We estimate that pre-settlement wetlands held up to ~ 3.3 Pg of carbon relative to ~ 1.3 Pg for present-day (total across all wetland classes).
If those small wetlands (< 1 ha) could be fully mapped for pre-settlement wetlands, the loss ratio might be higher than the estimated 55.8%.
This study contrasts two periods of natural wetlands: one before European settlement ('pre-settlement wetlands' in 1800 CE) and the other with modern-day land use (surveyed in 2011).
Our effort to include small wetlands (< 10 ha) in our pre-settlement reconstruction increased the total estimated extent of pre-settlement wetlands by 25% compared to previous work [15, 16].
Of this total, the extent of pre-settlement wetlands was estimated at ~ 24,984 km2 (~ 30% of total land cover), reflecting the sum of the current wetlands (~ 11,032 km2) and converted wetlands (~ 13,953 km2) as in Table 1.
Because obtaining the maximum potential area of Holocene natural (pre-settlement) wetlands and carbon storage was our objective, the 2011 wetland map was used to adjust the DUC's pre-settlement map.
Wetland conversion was identified by areas where the pre-settlement wetlands overlap with non-wetland areas in the modern day (2011 CE) land use map (Additional file 1: Figure S1).
Fig. 2 Map overlay results showing a distribution of pre-settlement wetlands colour coded by wetland class, b current wetlands colour coded by wetland class, and c current land cover classification for converted wetlands, coloured by land use type.
DUC pre-settlement wetland reconstruction was made available through a data-sharing agreement.
Agricultural land use is the most common driver of the pre-settlement wetland conversion regardless of the wetland type (Table 1), but there are some local exceptions.
A very small proportion of the pre-settlement wetland removal is in fact attributable to direct peat extraction (1.8% of the total 'Developed' in Table 2).
