Mapping peat thickness and carbon stocks of the central Congo Basin using field data

Abstract

The world's largest tropical peatland complex is found in the central Congo Basin. However, there is a lack of in situ measurements to understand the peatland's distribution and the amount of carbon stored in it. So far, peat in this region has been sampled only in largely rain-fed interfluvial basins in the north of the Republic of the Congo. Here we present the first extensive field surveys of peat in the Democratic Republic of the Congo, which covers two-thirds of the estimated peatland area, including from previously undocumented river-influenced settings. We use field data from both countries to compute the first spatial models of peat thickness (mean 1.7 ± 0.9 m; maximum 5.6 m) and peat carbon density (mean 1,712 ± 634 MgC ha −1 ; maximum 3,970 MgC ha −1 ) for the central Congo Basin. We show that the peatland complex covers 167,600 km 2 , 36% of the world's tropical peatland area, and that 29.0 PgC is stored below ground in peat across the region (95% confidence interval, 26.3-32.2 PgC). Our measurement-based constraints give high confidence of globally significant peat carbon stocks in the central Congo Basin, totalling approximately 28% of the world's tropical peat carbon. Only 8% of this peat carbon lies within nationally protected areas, suggesting its vulnerability to future land-use change.

What determines peat swamp vegetation type in the Central Congo Basin?

“…We use the 50 m land-type classification map (figure 1) developed by Crezee et al (2022), together with terrain and climatological data to assess the drivers of differences in regional composition between the two major swamp vegetation types, palm and hardwood. To summarise, the terrain, climatological and weather data we use includes: the MERIT Hydro 90 m elevation and Height Above Nearest Drainage (HAND) basin (Yamazaki et al, 2017); Hydrobasins sub-basin delineations (Lehner and Grill, 2013); Climate Hazards center Infrared Precipitation with Stations (CHIRPS) rainfall (Funk et al, 2015a); CHPclim monthly rainfall climatology (Funk et al, 2015b); and CHIRTS maximum temperature (Funk et al, 2019).…”

“…(2017) measured peat depth for palm and hardwood swamps, with no significant difference found between the two. Peat depth has recently been more comprehensively mapped for the Cuvette Centrale region (Crezee et al, 2022), with slightly higher peat depth and carbon density predicted for palm swamp. This is likely because palm swamps are often located in the deeper interiors of peatland areas.…”

“…The Cuvette Centrale (Figure 1), situated in the central lowland region of the Congo Basin, is the second largest wetland in the tropics (Dargie et al, 2017) and contains the largest area of tropical peatland, with an estimated extent of 165,600 km 2 , and storing 29.0 Pg C (95% CI, 26.3-32.2 Pg C) (Crezee et al, 2022). It spans the Republic of Congo (RoC) and the Democratic Republic of Congo (DRC), with the Ubangi river marking the border between these two countries.…”

“…It spans the Republic of Congo (RoC) and the Democratic Republic of Congo (DRC), with the Ubangi river marking the border between these two countries. Crezee et al (2022). Dargie et al (2017) estimated that the Cuvette Centrale's carbon storage contribution increases the global carbon stock within tropical peatlands by 36% to 104.7 Pg C (within a 69.6 to 129.8 Pg C range).…”

“…Within this study our aim was to improve our understanding of climatic influences on the current distribution of Cuvette Centrale peatland vegetation. The peatland maps produced by Dargie et al (2017) and Crezee et al (2022) show that palmdominated swamp forest tends to occur in more interior peatland locations, with hardwood-dominated more towards the edge, delineated by the river system. We hypothesise that: 1. additional water input in the form of higher water tables and/or more extensive periods of water availability benefits palms, and that areas where palm dominates benefit from higher dry and/or wet season rainfall totals, and 2. palms may dominate at lower elevations to benefit from additional water input from ground water flow and pooling of water.…”