Forest fire induced impacts on phosphorus, nitrogen, and chlorophyll a concentrations in boreal subarctic lakes of northern Alberta

The biogeochemistry of 10 headwater lakes in burnt peatland-conifer catchments and 14 in unburnt catchments was evaluated throughout a summer 2 years following forest fire in a boreal subarctic region of northern Alberta. Cation exchange within burnt catchments resulted in proton flux and a 9% reduction in mean pH. Lakes in burnt catchments contained more than twofold higher (P << 0.01) mean concentrations of total, total dissolved, and soluble reactive phosphorus, 1.5-fold higher (P << 0.01) concentrations of dissolved organic carbon, and more than 1.2-fold higher (P < 0.05) concentrations of total and total dissolved nitrogen, nitrate + nitrite, and ammonium compared with reference lakes. Total phosphorus concentration explained 86% of the variance in reference lake chlorophyll concentration but was not related to chlorophyll concentration in burnt lakes. Analysis of chlorophyll - total phosphorus residuals suggested that algae in burn-impacted lakes were light limited. With the addition of five lakes burnt between 1961 and 1985, time since disturbance and percent disturbance combined explained 74% of the variance in total phosphorus among burnt lakes. Fire caused increased flux of materials to the study lakes with slow recovery over decades.