Prescribed fire in Arizona chaparral: Effects on stream water quality

Abstract

Prescribed fire in Arizona chaparral can be used to obtain temporary improvements in forage supplies and a mosaic of uneven-aged stands of chaparral to reduce risks of widespread wildfires. A paired-watershed study demonstrated that prescribed fire had a negligible effect on the ionic composition of streamflow from a chaparral watershed that had been converted by means of a herbicide to grasses, forbs, and scattered shrubs. Before the prescribed fire, nitrate concentrations from the converted watershed were about 10 × greater than those from the control watershed because of nitrate release associated with the conversion process. The fire did not cause further increases in nitrate concentration. Concentrations of sulfrte, bicarbonate, and chloride anions and of calcium, magnesium, sodium, and potassium cations were not affected by the fire. Electrical conductivity and pH also were not influenced. Seasonal fluctuations in ionic concentrations coincided with seasonal variations in rainfall and streamflow. Nitrate concentrations increased during periods of high streamflow, but other anions and all cations decreased during periods of high flow. Electrical conductivity and pH remained relatively constant during the study.