Tropical peatlands play a critical role in regional water cycling, yet most tropical peat swamp forests (PSFs) are anthropogenically disturbed though 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 lacking. Here, therefore, we aimed to quantify rates of ET from a degraded tropical PSF in Central Kalimantan, in the context of broader peatland hydrology and site meteorology. From March to November 2020, ET ranged from 1.8–7.3 mm d -1, averaged 4.09 ± 0.06 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, if so, could potentially be used as an indicator for changing peatland condition over time.

Quantifying the hydrological connectivity of wetland ecosystems is crucial for their sustainable management. This study assessed the water balance of an Australian Sphagnum peatland via continuous monitoring of key hydrological parameters over four years (2017­–2021). Meteoric water inputs (rain and snow), evapotranspiration, changes in peat water storage (soil moisture and water table depth), groundwater contributions, and stream outflows were monitored or calculated over the four-year study period. Results showed a substantial groundwater contribution to the ecosystem, equivalent to 65% of total annual inputs. Groundwater inputs sustained stream outflows of 1.5 mm per day during periods without meteoric water input (i.e. summer dry periods), providing persistent surface wetness in this critical growing period. The continuous supply of groundwater to the peatland serves two important and interconnected environmental services. First, incoming groundwater enables the peatland water table to remain close to the surface, ensuring the persistence of the peatland vegetation during dry periods. Secondly, 94% of the peatland water balance (70% contributed from groundwater) leaves the peatland as streamflow, maintaining critical summer flows to downstream catchments. Climate change is predicted to increase the frequency and intensity of droughts in this region in the future, however, substantial groundwater contributions may provide more resilience to hydrologically intact peatlands in this region than what was previously thought.