Nitrate formation and movement before and after clear-cutting of a monitored watershed in central New Brunswick, Canada
A watershed of 391 ha, supporting tolerant hardwoods on elevated sloping portions and softwoods on low lying areas, was clear-cut in 1978. Nitrate nitrogen was monitored over 5 years before and 3 years after clear-cutting by periodic extraction of soil solution samples and continuous sampling of the brooks draining the cut and a similar control watershed. The brooks were gauged to determine water discharge. Before clear-cutting, nitrate nitrogen was not detectable for most of the time in soil solutions under softwood cover, but occurred commonly under hardwood cover with concentrations ranging upward to 4.7 mg/L. Nitrate nitrogen in the brooks varied from undetectable to 0.3 mg/L. After clear-cutting, nitrate nitrogen increased to maximum concentrations of 13.4 mg/L, in the soil solution under hardwood cover, and 1.6 mg/L, in the main channel of the brook. Soil solution nitrogen was not changed significantly by clear-cutting of softwood stands. The 3-year cumulative nitrogen loss attributable to clear-cutting was 19.1 kg/ha. Nitrate nitrogen in soil solutions, branch, and main stream indicated that disproportionately larger amounts of nitrogen were lost from the elevated and sloping portions of the watershed than from the lower lying areas.