DESERT POTHOLES: LIFE IN THE FAST POOL

An enigma of the Colorado Plateau high desert is the myriad of potholes, from shallow puddles to deeply carved pools. The existence of life in these harsh desert environments is largely controlled by the presence of collected rainwater. Despite the daily to seasonal extremes of widely fluctuating temperature, pH changes, and moisture-desiccation, organisms still adapt and flourish. The thriving prokaryotes and eukaryotes demonstrate the complex connections between life, water chemistry and geology.

Many species become dormant when potholes dry, and must endure intense heat, UV radiation, dessication and freezing, only to flourish again upon rehydration. A laboratory examination of dried biofilm from the potholes reveals that within 2 weeks of hydration, the surface of the desiccated, black biofilm became green from algal growth. During this time period, heterotrophic bacterial populations increased from 1.5 X 10⁵ cfu/cm² in the black, desiccated biofilms to 6.8 X 10⁶ cfu/cm², presumably due to support from primary production. Bacterial growth occurred as microcolonies, which likely helped protect them from the grazing protozoa. This complex biofilm may be responsible for dissolving the cement between the sandstone grains, allowing the potholes to enlarge, and also for sealing the potholes, enabling them to retain water longer than the surrounding sandstone.

The interactions between extreme conditions and cryptobiosis can provide analogs to early Earth environments and primitive biotic communities. These potholes provide the opportunity to examine the limiting boundary conditions for water and its effect on the development and evolution of life. Life in the fast pool holds great scientific value for understanding water-rock-biological interactions and adaptations to extreme environments. These analogs are critical for understanding how life could develop and exist on other planetary bodies such as Mars and Europa, or Earth-sized extrasolar planets.