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

Abstract

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.