Assessing leached TOC, nutrients and phenols from peatland soils after lab-simulated wildfires: Implications to source water protection

Pollutant leaching from wildfire-impacted peatland soils (peat) is well-known, but often underestimated when considering boreal ecosystem source water protection and when treating source waters to provide clean drinking water. Burning peat impacts its physical properties and chemical composition, yet the consequences of these transformations to source water quality through pollutant leaching has not been studied in detail. We combusted near-surface boreal peat under simulated peat smoldering conditions at two temperatures (250 °C and 300 °C) and quantified the concentrations of the leached carbon, nutrients and phenols from 5 g peat L^-1 reverse osmosis (RO) water suspensions over a 2-day leaching period. For the conditions studied, measured water quality parameters exceeded US surface water guidelines and even exceeded EU and Canadian wastewater/sewer discharge limits including chemical oxygen demand (COD) (125 mg/L), total nitrogen (TN) (15 mg/L), and total phosphorus (TP) (2 mg/L). Phenols were close to or higher than the suggested water supply standard established by US EPA (1 mg/L). Leached carbon, nitrogen and phosphorus mainly came from the organic fraction of peats. Heating peats to 250 °C promoted the leaching of carbon-related pollutants, whereas heating to 300 °C enhanced the leaching of nutrients. Post-heated peats leached higher loads of pollutants in water than pre-heated peats, suggesting that fire-damaged boreal peats may be a critical but underappreciated source of water pollution. A simplified Partial Least Squares (PLS) model based on other easily measured parameters provided a simple method for determining the extent of COD and phenolic pollution in bulk water, relevant for water and wastewater treatment plants. Conclusions from this lab study indicate the need for field measurements of aquatic pollutants downstream of peatland watersheds post-fire as well as increased monitoring and treatment of potable water sources for leachable micropollutants in fire-dominated forested peatlands.