A River on the Edge
Granite meets limestone. Uplands meet lowlands. Black spruce and jack pine meet white spruce and birch, and murky, tea-stained waterways meet transparent, turquoise-blue lakes.

Like an outline on a physiographic map, the Grass River defines the meeting point of 2 geological zones and ecoregions. It marks the uneven boundary between the ancient North American Precambrian Shield - commonly known as the Canadian Shield - and the vast boreal plain of the Manitoba Lowlands, underlain by flat beds of softer sedimentary rock.

To the north and west, where the river washes over the Shield, it barely covers the granite bedrock. Its shallow lakes and pools are sprinkled with protruding islands and rocky outcroppings, and the water has a brownish tinge, darkened by the tannic acid that seeps from its geological foundation. But along its southern shore, where the Grass skirts the northern edge of the Manitoba Plain, its lakes sparkle with a brilliant blue. Their limestone bottoms act to neutralize the acids and keep the water clear.

The geological dividing line of the Grass River also corresponds to differences in ecological character. While most of the waterway lies in the ecoregion known as the Churchill River Uplands, its southwestern reaches dip south into the Mid-Boreal Lowlands:

Churchill River Uplands
• Located along the southern edge of the Precambrian Shield in north-central Saskatchewan and Manitoba.
• Marked by cool summers and very cold winters.
• Part of the continuous coniferous boreal forest that extends from northwestern Ontario to Great Slave Lake.
• Predominant vegetation is black spruce, jack pine, with a shrub layer and ground cover of lichens and mosses.
• Permafrost is distributed throughout the region in organic deposits.
• Small to large lakes comprise 30 - 40% of the land surface, with drainage northeastward via the Churchill, Nelson and Seal river systems.
• Wildlife includes caribou, moose, black bear, lynx, wolf, beaver, muskrat, snowshoe hare and red-backed vole.
• Bird species include raven, common loon, spruce grouse, bald eagle, gray jay, hawk owl and several species of waterfowl.
• Major urban centre: Flin Flon.

Mid-Boreal Lowlands
• Located in the northern section of the Manitoba Plain from the eastern shore of Lake Winnipeg to the Cumberland Lowlands of Saskatchewan.
• Marked by short, warm summers and cold winters.
• Part of the boreal mixed coniferous and deciduous forest extending from northwestern Ontario to the foothills of the Rocky Mountains.
• Flat, low-lying region with extensive wetlands covering approximately half the area.
• Predominant vegetation is trembling aspen, balsam poplar, white and black spruce and balsam fir.
• Permafrost occurs in isolated patches in northeastern sections.
• Wildlife includes moose, black bear, wolf, lynx, and snowshoe hare.
• Bird species include waterfowl, pelican, sandhill crane, ruffed grouse.
• Major urban centres: The Pas and Grand Rapids.

Lacy Limestone: The Karst Formations of the Grass River

One of the greatest contrasts between the granite bedrock of the Grass River's northern reaches, and the limestone pavement of its lower watershed, is permeability. While the hard rock of the Canadian Shield resists the penetrating effects of rainfall, the exposed sections of the carbonate bedrock of the boreal plain are subject to dissolution, crumbling and collapse. A series of underground caves and channels in the lower reaches of the Grass mark the areas where the limestone of the lowlands has begun to give way to the forces of nature.

A hollow, honeycomb-like "karst" landscape feature is formed when carbonate rock is dissolved by precipitation. As rain falls through the atmosphere, it absorbs carbon dioxide. Over time, the resulting solution of weak carbonic acid eats away at the limestone. Cracks and crevices form, and pores enlarge. More and more water pours in, accelerating the dissolution process, and creating a lacy, underground drainage network of channels and pipelines. Gradually, the fractured subsurface becomes filled with vertical shafts, underwater springs and underground caves. In some cases, the growth of the void below leaves only a thin roof of rock above; the roof collapses, and a large, gaping sinkhole appears in the ground.

Tracking Manitoba's Woodland Caribou
It's a habitat made for caribou: old-growth forests with abundant lichens, islands and muskegs for protected, predator-free calving, and a sparsely-distributed human population. The Grass River watershed is within the range of Manitoba's boreal forest woodland caribou, a 14-herd population that totals 2,000 - 2,500 animals. (The province has 2 additional coastal woodland caribou herds near Hudson Bay.) Although the Manitoba caribou herds do not appear to be experiencing the steep declines of several western populations, there is increasing concern that mining, forestry and other industrial developments are beginning to place some herds at risk.

Caribou tracking programs in Manitoba are being carried out as part of the provincial government's Woodland Caribou Range Management Strategy. Regional committees, such as the Northwest Region Woodland Caribou Management and Research Committee, have been established as joint projects of government, the forestry industry, conservation groups and aboriginal nations. Radio-telemetry tracking programs and field observations are being used to generate precise information about herd sizes and ranges, and to develop a management strategy that directs development away from critical caribou habitats.

In the Grass River region, more than 2 dozen caribou have been equipped with radio collars that transmit signals to airplane receivers. Using modern technology, airborne wildlife biologists are able to track the movements of the animals and identify their wintering and calving locations.