Abstract

A step-pool system is a geomorphologic phenomenon with alternating steps and pools having a stair-like appearance. The ecological and hydraulic features of step-pool systems are studied by field investigation, sampling, and analysis. Field investigations are done on the Jiuzhai and Shengou Creeks, where large scale step-pool and regular step-pool systems have developed, and the Jinsha River and Jiangjia and Xiaobaini Ravines. Boulders, cobbles, and gravel tightly interlock and form the steps having an inherent stability which only extreme floods are likely to disturb. Sand, silt, and clay deposit in the pools behind the steps. These steps and pools provide high diversity of habitat for the stream bio-community. The density of benthic macro-invertebrates in the streams with step-pool systems is 800 times higher than neighboring streams without step-pool systems. A new habitat diversity index is proposed considering the spacial distribution of various substrates, velocity, and water depth. The study reveals that the diversity of benthic macro-invertebrates increases with the habitat diversity following a logarithmic law.

Keywords: Step-pool system, Benthic macro-invertebrates, Biodiversity, Habitat diversity, Riverbed inertia, Stream stability