Nutrient loss from disturbed forest watersheds in Oregon's coast range

Abstract

Dissolved nutrients were monitored bi-weekly in stream water draining 14 upland watersheds in Oregon's Coast Range after spraying with 2,4,5-T + 2,4-D, clearcut harvesting and slash burning. Anion generation and leaching were primarily studied. The nitrate concentrations fell and the bicarbonate concentrations rose during summer low-flows from treated watersheds without detectable increases in loss of macronutrients (N, Ca, Mg, K, Na). The stream water concentrations of bicarbonate (the most prevalent anion) related to watershed orientation and the degree of devegetation. Nitrate concentrations appeared to be correlated positively with watershed drainage rates. Studies with incubated soils and field sampling of soil solution indicate that denitrification probably minimizes nitrate loss from saturated soils during frequent winter to spring storm periods.