Physical, chemical, and biological impacts of intensive forest management on streams draining watersheds in the coastal plain of Alabama

Five watersheds drained by first-order streams and containing timber that was 80+ years old were selected to study the impacts of clearcutting and planting site preparation on water quality in the presence and absence of streamside management zones (SMZs). One watershed was maintained as a reference with no treatment while the remaining 4 were clear cut harvested. Two of the harvested watersheds were clearcut to the stream banks and two maintained 10 m SMZs on each side of the stream. Site preparation included mechanical (shearing, root-raking and windrowing) or chemical, each in the presence and absence of SMZs. Chemical site preparation was accomplished by the aerial application of a mixture of imazapyr plus glyphosate (1.12 plus 3.36 kg ai/ha). Water temperature, sediment yield, periphyton biomass, macroinvertebrate population dynamics, and herbicide off-site movement into streams were measured and differences identified as a function of the treatments versus the reference channel using Randomized Intervention Analysis (RIA). RIA identified differences in water quality among the various treatments at all stages (i.e. harvest and site preparation) of the study. In general, mechanical site preparation resulted in greater impacts on the physical, chemical and biological aspects of water quality than chemical site preparation.