Algae: An important agent in deposition of karstic travertines: Observations on natural-bridge Yerkopru travertines, Aladaglar, Eastern Taurids, Turkey

Travertines are terrestrial, fresh water carbonate deposits formed by karstic springs and associated streams which are supersaturated with respect to calcite. Field observations from recently travertine depositing karstic springs in the Aladaglar, Eastern Taurids - Turkey indicate that the deposition process is accelerated considerably by the physical and biochemical contribution of algae which mostly belong to classes of Cyanophyceae (blue-green algae), Chlorophyceae (green algae), Bacillariophyceae (diatoms), Euglenophyceae and Xantophyceae.Algae contributes physically to the deposition of travertine by means of trapping of inorganically formed calcite micro-crystals by algal filaments and mucilaginous secretions and by providing proper nucleation sites for calcite precipitation. Biochemical activity of algae also forces the aquatic system to deposit travertine due to the photosynthetic removal of free carbon dioxide from the solution. Field observations indicate that the rate of physical and chemical contribution to the deposition depends strongly on the hydraulic conditions. Physical and biochemical roles become important in high and low velocity/energy streams, respectively. The effect of algal association over the travertine deposition can be observed especially in streams where the ratio of algal mass to the rate of stream flow is high.Since climatic conditions have strong influence upon the abundance of algae, the rate of travertine deposited by algal contribution decreases during the winter months when the algal population decreases. Similarly, the biochemical contribution shows a diurnal pattern with a maximum during mid day because of the higher uptake of carbon dioxide via photosynthesis.