagher 2018; Chuan et al 2020;Gallagher et al 2020 ). These stable organic forms are not produced by the blue carbon ecosystem; deposition within the ecosystems' sediments does not afford additional protection from remineralization.…”