Abstract: | In January 1979 four experimental catchments in forests of southeastern New South Wales were burnt by wildfire. Logging before the fire had no detectable effect on concentrations of Ca, K, Mg, Na, Cl, NO3, nor on pH of stream waters. In all burnt catchments mean K concentrations increased by from 20 per cent to 60 per cent for a 12 month period and nitrate concentrations increased by factors of about ten in severely burnt catchments. In one of the catchments (unlogged) Ca also increased. From one year to four years after the fire, concentrations of all ions were either close to or less than levels predicted from the control but, during the fifth and sixth years, concentrations of Mg and Na were higher by 20 per cent to 60 per cent. In all burnt catchments, cation exports increased considerably during the first three years after the fire but major components of these increases were elevated levels of runoff. Exports of Mg and Na were higher than those of the control during the fifth and sixth years after the fire, although runoff had returned to pre-fire levels in the two unlogged catchments and was 10 per cent to 20 per cent greater than the control in the two logged catchments. During this final period, increased ion concentrations were the main factors which contributed to the elevated exports. Post-fire logging in one catchment had no detectable effects on streamwater parameters measured in the study but was associated with a further increase in runoff. |