Red lakes are natural wonders, their vivid hues painting landscapes. These bodies of water are found across the globe. The science behind their coloration lies primarily in the biological activities of specialized microorganisms thriving in extreme environments. The spectacle of a red lake is a complex interplay of biology, chemistry, and environmental factors.
The Microorganisms Behind the Color
The striking red coloration of these lakes is predominantly due to microscopic life forms that have adapted to highly saline conditions. Two main types of microorganisms are responsible: halophilic archaea and certain types of salt-tolerant algae.
Halophilic archaea, such as Halobacterium salinarum, are single-celled organisms that thrive in environments with salt concentrations significantly higher than seawater, often optimally at 20-30% salinity. Alongside archaea, Dunaliella salina, a type of green microalgae, also contributes significantly to the red hue. This unicellular algae survives in hypersaline conditions like salt evaporation ponds. Their proliferation in such concentrated brines creates dense populations that tint the water with their distinctive pigments.
The Pigmentary Science
The colors observed in these lakes are produced by specific pigments within these microorganisms. The primary pigments involved are carotenoids, a group of organic compounds known for their colors. For instance, Dunaliella salina produces beta-carotene, the same pigment found in carrots. This beta-carotene masks the algae’s green chlorophyll, giving it a reddish-orange appearance, especially under conditions of high salinity and intense light.
Halophilic archaea, including Halobacterium salinarum, produce different carotenoid pigments, most notably bacterioruberin. These pigments are integrated into the cell membranes of the archaea. The production of these carotenoids serves a function for these microorganisms: protection against sunlight and ultraviolet (UV) radiation prevalent in their shallow, exposed habitats. By absorbing certain wavelengths of light and reflecting red light, these pigments give the water its characteristic red or pink coloration.
Environmental Conditions Shaping Redness
The red coloration of these lakes is linked to environmental conditions that favor the growth and pigment production of these microorganisms. High salinity is the primary factor, as the color-producing archaea and algae are halophiles. These organisms can tolerate salt concentrations often exceeding that of seawater, sometimes even approaching saturation. Without such high salt levels, these microorganisms would not dominate, and the lakes would not exhibit their red color.
High temperatures also play a significant role, as they accelerate evaporation, which in turn concentrates the salts in the lake water. This increased salt concentration further promotes the growth of halophilic organisms. Sunlight is another important factor, providing energy for Dunaliella salina’s photosynthesis and triggering protective pigment production in both algae and archaea. The combination of high salinity, elevated temperatures, and abundant sunlight creates a selective environment where these pigment-producing microorganisms flourish, leading to the red hues.
Global Occurrences and Ecological Role
Red lakes are found across various continents. Notable examples include Lake Hillier in Western Australia, attributed to Dunaliella salina and Salinibacter ruber bacteria. The Great Salt Lake in Utah also exhibits red sections, particularly its northern arm, due to Dunaliella salina algae and haloarchaea. In Bolivia, Laguna Colorada displays a red color primarily from red sediments and microorganisms like algae.
These extreme environments, despite their harsh conditions, support an adapted ecosystem. The microorganisms responsible for the red coloration, such as Dunaliella salina and halophilic archaea, serve as primary producers in these hypersaline ecosystems. They form the base of the food web, providing sustenance for other salt-tolerant organisms like brine shrimp. This ecological role highlights their importance in these challenging habitats.