Open-Air Acoustic Laboratory in a World Biosphere Reserve: The Case of Lake Saint-Pierre, Canada

The St. Lawrence River is a large river system in North America, connecting the Great Lakes to the Atlantic Ocean (~1500 km) and is a major commercial waterway in the world. The fluvial portion has a highly diverse mosaic of habitats that support ~100 species of freshwater fish. Fed by numerous tributaries of varying quality, the St. Lawrence includes three large, shallow, slow-flowing fluvial lakes that alternate with narrow, fast-flowing stretches and numerous islands sometimes grouped in archipelagos, all of which are exposed to various anthropogenic pressures. Lake Saint-Pierre (LSP), located downstream, has been recognized as a World Biosphere Reserve (UNESCO, 2000) for its rich biodiversity and extensive wetlands. This UN status does not, however, protect it from the intense pressures associated with agricultural practices, water discharge regulation and, of special interest to us here, acoustic pressures, some of which are of particular concern. First, between 1952 and 1999, the Canadian Department of National Defense fired more than 500,000 projectiles at nearly the entire southern shore of the SLP. It is estimated that 7880 pieces of unexploded ordnance –UXOs – (3%) could remain with an explosive charge of 0.5–7.0 kg. For public safety reasons, a clearance, expected to last 9 years, has begun. Some UXOs will be removed and detonated at a land-based site, while those deemed too hazardous to be moved will be detonated directly in the lake, with the expectation that effective mitigation measures will be taken. These operations involve a vast 16,000 hectare area of shallow, highly productive habitat used for spawning and rearing by approximately 40 species of fish, some of which are threatened. Second, the navigation channel, which is ~300 m wide and ~ 12 m deep, is used year-round by commercial vessels, whose noise contribution to the soundscape has never been characterized in these fresh waters. In addition, during the ice-free season, the LSP and its archipelago are frequented by numerous recreational vessels, whose acoustic effects have not yet been measured. Also, the exposure to winds and waves of this large shallow lake is likely to generate significant ambient noise fluctuations, which would deserve to be quantified. Finally, there is great interest in characterizing biophony in this unique environment and testing some of the effects of underwater sound (including particle motion) and ground vibration on fish and invertebrates, especially during bombshell explosions. It is in this context that a joint academic-department acoustic research program has been initiated, with the aim of preparing a first portrait of the soundscape in this World Biosphere Reserve and possibly proposing recommendations for mitigation measures regarding the most important anthropogenic noise sources.