Lacul Negru (Ocna Sibiului)

Lacul Negru (Ocna Sibiului) is a salt lake located in Ocna Sibiului, Sibiu County, Transylvania, Romania. It is one of the many heliothermal lakes found in the Ocna Sibiului salt mine complex.

Characteristics:

Lacul Negru, meaning "Black Lake" in Romanian, derives its name from the dark appearance of its sediments and water. This coloration is due to the presence of organic matter and anaerobic bacteria that thrive in the lake's high salinity environment. The lake is known for its significant temperature gradient, a characteristic of heliothermal lakes. The surface water is typically cooler than the deeper layers, which can reach significantly higher temperatures due to the absorption of solar radiation.

Heliothermal Phenomenon:

The heliothermal effect in Lacul Negru is caused by the high concentration of salt in the water. This creates a density gradient, where the more saline water is denser and resides at the bottom, preventing convection currents that would normally distribute heat evenly. Consequently, solar radiation penetrates the upper layers of the lake and is absorbed by the bottom, warming the deeper water. This heat is trapped due to the density difference, leading to a significant temperature difference between the surface and bottom layers.

Therapeutic Properties:

Like other salt lakes in Ocna Sibiului, Lacul Negru is believed to possess therapeutic properties due to its high salinity and mineral content. The water is used for bathing and is thought to be beneficial for treating various conditions, including rheumatic diseases, skin conditions, and gynecological problems. The mud from the lake bottom is also used in therapeutic mud treatments.

Environmental Significance:

Lacul Negru, along with the other salt lakes of Ocna Sibiului, represents a unique and valuable ecosystem. These lakes support a specialized community of halophilic (salt-loving) organisms and are important for biodiversity. Conservation efforts are focused on protecting these sensitive environments from pollution and unsustainable tourism.