Tropical peatlands are among the most carbon‐dense ecosystems on Earth, and their water storage dynamics strongly control these carbon stocks. The hydrological functioning of tropical peatlands differs from that of northern peatlands, which has not yet been accounted for in global land surface models (LSMs). Here, we integrated tropical peat‐specific hydrology modules into a global LSM for the first time, by utilizing the peatland‐specific model structure adaptation (PEATCLSM) of the NASA Catchment Land Surface Model (CLSM). We developed literature‐based parameter sets for natural (PEATCLSM_Trop,Nat) and drained (PEATCLSM_Trop,Drain) tropical peatlands. Simulations with PEATCLSM_Trop,Nat were compared against those with the default CLSM version and the northern version of PEATCLSM (PEATCLSM_North,Nat) with tropical vegetation input. All simulations were forced with global meteorological reanalysis input data for the major tropical peatland regions in Central and South America, the Congo Basin, and Southeast Asia. The evaluation against a unique and extensive data set of in situ water level and eddy covariance‐derived evapotranspiration showed an overall improvement in bias and correlation compared to the default CLSM version. Over Southeast Asia, an additional simulation with PEATCLSM_Trop,Drain was run to address the large fraction of drained tropical peatlands in this region. PEATCLSM_Trop,Drain outperformed CLSM, PEATCLSM_North,Nat, and PEATCLSM_Trop,Nat over drained sites. Despite the overall improvements of PEATCLSM_Trop,Nat over CLSM, there are strong differences in performance between the three study regions. We attribute these performance differences to regional differences in accuracy of meteorological forcing data, and differences in peatland hydrologic response that are not yet captured by our model.

Tropical biogenic sources are a likely cause of the recent increase in global atmospheric methane concentration. To improve our understanding of tropical methane sources, we used the eddy covariance technique to measure CH₄ flux (F_CH4) between a tropical peat forest ecosystem and the atmosphere in Malaysian Borneo over a 2‐month period during the wet season. Mean daily F_CH4 during the measurement period, on the order of 0.024 g C‐CH₄·m⁻²·day⁻¹, was similar to eddy covariance F_CH4 measurements from tropical rice agroecosystems and boreal fen ecosystems. A linear modeling analysis demonstrated that air temperature (T_air) was critical for modeling F_CH4 before the water table breached the surface and that water table alone explained some 20% of observed F_CH4 variability once standing water emerged. Future research should measure F_CH4 on an annual basis from multiple tropical ecosystems to better constrain tropical biogenic methane sources.

(1) Background: Nitrogen (N) fertilization on drained tropical peatland will likely stimulate peat decomposition and mineralization, enhancing N₂O emission from the peat soil. (2) Methods: A field experiment was conducted to quantify the N₂O emissions from soil in an oil palm plantation (Elaeis guineensis Jacq.) located in a tropical peatland in Sarawak, Malaysia, under different rates of N fertilizers. The study was conducted from January 2010 to December 2013 and resumed from January 2016 to December 2017. Nitrous oxide (N₂O) flux was measured every month using a closed chamber method for four different N rates; control—without N (T1), 31.1 kg N ha⁻¹ yr⁻¹ (T2), 62.2 kg N ha⁻¹ yr⁻¹ (T3), and 124.3 kg N ha⁻¹ yr⁻¹ (T4); (3) Results: Application of the N fertilizer significantly increased annual cumulative N₂O emissions for T4 only in the years 2010 (p = 0.017), 2011 (p = 0.012), 2012 (p = 0.007), and 2016 (p = 0.048). The highest average annual cumulative N₂O emissions were recorded for T4 (41.5 ± 28.7 kg N ha⁻¹ yr⁻¹), followed by T3 (35.1 ± 25.7 kg N ha⁻¹ yr⁻¹), T1 (25.2 ± 17.8 kg N ha⁻¹ yr⁻¹), and T2 (25.1 ± 15.4 kg N ha⁻¹ yr⁻¹), indicating that the N rates of 62.2 kg N ha⁻¹ yr⁻¹ and 124.3 kg N ha⁻¹ yr⁻¹ increased the average annual cumulative N₂O emissions by 39% and 65%, respectively, as compared to the control. The N fertilization had no significant effect on annual oil palm yield (p = 0.994). Alternating between low (deeper than −60 cm) and high groundwater level (GWL) (shallower than −60 cm) enhanced nitrification during low GWL, further supplying NO₃⁻ for denitrification in the high GWL, and contributing to higher N₂O emissions in high GWL. The emissions of N₂O ranged from 17 µg N m⁻² hr⁻¹ to 2447 µg N m⁻² hr⁻¹ and decreased when the water-filled pore space (WFPS) was between 70% and 96%, suggesting the occurrence of complete denitrification. A positive correlation between N₂O emissions and NO₃⁻ at 70–96% WFPS indicated that denitrification increased with increased NO₃⁻ availability. Based on their standardized regression coefficients, the effect of GWL on N₂O emissions increased with increased N rate (p < 0.001). Furthermore, it was found that annual oil palm yields negatively correlated with annual N₂O emission and NO₃⁻ for all treatments. Both nitrification and denitrification increased with increased N availability, making both processes important sources of N₂O in oil palm cultivation on tropical peatland.; and (4) Conclusions: To improve understanding of N₂O mitigation strategies, further studies should consider plant N uptake on N₂O emissions, at least until the completion of the planting.