NOVEMBER 2008 — Before early light, fishers amble down the dock at Gimli Harbour. They’ll be on Lake Winnipeg pulling nets as the sun breaks through an overcast of gossamer clouds outstretched on the eastern horizon.
The productivity of the lake seems to know no bound. But another boom may lead to a bust in the linear growth of the annual lake fish harvest.
Scientists studying the lake have been telling us for some time that Lake Winnipeg is threatened. The principal threat, they say, is an excess of the nutrients nitrogen (N) and phosphorous (P). This nutrient over-loading has led to blooms of bluegreen algae that this year, as in past years over the last decade, covered much of the North Basin.
This year, a large bluegreen bloom took hold in the South Basin, near Victoria Beach and right up to the Narrows, where the two basins of the lake pinch off.
The bluegreen blooms are actually mats of a primitive bacteria known as cyanobacteria. Fishers glumly work through the thick mats of cyanobacteria, which cling to fishing nets and make their work more difficult. Rainbow smelt, a so-called introduced species, bob belly-up in the water, tainted blue and green by the bacteria.
There is no danger to the fish, which remain highly edible — among the favourites pickerel, sauger and whitefish. It’s the lake, a vast and complex aquatic ecosytstem, that’s in peril. Consequently, the fishery is in the biological snare, too. As goes the health of the lake, so the health of the $25-million fishery, an industry that employs about 1,000.
The cyanobacteria in Lake Winnipeg out-compete the plant algae we are all familiar with as the pond scum of our adventuresome youth. Cyanobacteria ‘out-compete’ because they can use nitrogen from the atmosphere. Plant algae can’t perform that feat, so they lose foothold in the competition for habitat.
The shift to cyanobacteria sets off a cascade of other consequences. When the increased biomass of bluegreens dies, it sinks to the bottom of the lake. The decomposition results in depletions in the oxygen column. This can affect other species.
The presence of dominant cyanobacteria species open new ecological niches for aquatic organisms that favour them in their diets.
In addition, some cyanobacteria release toxins that can be fatal to animals that ingest water containing them.
In all, the emergent prominence of cyanobacteria may be moving the lake to a precipice, — a threshold or tipping point — beyond which full recovery will be problematic.
Solutions exist to slow the process that has been advanced by nutrient over-loading. The obvious first solution is to reduce the over-loading at source. The problem is that there are millions of point sources across the one-million-square km Lake Winnipeg watershed. The watershed takes in a huge area, from the foothills of the Rockies in Alberta to Northwestern Ontario, dipping into four American states and covering most of Manitoba north to Hudson Bay.
Individual action and collective action can make a difference, as individuals and the cities and towns in the watershed consciously limit their use of compounds that contain phosphorous, such as automatic dishwashing detergent and lawn fertilizers. Leaking septic and holding tanks should be repaired to ensure they are not sending household waste into the surface and groundwater.
Municipalities can lead the way by removing phosphorous from their wastewater. Municipalities must also stop pumping effluent into waterways. Gimli, Lake Winnipeg’s largest population center, treats its sewage, then pumps the end product (effluent) into the lake. Its sewage treatment plant removes most of the phosphorous in raw sewage, but there is still a quantity of P that cannot be removed.
More, sewage treatment processes do not remove all parasites nor heavy metals or pharmaceuticals that wind up in household sewage. These are dumped into the lake.
A pair of surveys by the Canadian Geographical Survey in 1994 then again in 1996 linked the emergence of intensive farming in the early-1960s with an increase in P and N in Lake Winnipeg. The correlation was established after analyses of core samples during the two lake-wide surveys.
The surveys obtained samples from lake sediment. The deeper the core the further back in the life of the lake scientists could travel.
The surveys suggested that before fertizliers were used extensively, there was a lower concentration of the nutrients in the core samples.
Crops require P and N in concentrations that vary with the crop planted. In the ideal, fertilizer should be applied at the optimal agronomic rate — which is simply the concentration at which there is full utilization of the applied nutrients by the plants. When applied in excess of crop need, the unused nutrients can leave the land, enter local drainages, then Lake Winnipeg.
Farmers are not alone in the drama of over-fertilization.
Municipalities, cottagers and other jurisdictions also send nutrients and pollutants into the lake.
Lake Winnipeg’s watershed spans four provinces and four central states in the United States. From the foothills of the Rockies east to Lake of the Woods, the Lake Winnipeg watershed takes in a vast landscape. Whatever comes off that landscape eventually drains into the waters of Lake Winnipeg.
The nutrients P and N are linked directly to the nutrient overload, which is causing the over-fertilization known among scientists as cultural eutrophication. At some threshold, the lake will die unless resolute action is taken.
Coordinated action across the watershed is needed. There’s been the promise of just such an effort, but it has been woefully slow in materializing. The federal government pledged $18 million by November 2007. At this writing (November 2008) not a penny has been spent of that pledged money.
In addition to reducing our nutrient footprint in all waterways, we must conduct the research so vital to understanding how these bodies of water behave.
We’d better be quicker at the task, more directed at the helm.
It’s increasingly clear, for instance, that looming climate change (the loss of glaciers in the Rockies, for instance) will exacerbate current conditions.
Nutrient loading, then, is not the only problem. Climate change could result in dramatic changes. As well, the arrival of new species of fish and microorganisms will disrupt the aquatic balance.
There is a crippling inertia when it comes to Lake Winnipeg. It one of the world’s least studied lakes of its size — both in its own area (about 24,000 sq. km.) and the area of its watershed.
We may lick the nutrient over-loading problem, but there are other challenges on the horizon. Rainbow smelt, introduced from the Winnipeg River system in the early-1990s, is now plentiful. Just how it’s changing the lake is a matter of conjecture. So little is known about the condition of the lake pre-introduction, it becomes a conundrum as to what ‘changes’ may have occurred or may yet occur.
Add to that the fact that the Devils Lake outlet in North Dakota operated this summer and the likelihood of ‘new’, non-native species being introduced — and one realizes the extent of the challenge.
The nutrient problem may be the easiest one to tackle — because real action can make a difference over time. Dealing with invasive species once they’ve arrived will prove a much greater challenge. Anticipating the effects of climate change is also unresolved in detail, though water shortages (reduced lake inflows) appear a likely result.
What Lake Winnipeg needs is some TLC; some focussed attention.
The province’s Lake Winnipeg Action Plan must be revisited. It recommends reducing the concentration of N and P to pre-1970 levels. That’s not nearly ambitious enough.
A 1974 study commissioned by the province urged immediate attention to the N-P problem. Twenty-four years on we appear no farther ahead.
“A comprehensive study should be commenced as soon as possible to prevent further degradation of Lake Winnipeg and to determine possible methods of lake restoration.”
“The nutrients in the lake make the water particularly fertile and predisposed to algae bloom whenever the appropriate climatic conditions occur.”
“A comprehensive water quality study of Lake Winnipeg and of the contributing drainage is required. Since it appears the main concern in this lake is aquatic blooms, the study should be carried out with major emphasis on the identification of nutrient inputs and the effect of control measures.
“The study should be commenced as soon as possible to prevent further degradation of this important water resource and to determine possible methods of lake restoration.”
— SOURCE: “Water Quality Study: South Portion of Lake Winnipeg”, 1974. Department of Mines, Resources and Environmental Management, Environmental Management Division, Environmental Protection Branch.