Effects of water transfer on aquatic insects in a stream in Hong Kong

摘要: Hong Kong streams serve as indirect catchments for storage reservoirs to which they are connected by a network of undergound tunnels. Water transfer reduces stream flow downstream the extraction point, and surface flows may disappear in affected reaches during dry season. The ecological effects periodic dewatering on aquatic insects were investigated Tai Po Kau Forest Stream, Kong, where water at weir gives rise intermittent immediately well studied perennial section. Benthic samples taken from reach 48 occasions over two year period encompassing seasons. Trends total population densities unclear, with considerable fluctuations study period. In contrast, species richness declined markedly after disappeared, reaching lowest values end both A rapid increase accompanied resumption onset summer monsoon, maximum wet season up five times greater than Dry declines Ephemeroptera Trichoptera dramatic Coleoptera (Elmidae especially Helodidae). situation was reversed when (especially Cheumatopsyche Chimarra) (Leptophlebiidae, Baetidae Heptageniidae) numerous. Community structure recovered quickly disturbance, due largely recolonization drifting animals. At scale investigated, community resilient disturbance because source mobile colonists available upstream. However, if affects far downstream, presence suitable upstream cannot be guaranteed, recovery will delayed. Lowland often polluted host exotic species; such circumstances transfers exacerbated is hindered.