Prairie by Candace Savage

Author:Candace Savage
Language: eng
Format: epub
Tags: Nature, NAT011000
ISBN: 9781553658993
Publisher: Douglas & McIntyre
Published: 2011-01-18T16:00:00+00:00

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How Prairie Potholes Work

At first glance, a slough does not appear to have the makings of a biological powerhouse. What is it, in the final analysis, but a pool of stagnant water? Sunk into poorly sorted glacial rubble that inhibits organized flow, a typical pothole has only weak and fitful connections with the surrounding groundwater. Depending on the circumstances, any given pothole may receive water through seepage, lose it through underground leaks, or experience both input and outflow through different parts of the basin simultaneously. A slough that receives an influx of groundwater is also typically hit with a burden of dissolved salts picked up from the underlying geological formations. If this briny solution is permitted to escape from the basin either through overbank flooding or underground leaks, the salts flow out with the water and tend not to accumulate. But if the basin has no outlet, the water gradually evaporates, the concentration of salts builds up, and the wetland becomes saline (with chlorides) or alkaline (with sulfates). Some prairie potholes are ten times as salty as the sea, surely pushing the limits of habitability.

Sloughs also present a variety of other potentially life-threatening challenges. In the swampy warmth of midsummer, as submersed plants die back and rot, the water becomes starved for oxygen—if there’s still water left to starve. Like playas, prairie potholes are notoriously unstable, typically filling in spring and dwindling over a period of weeks or months, with little chance of renewal before the next spring thaw. How long water persists varies from pothole to pothole and from year to year, in response to such variables as the depth of the basin, flow to and from the groundwater, and the uncertainties of the weather. Depending on its duration, a slough may be classified as ephemeral, that is, a thin layer, or sheet, of water that lasts for a matter of days; temporary, a puddle that persists into early summer; seasonal, a pond that dries out annually but that often remains wet till fall; or permanent, a wetland that withstands all but the most severe droughts. (This last category includes such birding hotspots as Delta and Oak Hammond marshes in Manitoba, Last Mountain Lake and the Quill Lakes in Saskatchewan, and Beaverhill Lake in Alberta, all of which have been honored as Wetlands of International Importance under the un’s Ramsar Convention on Wetlands.) And these distinctions are all overridden by the insult of the northern winter, which closes in on wetlands regardless of their status and deprives them of light, warmth, and other necessities.

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