In 2012, Credit Valley Conservation inventory staff discovered a provincially and nationally rare phenomenon along the Niagara Escarpment at Silver Creek and Belfountain. This discovery was of tufa, a soft rock, being actively formed at the emergence of select springs. Tufa is a variety of limestone. It differs from typical Escarpment rock formed on ancient sea beds from calcium-rich shells, exoskeletons and coral. Instead, tufa is formed by calcium precipitated out of water. Bits of the precipitated calcium carbonate can amalgamate to create larger rocks.
Ontario’s known tufa deposits are formed at springs and waterfalls, particularly along the Niagara Escarpment. Tufa is only known in Ontario from Brantford, Paris, Dundas, Niagara Falls, and with the discoveries reported herein, Silver Creek and Belfountain. In 2008, the Ontario Ministry of Natural Resources designated a tufa deposit in Brantford as a provincially significant Earth Science Area of Natural and Scientific Interest.
Tufa only forms at springs where just the right conditions exist. First, ground water must contain carbon dioxide picked up from the air, making the water weakly acidic. Second, the ground water must become supersaturated with soluble calcium by dissolving limestone. Third, as the calcium-rich water emerges from the ground, it must release enough carbon dioxide to cause the soluble calcium to solidify into insoluble calcium (rock). The same precipitation process is responsible for the formation of stalactites and stalagmites in caves.
Tufa was first found in the Credit River watershed by the author and assistant Pete Davis at Silver Creek Conservation Area. The author recognized it based on tufa deposits seen on a Hamilton Naturalist’s Club hike to Spencer’s Gorge (Dundas) led by Dr. Terry Carleton, a forestry professor at the University of Toronto. Dr. Carleton was the first to document tufa deposits at Spencer’s Gorge, which he recognized based on his observations of similar occurrences in England. News of the discovery at Silver Creek led to CVC’s Scott Sampson reporting possible tufa at Belfountain Conservation Area. A visit by the author, CVC’s Dawn Renfrew, biologist Lynda Ruegg, and Dr. Carleton confirmed the report.
Tufa deposits at Belfountain may be more abundant than anywhere else in Ontario. Tufa deposits can be easily observed at this conservation area on north-facing slopes. The best viewing spot is from the foot bridge that spans the West Credit River. The largest and most impressive tufa deposit can be seen from here on the slope on the south side of the river. This tufa deposit is almost completely covered by a blanket of moss in shades of green and red, with a small patch of whitish tufa peeking through.
Tufa deposits are a challenging growth environment for plants because soil is absent, the substrate is rock, conditions are calcareous, and there is a constant flow of cold water. Few plants can function in such environments; many of those that can are mosses, especially those specializing in seepy, calcareous habitat. Our tufa deposits, if not barren, tend to be either dominated by mosses, or populated by hardy plants such as Watercress (Nasturtium sp.), Jewelweed (Impatiens sp.) and European Coltsfoot (Tussilago farfara). The dominant moss on Silver Creek and Belfountain tufa deposits is Cratoneuron filicinum. It is not a rare moss, however, there are some provincially rare mosses known to grow on tufa that could be found in future inventories. Interestingly, because photosynthetic activity removes carbon dioxide from the spring water, mosses and other plants actually help create more rock once they become established.
In addition to potentially supporting rare mosses, tufa formation areas may also act as amphibian and dragonfly/damselfly breeding habitat. This is because tufa is often formed on slopes, creating terraces on which small pools of water are formed. Evidence suggests that salamanders (some of which are Species At Risk) may breed in these pools, and as some dragonfly/damselfly species restrict their breeding areas to seeps, they may also be found in these tufa pools. These spring-fed pools may also be an important water source for wildlife, especially if they remain unfrozen in winter months.
Tufa formation is a topic only recently receiving attention amongst biologists, and with increased awareness, the author expects more tufa deposits to be found in the future along the Niagara Escarpment.
Leanne Wallis
Credit Valley Conservation
