EFFECTS OF SELECTIVE LOGGING METHODS ON SUSPENDED SOLIDS CONCENTRATION AND TURBIDITY LEVEL IN STREAMWATER

Abstract

The impacts of 'conventional' and 'closely-supervised' selective logging methods on streamwater quality were studied in three small catchments in the Berembun Forest Reserve, Negri Sembilan, Peninsular Malaysia. The former method was typical of present commercial logging practices while in the latter, additional conservation measures were imposed and strictly adhered to during logging. Treatment effects were determined by comparing changes in the quality of streamwater in the logged catchments against an unlogged catchment during a three-year calibration period and a five-year post-treatment period. Before logging, streamwater was of clear quality during baseflow period but levels of . suspended solids and turbidity increased considerably during storm events. In the first year after conventional logging, annual means were 12 and 9 times those of the control catchment for suspended solids and turbidity respectively. These high levels persisted until the fifth year after logging. Another catchment where logging operations were closely-supervised showed only about two-fold increases for both suspended solids and turbidity levels; they recovered to the original levels within two years. Logging effects intensified during storm events with stormflow means in the first year after the conventional logging of 502 mg 1^-1 and 295 NTU for suspended solids and turbidity respectively, compared with 10 mg 1^-1 for suspended solids and 5.8 NTU for turbidity during baseflow period.