Relationships between the biomass of algal crusts in fields and their compressive strength

In the desert areas of China investigated by the authors, various biological crusts were predominately associated with three blue-green algal (cyanobacterial) species, Microcoleus vaginatus Gom., Phormidium tenue (Menegh.) Gom. and Scytonema javanicum (Kütz.) Born et Flah. Their biomass and their compressive strength were measured simultaneously in the field in this study. It was also found that the compressive strength of algal crusts was enhanced with the increasing of algal biomass from an undetectable level to a value as high as 9.6 mg g−1 dry soil. However, when the algal biomass decreased, the compressive strength did not descend immediately, but remained relatively steady. The higher the algal biomass became, the thicker were the algal crusts formed. Given the same biomass, the highest compressive strength of man-made algal crusts in fields was found at an algal ratio of 62.5% M. vaginatus, 31.25% P. tenue and 6.25% S. javanicum, and it reached 0.89 kg cm−2. When the biomass of the crusts increased above the value of 8.16 mg chla g−1 dry soil, the compressive strength would not ascend easily. It indicated that the compressive strength of man-made algal crusts appeared temporarily saturated in the field.