Impact of forest drainage on the macroinvertebrates of a small boreal headwater stream: Do buffer zones protect lotic biodiversity?

Abstract

Forest drainage, utilizing protective buffer zones, caused clear changes in the habitat structure as well as in the species richness and composition of moss-dwelling invertebrates in a small headwater stream. The aquatic moss Fontinalis dalecarlica was the dominant habitat in the control riffle areas, whereas sand dominated the riffles impacted by forest ditches. The significance of the forest ditches as a source of inorganic material was studied by comparing the quality of both indigenous and transplanted moss habitats. The Fontinalis tufts in the affected sites were silted up and contained a significantly higher average amount of inorganic matter than the mosses in the control site. The species richness of invertebrates within the silted mosses was significantly lower than at the control site. Shredder-feeding stoneflies dominated the moss communities of the control site, whereas Simuliidae dominated the impacted riffles. We suggest that the drainage-induced impoverishment of the benthic communities is due to two combined disturbance factors: (1) deposition of the particles on benthic habitats and (2) particle movement along the surfaces. Further, it is concluded that the present buffer zones and sedimentation ponds are insufficient to protect the biodiversity of streams draining easily eroding lands. In order to protect these vulnerable lotic ecosystems effectively, the most erodible parts of the catchment area should be undrained, and more retentive buffer mechanisms should be utilized in the drainage areas.