The extent and thickness of the peat in the region is variable. Research conducted by Maloney in the 1970s documented areas with peat thickness up to 10 meters. Meanwhile, a Master's thesis by Rio Tarigan from IPB University reported an average thickness of 2.5 meters, with a surface bulk density of 0.28 g/cm³ and a carbon content of 56%. However, the exact location of this data was not provided.
In contrast, a Bachelor's thesis by Grandis Sitanggang from Universitas Sumatera Utara (USU) reported peat thickness between 0.6 to 1 meter. The study estimated an overall area of approximately 6,900 hectares across three regions: Dolok Sanggul (2,800 hectares), Pollung (1,600 hectares), and Lintong Nihuta (1,800 hectares), based on the existing geology map. The actual extent of the areas is likely larger.
A more recent study by Munawaroh et al. (2022) show that the C content of peatlands in Pllung and Dolok Sanngul has declined, with a maximum of 22% on an open peatland (with no vegetation) and 5% on coffee fields.
Table 1. Soil properties of peatland in Pollung and Dolok Sanggul with different land uses ( Munawaroh et al., 2022)
Land Type | Organic C (%) | pH | C/N | Water content (%) |
Open peatland | 22.05 | 2.7 | 37.37 | 98.0 |
Grassland | 19.32 | 4.1 | 30.18 | 42.8 |
Paddy field | 14.15 | 4.2 | 22.46 | 28.1 |
Onion field | 15.64 | 3.7 | 22.66 | 32.8 |
Coffee field | 5.23 | 3.6 | 10.25 | 14.3 |
Environmental Degradation
The Desa Nagasaribu region in Lintong Nihuta was previously mined for fuel by locals to supply a local pulp and paper mill, Indorayon or Toba Pulp Lestari, in 1996. This process involved draining the area, which is still evident as water continues to flow out from the drain. While mining has been halted due to local government regulations introduced in 2013, the area has not been rehabilitated. Locals continue to collect wood from the area, which they use for making charcoal via open fire burning. A study from USU indicated that this practice of using peat as fuel and open-burning it contributes significantly to pollution.
Several problems have arisen from this drainage:
- It has exposed peats to oxidation and subsidence, leading to substantial CO2 emissions.
- The water supply to local traditional paddy fields has been reduced, causing some farmers to experience drying out of their fields source.
- Biodiversity loss has been reported.
- The practice of open fire burning to make charcoal from collected wood contributes to air pollution source.
- The dry peatland condition poses a significant fire hazard source.