Abstract:
Woody debris accumulations are important ecological components in low order
forested streams. They provide forage and refuge for a macroinvertebrates, which
are key trophic components for riverine fish. The occurrence of woody debris in
tropical streams is however threatened by large scale destruction of catchment
forests thereby threatening the riverine biodiversity. Despite their importance, the
current status of woody debris accumulations in tropical forested streams is
unknown. In this study we determined the densities of debris dams in a forested
stream section, their effectiveness in coarse particulate organic matter (CPOM)
retention and the associated macroinvertebrates along a 100m stream stretch
within the mid‐reaches of Sagana River. Volume of woody debris was estimated
from length, width and height. All components retained were collected, sorted and
dried to a constant weight at 85oC. Prior to drying of the organic matter,
macroinvertebrates in the CPOM were picked, sorted into different taxa and
enumerated. The average density over the whole study period was 2 woody debris
dam accumulations per 100m stream stretch. The macroinvertebrates occurring at
the debris dams were dominated by Coleoptera (47.3%), followed by Diptera
(22.7%) and Ephemeroptera (19.2%). The Coleoptera were dominated by Gyrinidae,
Elmidae and Scirtidae. Woody debris play an important role as long‐term retention
structures for organic matter and food resources. They forms an important
component of riverine ecosystems with regard to CPOM retention,
macroinvertebrates distribution and abundance which are indicators of habitat
condition. There is therefore need for re‐introductions of such structures for
effective channel restoration. We recommend maintenance of buffer strips of
riparian vegetation along river banks to protect riverine communities from adverse
effects of land‐use changes within Mt. Kenya catchment region.
