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

1. Macroinvertebrate production and macrophyte growth were studied in logged 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 been 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 stream was in the abundance of macrophytes. The combined biomass of Sparganium americanum and of Chara sp. was over 300-times greater in the logged than the unlogged section. 3. Annual macroinvertebrate production in the sediment was higher in the unlogged 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 logged 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 in the logged section, was 196 g m(-2) of stream bottom covered by this plant. 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 (41 g m(-2)). Sediments supported 99% of the annual production in the unlogged section, whereas macrophytes supported 76% in the logged section. 6. Much of the additional macroinvertebrate production in the logged section was by collector-filterers living on macrophytes. Production by collector-gatherers was also greater in the logged section, whereas production by other functional feeding groups changed little with logging. 7. Although logging along high-gradient, rocky streams also results in increased macroinvertebrate production, that increase often is stimulated by greater periphyton growth rather than the macrophyte growth observed in this low-gradient stream.