Geoderma (Jul 2024)
Macro- and micronutrient release from ash and litter in permafrost-affected forest
Abstract
The impact of wildfire on terrestrial and aquatic ecosystems in permafrost-affected regions is a major and still poorly understood consequence of climate warming in high latitudes. Towards better characterization of processes controlling post-fire nutrient migration and to establish the relationship between forest litter and aquatic systems during a fire event, we studied organic and inorganic solute leaching from ash that was produced via burning organic litter (topsoil) collected in permafrost-affected forest in western Siberia. Litter samples were burned at 300, 450 and 600 °C and dissolved organic carbon (DOC), major elements (Ca, Mg, Cl, SO4, Na, N, P, K, Si), carboxylic organic acids, and ∼ 40 trace elements were analyzed in leachates (<0.45 µm and < 3 kDa) produced from ash reacting with water. The ashing temperature was one of the major factor controlling solute release to the aqueous solution, notably via its impact on leachate acidity and DOC concentration. The concentrations of DOC, organic (carboxylic acids) and inorganic nutrients, cationic metal micronutrients, and low-mobility geochemical tracers decreased with an increasing of ashing temperature. In contrast, labile anionic-group elements and alkaline metals were preferentially released at high ashing temperature. We also performed batch leaching of fresh (unburned) litter samples under identical experimental conditions. Results demonstrated that ash obtained from burning soil litter samples is less reactive than fresh litter. In particular, the majority of inorganic nutrients and carboxylic acids exhibited a factor of 3 to 10 higher mass-normalized yield to aqueous solution from fresh litter compared to that from ash. It follows that the fire severity is one of the main factors controlling organic and inorganic nutrient release from ash to soil and surface water. Results of the present study may help to foresee possible consequences of wildfire regime changes in permafrost regions on biogeochemical cycles of organic and inorganic macro- and micronutrients between the forest/tundra biomes and adjacent aquatic ecosystems.
