10. Mer Bleue Bog
Boreal peatland in abandoned channel of early Ottawa River
Mer Bleue Bog
East end of Ridge Rd., Ottawa, Ont.
Mer Bleue lies on the floor of an ancient river channel, informally called the Mer Bleue channel, which was cut into the unconsolidated sediments of the postglacial Champlain Sea about 9000 years before present by the Ottawa River. These sediments consist of thick (25-100 m) deposits of marine clay and clayey-silt (informally called Leda Clay) capped by a sand delta.
During the last ice age, the weight of the glaciers depressed the surface of the earth. As the glaciers began to melt away from this area about 12000 yrs BP, the Atlantic Ocean invaded the Ottawa and St. Lawrence River valleys, creating a temporary sea - the Champlain Sea. Vast amounts of clay were deposited in this sea. As the land surface slowly rose to its current elevation, the Sea retreated and the Ottawa River and its tributaries began to erode broad valleys into the sediment of the sea bottom. At this time, swollen by glacial meltwater, the early Ottawa River was much larger than today and occupied many channels. Most channels were abandoned about 8000 yrs. BP, when river discharge drastically dropped after Hudson Bay became ice-free. Since abandonment, peat has accumulated in Mer Bleue Bog to thicknesses of up to 6 metres. A radiocarbon age of 7650 yrs. B.P. from basal peat established the age of the bog.
The impermeable nature of the clay that underlies a depression in the channel floor accounts for the slow accumulation of peat forming the bog. The western side of the bog is characterized by 3 long arms divided by long narrow sand ridges that were deposited by the early Ottawa River. Anderson Road traverses these arms of the bog and sand ridges. Excellent signage describing the geological history is available near the boardwalk parking lot at the end of Ridge Road.
Mer Bleue Bog is one of the largest bogs in southern Ontario. It is a remarkable boreal-like ecosystem normally found in the far north. Interpretive signs along the boardwalk guide you through the development and biology of a bog.
The following flora description is reprinted from Mer Bleue Conservation report
Mer Bleue is a boreal peatland which is usually found in the boreal forest to the north. The sphagnum bog contains two main types of vegetation - the black spruce forest and the open heath vegetation. The black spruce (Picea mariana) forest is dominated by the black spruce and some larch (Larix laricina), trembling aspen (Populus tremuloides) and grey or white birch (Betula spp.) Sphagnum spp. are the dominant low lying form of vegetation in the bog. About 12 species of heaths thrive in the bog. The most common being Labrador tea (Ledum groenlandicum), leatherleaf (Chamaedaphne sp.), small cranberry (Vaccinium oxycoccus), bog-laurel (Kalmia prolifolia) and sheep-laurel (K. augustifolia). At least nine species of orchids (Orchidaceae spp.) are found in Mer Bleue along with a variety of cottongrasses (Eriophorum spp) and sedges (Cyperaceae spp.). The marsh areas around Mer Bleue are characterized by plants such as cattails, alders (Alnus rugosa), willows (Salix sp.) and sedges (Cyperaceae spp.). There are several aspen islands in the centre of Mer Bleue consisting of an overstory of aspen and an understory dominated by bracken fern.