Fire and water: fire impacts on physicochemical properties of freshwater ecosystems

Freshwater ecosystems are intensely endangered, entailing declines in the biodiversity and ecosystem services. Fire may affect the physicochemical water quality parameters of these environments by transference of ash and toxic substances into water bodies, altering nutrient and oxygen concentrations, temperature or turbidity. However, major knowledge gaps in the impacts of fire on freshwater habitats are prevalent. We conducted a systematic review by searching articles in the Web of Science related to the impacts of fire on the physicochemical water properties of freshwater ecosystems. We quantified the set of physicochemical parameters investigated and provided an overview of fire-mediated alterations. We found 54 articles published between 1976 and 2019, with a significant increase during the last decade. Research was strongly biased towards a few temperate western countries, mostly across North America, Europe and Australia. Lotic systems were considerably more studied than lentic systems. Overall, 57 chemical and 17 physical parameters were evaluated, comprising 304 and 77 cases, respectively. Fire altered 68 % of the cases studied and contingency tables showed that this alteration was proportionally similar between chemical (66 %) and physical (75 %) properties. Nutrient concentration, metal ions, alkalinity, turbidity and temperature were parameters recurrently increased by fire (56 %), whereas oxygen mostly decreased (70 %). Our study demonstrates that fire commonly affects water quality parameters of freshwater ecosystems. Biases and resulting gaps may steer future sampling efforts and promote a broader understanding of the impacts of fire on these environments. Our results may ultimately guide applicable conservation policies for biodiversity and water management strategies of freshwater ecosystems.