In October of 2017 a series of rural fires affected Portugal’s Central Region, leading to the destruction of 40–60% of the forest area in some districts. A monitoring program was initiated in 5 catchments of the Mondego drainage basin, in order to understand the temporal evolution of the water’s physical and chemical characteristics in a post-fire scenario. This monitoring program was implemented in catchments with sizes between 20 km2 and 160 km2 in areas 60%–99% burnt. For each catchment a gauging point was selected near the mouth of the river. These 5 gauging points were assessed monthly, starting one month after the fire, in November 2017, and ending in June 2018. In each campaign stream water was sampled for laboratory analysis and in-situ physical-chemical proprieties were measured. Major ions in water samples were determined through ion chromatography (IC) and molecular absorption spectroscopy, and inductively coupled plasma optical emission spectrometry (ICP-OES). Trace elements were evaluated through ICP-OES and inductively coupled plasma mass spectrometry. Total organic carbon and dissolved organic carbon were evaluated through the oxidation method and polycyclic aromatic hydrocarbons were determined by high-performance liquid chromatography. The data collected was crossed with the catchment’s morphometric, geological and land use data, including characteristics of the burnt area.

Results showed that these fires affected the surface waters in the studied catchments, producing an increase in turbidity, and in the concentrations of Al, Fe, Mn and possibly NO 3 and As.