Development and application of hydrological and geomorphic diversity measures for mountain streams with check and slit-check dams

摘要

Habitat diversity is frequently used as an indicator of ecosystem health, but it is still difficult to find a parameter that can indicate river health. In this study, we suggest methods for calculating both hydrological and channel-geomorphic-unit diversity as factors that represent the health of a habitat. Both factors were computed based on a modified Shannon diversity index. The suggested methods for calculating the diversities were applied to ten reaches of two mountain streams with slit-check and check dams, because the influence of slit-check and check dams on fluvial systems can cause them to become either simpler or more dynamic. The usefulness and ecological significance of the methods were verified through correlation analysis using the species diversity of macroinvertebrates. Upstream reaches with check dams can appear to be reservoirs because of their slow velocity. Hydrological diversity, as the sum of the velocity and substrate diversities, is low for upstream reaches; the method also calculates the velocity and substrate diversities. Both the velocity and the substrate diversity showed significant correlation with species diversity, at 0.713 and 0.619, respectively. Channel geomorphic unit diversity (H'_(CGUD)) was highest at 1.80 for the upstream reach with a slit-check dam, while the diversity of the check dam was 1.05. The diversity index is improved by geomorphic unit change after dam slit construction, which reveals that the index is sensitive to changes. These parameters, namely, velocity, substrate and channel geomorphic unit diversity, are useful non-biological indicators for easily assessing river ecosystems. Channel-geomorphic-unit diversity is a particularly sensitive indicator for calculating and distinguishing various types of streams, and therefore, it can be useful for monitoring temporal changes at the reach scale.