Ecosystems

Thermal Spring Ecosystems

Thermal springs are extremely unique and fragile ecosystems with rare micro-climatic conditions created by and wholly dependent upon geothermal activity. The chemicals and minerals dissolved in the water and the associated cycles create a biologically harsh environment. Only a small group of plants and animals can withstand these conditions and they have to be uniquely adapted to be able to survive. They are also very sensitive to disturbance.

In 1928 an early thermal spring biologist Charles T. Brues described the many problems in trying to protect the natural contingent of flora and fauna that is the biodiversity of these unique ecosystems:

“From the naturalist’s standpoint and from that of the nature-lover as well it is distressing to record that all except the most inaccessible springs, or those included within the boundaries of National Parks, have been either converted to natatoria, sanatoria for arthritics, radium baths and the like, or have been diverted into irrigation ditches, sometimes with the aid of dynamite, to supply a few desolate ranches with water for cattle and alfalfa. For this reason the fauna and the flora of these thermal springs is destined soon to be wiped out over considerable areas by the advance of commercialism.”

Interestingly, this was stated two years after the Banff Springs Snail became known to science.

All the thermal springs on Sulphur Mountain, even though they are within a national park or national historic site, have been modified by development to varying degrees. Some have returned to more natural states, whereas others continue to be highly regulated.

A series of virtual models have been made to help better understand how Banff’s thermal spring ecosystems operate. A most basic model for a typical Sulphur Mountain thermal spring shows water from rain and snow seeping into the earth to a depth of 2.5 to 3.2 km through cracks in the rock. The water becomes heated by the earth’s thermal gradient and pressurized. When it reaches the Sulphur Mountain Thrust Fault, it flows back to the surface. Seasonal changes due to frozen ground and no recharge during the winter and resumption of recharge with the spring thaw, result in seasonal changes in flow rates, water temperatures, and dissolved chemicals.

Simplified model of how Sulphur Mountain thermal springs work.

Simplified model of how Sulphur Mountain thermal springs work.

A large component of each thermal spring ecosystem is found underground. As the water passes through the rocks and becomes heated, gasses and minerals dissolve from the rocks and become suspended in the water. A subterranean bacterial community consumes and changes these dissolved materials. Sulfate reducing bacteria (including Desulfovibrio, Clostridium, and the strict anaerobe Desulfotomaculum) can strip the oxygen from sulphate (SO4) for use in metabolic processes and create hydrogen sulphide (that rotten egg smell).

When the water reaches the surface in the origin pools of the thermal springs, it sustains another microbial community that in turn uses and converts the gasses and dissolved minerals. For example, the colourless, filamentous bacterium Beggiatoa, the white filamentous Thiothrix, the colony-forming Thiobacteria thiooxidans, and the purple bacteria can oxidize hydrogen sulphide to create elemental sulphur. Organic material such as leaves and woody debris (twigs, sticks, and logs) can contribute nutrients and structure to the biotic community within the spring’s origin.

Given sufficient oxygen and light, algae can grow and flourish. Water then flows out of the spring origin pool into the outflow stream. Both abiotic and biotic gradients are created as various biogeochemical constituents such as dissolved oxygen, hydrogen sulphide, carbon dioxide and water temperature change as the water flows downstream.

And of course, overlaying these dynamic interactions are seasonal changes that occur within the various components of the thermal spring ecosystem.

A simple model of a thermal spring ecosystem.

A simple model of a thermal spring ecosystem.

Another thing that happens once the water reaches the surface is that tufa (“TOO-fuh”), a type of soft rock, is formed. When thermal spring water that has been heated, pressurized, and laden with minerals bursts onto the surface, it releases dissolved carbon dioxide. This reduces the ability of the water to hold the dissolved calcium and magnesium it has gathered by flowing through carbonate rocks such as limestone and dolomite. As a result, tiny crystals of calcite and gypsum grow. Some species of mosses actually help the process of tufa formation, as does the agitation of the flowing water. This is the youngest rock in the Canadian Rockies.

Just think! The youngest rocks are being formed before your very eyes from other rock that is millions of years old.

Tufa, the youngest rock in the Canadian Rockies, is being formed along the wall of the Cave at the Cave and Basin National Historic Site, by thermal spring water.

Tufa, the youngest rock in the Canadian Rockies, is being formed along the wall of the Cave at the Cave and Basin National Historic Site, by thermal spring water.

Next Page – Seasonal Changes near Banff’s Thermal Springs