Characteristics of tufa algae community and bio-karstification at the Malinghe waterfall in Guizhou

Carbonates of the Triassic system，widely distributing in the Malinghe gorge，mainly form gorge，peak cluster，peak forest，stone forest landscapes. Among the geomorphologic landscape，there is a 2 km long gorge called the Tianxing gallery locating at 104°56′E and 25°08′N. The gallery has typical waterfall tufa that presents the appearance as vertical curtain，lobes and scaly. In order to investigate the role of flow interference and algae community during the development of the tufa at waterfall，the algae samples are collected at the fluid，inundation and moist regions from 3 waterfalls at the Tianxing gallery in August，2007. The morphological characteristics of tufa algal communities are recorded at field. The samples are divided into subsamples of algae and matrix which treated with 5 % C2H4O2 and 1 % HCl respectively. Then，the treated subsamples are analyzed qualitatively and quantitively after being mixed to each other. The micro-morphology samples of tufa are observed under the stereo microscope. The micro-deposit is separated from the sample and then added with a little 1 % HCl to observe the nucleus of micro-deposit. The results show that there are 5 algae coenotypes in the waterfall involving granular，lumps，mat，felty and pulverous. The dominant assemblage in the tufa algae is cyanophyta. In the moderate disturbed habitats by water flow，the species and community diversity are higher in the inundation region than other regions. Deposition and dissolution also take place in the tufa algae communities during the development of waterfall tufa，which may affect the direction of deposition and dissolution. The main role of tufa algae community is deposition under the condition of moderate disturbance by flow during the development of waterfall tufa，while under the conditions of stronger or weak disturbance of flow，the main role is dissolution. Therefore，it is considered that the synergism of flow disturbance degree and coenotype is one of the main factors that controlling the diversification in shape and structure of the waterfall tufa. And the moderate disturbance of flow is favorable for deposition of waterfall tufa.