Short-term effects of wildfire on Patagonian headwater streams

In March-April 2015, the El Cristo fire burned 1228 ha of mixed Nothofagus forest in Los Alerces National Park (Argentine Patagonia). We compared physicochemical variables and community structure of burned and unburned headwater streams. Sampling began shortly after the fire was extinguished and comprised periodic water quality assessments and four visits to collect periphyton and invertebrate samples (May, August, October and December). Water temperature, total dissolved solids, total suspended solids and specific conductance were significantly higher in burned sites, whereas nutrient and oxygen concentrations exhibited no major differences. Chlorophyll a (used as a surrogate for autotrophic periphyton biomass) also did not differ significantly. Macroinvertebrate richness, abundance and diversity showed no differences across sites, but taxonomic composition and densities of sensitive taxa were markedly lower at burned streams. Oligochaetes and amphipods, however, were significantly more abundant in the disturbed reaches. Analysis of functional feeding groups revealed that the relative abundances of shredders and collector-filterers were lower at burned sites, possibly reflecting a shift in detrital input.