How much external noise can you add to a wetland environment before the wildlife inhabitants really start to suffer?
Relatively little scientific research appears to have been conducted on this subject. Yet an understanding of cumulative noise pollution is essential to properly assessing the long-term impact of the proposed St. Marys Cement under-the-lake mine south of Bowmanville.
A recently published research paper found biochemical markers of increased stress levels, as well as reduced hatching success, among birds chronically exposed to industrial noise. We’ll get to that paper below, but first, here’s a refresher on the setting for the mine proposal.
The St. Marys mine proposal (official Project Description here) describes a mine-entrance tunnel near the bottom of the existing limestone quarry on the Lake Ontario shoreline. The tunnel will lead to under-the-lake caverns, which will be excavated over a 100-year period.
The project site is adjacent to two Provincially Significant Wetlands, Westside Marsh and Bowmanville Marsh. These wetlands are among the remnants of what was once a very extensive array of coastal wetlands all around Lake Ontario. The remaining coastal wetlands are still of key importance to resident and migratory bird populations and to many freshwater fish species who depend on the wetlands at some stage of their life-cycles.
If the project is approved as proposed, 4 million tonnes of limestone will be blasted and hauled out from these caverns each year. The operation will require ventilation fans moving fresh air into the mine and exhaust air back out, to enable work to be conducted throughout a network of chambers that will eventually extend approximately 14 square kilometers under the lake.
Mining trucks will carry the limestone out of the mine and into the quarry, where it will be crushed into aggregate suitable for construction use. Then approximately 500 truckloads per day (based on seven days/week haulage) will leave the St. Marys site carrying aggregate to the primary market on the east side of the Greater Toronto Area.
The environmental viability of the project must be assessed by looking at the cumulative effects. The blasting, drilling, ventilation fans, trucks and crushers will add noise to an environment that is already anything but quiet.
At present both Westside Marsh and Bowmanville Marsh are subject to significant anthropogenic noise levels on a 24-hour basis. The operations of St. Marys are just one component of that noise.
Noise from St. Marys existing operations comes from blasting and hauling limestone immediately to the west of Westside Marsh, trucking of cement products, and major excavation and berm-building directly north of Westside Marsh.
Another constant noise source is Highway 401, just to the north. At present the traffic noise consists of a constant loud hum, punctuated by accelerating trucks, motorcycles, and sirens. The St. Marys mine would add to that traffic noise, as 500 or more additional trucks come and go every day. (The route in and out of the St. Marys property, and on and off the 401, are shown in yellow on the above map.)
One of the busiest rail lines in Canada passes directly north of the quarry, about 500 meters north of Westside Marsh, and through the north end of Bowmanville Marsh.
Noise and stress in bird populations
A recent paper published in the Proceedings of the National Academy of Sciences (US) notes that noise pollution “alters habitats, degrades natural acoustic conditions, and partially or fully excludes species that are sensitive to noise exposure from affected areas.”1
Among the species that remain in noise-affected environments, the effects on survival and fitness are complex. One way to study this is to correlate measured noise levels with measured levels of baseline circulating stress hormones (glucocorticoids) in birds. The paper notes,
To date, no studies have simultaneously examined relationships among noise, GCs [glucocorticoids], and fitness in animals that settle and breed in natural areas exposed to chronic anthropogenic noise.
The paper looked at three species of cavity-nesting birds with different noise tolerances, in a New Mexico wildland which is now interrupted by an array of natural gas compressors. The evidence “strongly suggests that chronic anthropogenic noise induces stress and hypocorticism in birds.” Furthermore, with one of the studied species, the western bluebird, increased noise was correlated with a lower rate of hatching success.
There are a number of explanations for the stress response.
At lower exposure levels, anthropogenic noise is more likely to elicit stress responses indirectly by increasing the difficulty of coping with external challenges (e.g., territory defense) or by creating anxiety through reduced detectability and predictability of threats (e.g., acoustic masking of predator alarm sounds), or both.
Given the capacity for chronic noise to consistently mask biologically relevant cues, animals living in areas with high levels of noise may fail to receive information about their local habitats, leading to a continual state of perceived unpredictability and reduced security.
Citing a range of other studies, the authors further explain how chronic noise pollution disrupts the normal sensory perceptions of wildlife.
The distance over which birdsong and other sounds are effectively transmitted, their ‘active space’, is significantly reduced by increases in ambient background noise. Anthropogenic noise, acting as an acoustic blanket, can reduce or inhibit detection of hetero- and conspecific vocalizations that birds and other animals use to gain information about predation threats. For example, the presence of birdsong and chatter is thought to signal the absence of nearby predators.
How does noise pollution affect the wildlife in Westside and Bowmanville Marshes? Are there species which would otherwise make these wetlands home, if it weren’t for chronic noise levels? With increasing noise levels, will some of the existing species be driven out, or will the populations be weakened due to lower reproduction rates? These are complex questions – but they must be answered before the impacts of additional noise, due to a major mining/extraction project, can be properly assessed.
In spite of huge environmental challenges these wetlands remain home to a wide variety of species. Within this small area there are cattail marshes, open water, wetland forest, upland forest, and even a small fen. Among the many species that live here are various waterfowl, fish, wading birds, osprey, kingfisher, beaver, muskrat, and predators including otter, weasel, marten, raccoon, coyote and fox. These wetlands are also vital staging areas for the many migratory birds which fly over Lake Ontario in the spring and fall.
These wetlands are officially designated as “Provincially Significant Marshes”. The review process for the St. Marys under-the-lake mine must make us ask, how much significance does the province actually afford to this environment?
The authors of the paper on noise pollution and avian stress levels note,
In this era of unprecedented, large-scale human-driven environmental change, preservation or recovery of natural acoustic conditions should be a key aspect of conservation planning and is a critical step toward successful conservation of protected species.
Given the importance of natural acoustic conditions to conservation planning, should the province of Ontario give the OK to increased noise pollution from St. Marys Cement?
1“Chronic anthropogenic noise disrupts glucocorticoid signaling and has multiple effects on fitness in an avian community”, Proceedings of National Academy of Sciences, 14 November 2017