DOES LACUSTRINE TUFA REQUIRE A GROUND WATER SOURCE TO FLOURISH?

Tufa mounds and other forms of microbial carbonates are found in lake and river systems throughout the world. Notable modern and Pleistocene examples are found in the Western USA and Canada (Mono Lake, Big Soda Lake, Pyramid Lake, Lake Lahontan, Pavilion Lake), Australia (Yalgorup National Park (YNP) lakes, Coorong Lakes), SE Spain (Ruidera), Turkey (Lake Van, Lake Salda), and various lakes in Africa. Tufa mounds usually are located near the margins of lakes but can be rooted as deep as 60 m or more below the current lake level. Tufa can be precipitated as various forms of calcium carbonate (calcite, aragonite, monohydrocalcite, and ikaite) or magnesium carbonate (Mg-calcite, dolomite, and hydromagnesite). Ground water discharges to several lakes with tufa, such as Mono Lake, California, or Lake Clifton, Western Australia, are well documented. Ground water provides a necessary ion for precipitation that is not available in lake water. In YNP lakes and Big Soda Lake, Ca ions are provided by the ground water and in Lake Van, Mg ions are provided by ground water. In some cases, the morphology of the tufa mounds indicates unmistakable ground water inputs. For example, internal conduits that contain out flowing ground water occur in YNP lakes, Big Soda Lake, Lake Pavilion, and Mono Lake.

In arid regions, closed basin perennial lakes require ground water inputs to maintain their presence throughout the year, our data from the western US and Australia indicate that this ground water provides primary chemical components needed for tufa growth as well as nutrients that the microorganisms associated with tufa growth require to sustain their communities. Evidence to indicate that all tufa forms because of ground water inputs can not be demonstrated; however, data indicating that, particularly for arid zone topographically and/or hydrologically closed basins, ground water inputs are essential for developing large non-laminated mound-forming tufa.