Biomass burning drives atmospheric nutrient redistribution within forested peatlands in Borneo

Abstract

Biomass burning plays a critical role not only in atmospheric emissions, but also in the deposition and redistribution of biologically important nutrients within tropical landscapes. We quantified the influence of fire on biogeochemical fluxes of nitrogen (N), phosphorus (P), and sulfur (S) in a 12 ha forested peatland in West Kalimantan, Indonesia. Total (inorganic + organic) N, \({{{\rm{NO}}}_{3}}^{-}\) –N, \({{{\rm{NH}}}_{4}}^{+}\) –N, total P, \({{{\rm{PO}}}_{4}}^{3-}\) –P, and \({{{\rm{SO}}}_{4}}^{2-}\) –S fluxes were measured in throughfall and bulk rainfall weekly from July 2013 to September 2014. To identify fire events, we used concentrations of particulate matter (PM₁₀) and MODIS Active Fire Product counts within 20 and 100 km radius buffers surrounding the site. Dominant sources of throughfall nutrient deposition were explored using cluster and back-trajectory analysis. Our findings show that this Bornean peatland receives some of the highest P (7.9 kg \({{{\rm{PO}}}_{4}}^{3-}\) –P ha⁻¹yr⁻¹) and S (42 kg \({{{\rm{SO}}}_{4}}^{2-}\) –S ha⁻¹yr⁻¹) deposition reported globally, and that N deposition (8.7 kg inorganic N ha⁻¹yr⁻¹) exceeds critical load limits suggested for tropical forests. Six major dry periods and associated fire events occurred during the study. Seventy-eight percent of fires within 20 km and 40% within 100 km of the site were detected within oil palm plantation leases (industrial agriculture) on peatlands. These fires had a disproportionate impact on below-canopy nutrient fluxes. Post-fire throughfall events contributed >30% of the total inorganic N (\({{{\rm{NO}}}_{3}}^{-}\) –N + \({{{\rm{NH}}}_{4}}^{+}\) –N) and \({{{\rm{PO}}}_{4}}^{3-}\) –P flux to peatland soils during the study period. Our results indicate that biomass burning associated with agricultural peat fires is a major source of N, P, and S in throughfall and could rival industrial pollution as an input to these systems during major fire years. Given the sheer magnitude of fluxes reported here, fire-related redistribution of nutrients may have significant fertilizing or acidifying effects on a diversity of nutrient-limited ecosystems.