Hydrological Fluxes From a Drained Tropical Peatland: Evapotranspiration Consistent Despite Large Fluctuations in Precipitation and Soil Moisture

Abstract

Tropical peatlands play a critical role in regional water cycling, yet most tropical peat swamp forests (PSFs) are anthropogenically disturbed through modification of the water table (e.g., drainage), deforestation, and fire events. These disturbances can alter ecosystem processes including evapotranspiration (ET), thereby creating feedbacks that degrade peatland ecosystem services and result in significant alteration of greenhouse gas budgets. However, our understanding of fine-scale hydrological fluxes in tropical peatland ecosystems is currently limited. Here, therefore, we aimed to quantify rates of ET from a degraded tropical PSF in Central Kalimantan, Indonesia, in the context of broader peatland hydrology and site meteorology. From March to November 2020, ET ranged from 1.8 to 7.3 mm d⁻¹, averaged 4.1 ± 0.1 mm d⁻¹ and was consistent between months, despite large fluctuations in precipitation (P) following typical wet/dry seasonality (e.g., 4.1 ± 0.2 mm d⁻¹ in July, compared to 17.5 ± 4.4 mm d⁻¹ in April). Total ET over the nine-month study period was 1127 mm; approximately 37% of total precipitation. Daily ET rates were comparable to previous studies from tropical PSFs; however, the ratio of ET/P was lower than other tropical PSF sites. We suggest that the volume of water lost through canal drainage may be higher at this site than other tropical PSFs, indicating more substantial hydrological alteration through drainage. We expect that with continued hydrological restoration (i.e., canal blocking), ET/P may increase and recommend that this data contributes to a long-term baseline from which restoration outcomes can be measured.