Effects of logging on macroinvertebrate production in a sand-bottomed, low-gradient stream

1. Macroinvertebrate production and macrophyte growth were studied in logge d and unlogged sections of a sand-bottomed, low-gradient, blackwater stream on the Coastal Plain of Virginia, U.S.A. A section of the catchment had be en clear-cut 3 years prior to sampling. No logging occurred in the upstream area of the catchment, which had experienced almost no land disturbance by humans for over 100 years. 2. A primary difference among the logged and unlogged sections of the strea m was in the abundance of macrophytes. The combined biomass of Sparganium a mericanum and of Chara sp. was over 300-times greater in the logged than th e unlogged section. 3. Annual macroinvertebrate production in the sediment was higher in the un logged section (41 g dry mass m(-2)) than in the logged section (25 g m(-2) ). 4. Annual macroinvertebrate production on Sparganium was higher in the logg ed section (10 g m(-2) of plant surface area) than in the unlogged section (6 g m(-2)). Annual production associated with Chara, which occurred only i n the logged section, was 196 g m(-2) of stream bottom covered by this plan t. 5. Whole-stream annual macroinvertebrate production, calculated by summing habitat-specific production that was weighted by habitat availability, was greater in the logged section (103 g m(-2)) than in the unlogged section (4 1 g m(-2)). Sediments supported 99% of the annual production in the unlogge d section, whereas macrophytes supported 76% in the logged section. 6. Much of the additional macroinvertebrate production in the logged sectio n was by collector-filterers living on macrophytes. Production by collector -gatherers was also greater in the logged section, whereas production by ot her functional feeding groups changed little with logging. 7. Although logging along high-gradient, rocky streams also results in incr eased macroinvertebrate production, that increase often is stimulated by gr eater periphyton growth rather than the macrophyte growth observed in this low-gradient stream.