西南山区河流阶梯—深潭系统的生态学作用

A Study of the Ecological Functions of Step-pool System in Southwest Mountain Streams

山区河流发育的阶梯—深潭系统具有显著的生态学作用。阶梯—深潭系统增大水流阻力和河床抗冲刷力,稳定了河床和岸坡。大卵石堆积成阶梯,细颗粒泥沙在深潭河段的缓流滞流区沉积下来形成淤泥层,形成适宜多种生物的栖息地。选择小江支流———深沟、蒋家沟和小白泥沟,以及四川九寨沟和金沙江进行野外实验、取样分析。结果发现阶梯—深潭系统较发育的深沟和九寨沟底栖动物密度高达552个/m2,生物量高达5.96 g/m2。而邻近的小白泥沟和蒋家沟底栖动物密度仅0.75个/m2,生物量不到0.006 g/m2。考虑河流不同部位底质、水深、流速等特性,提出了生物栖息地多样性及其计算方法,研究发现大型无脊椎动物的生物多样性随栖息地多样性增加而增加。利用阶梯—深潭系统治理山区河流,既能保持河道稳定,又能维持较高的生物多样性,保持健康的河流生态系统。

The development of step-pool system plays an important role in stream ecology. Step-pool system maximizes the flow resistance and protects the bed sediment from erosion. Thus the riverbed and bank slope are stabilized. Boulders, cobbles and gravel tightly interlock and form the steps having an inherent stability which only extreme floods are likely to disturb. Silt and clay deposit in the pools behind the steps. These steps and pools provide high diversity of habitats for stream bio-community. Field investigations are performed to the Xiaojiang River, Jinsha River and Jiuzhai Creek. Step-pool systems develop well in the Jiuzhai Creek and Shengou Ravine, which is a tributary of the Xiaojiang River. The density of benthic macro-invertebrate is 552/m^2 in the Jiuzhai Creek and 398/ m^2 in the Shengou Ravine and the density of bio-mass of benthic macro-invertebrate is 4.75g/m^2 in the Jiuzhai Creek and 5.96 g/m^2 in the Shengou Ravine. As a comparison, the density of benthic macro-invertebrate is only 0.75/m^2 in the Jiangjia Ravine and 0 in the Xiaobaini Ravine, which are Mso the tributary of the Xiaojiang River, but no step-pool develops in the ravines. The density of bio-mass of benthic macro-invertebrate is only 0.006 g/m^2 in the Jiangjia Ravine and 0 g/m^2 in the Xiaobaini Ravine. This paper proposes the concept of habitat diversity and a calculation formula considering the spaciousdistribution of various substrates, velocity and water depth. The study reveals that the biodiversity of benthic macro-invertebrates increases with the habitat diversity in a logarithmic law. Artificial step-pool system can be used for training of mountain streams, which may stabilize the streambed and bank slope, restore healthy river ecology and high biodiversity, and better aesthetic landscape as well.