WhatFinger


Pond scum as an energy source

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In a recent paper on the eutrophication—over fertilization — of Canada’s Lake Winnipeg with the subtitle “Greening under global change,” [1] the authors show that the lake’s problem of blue-green algae blooms is based on increased loadings with phosphate and nitrate. These derive from sewage input by the city of Winnipeg and runoff from watershed sources, primarily farmland and livestock.
Lake Winnipeg, approximately 25,000 square kilometers (10,000 square miles) in size, is located in Manitoba, north of North Dakota and Minnesota. Its watershed extends into the US through its Red River tributary.

Filamentous Algae

Filamentous blue-green algae (cyanobacteria) are plants that thrive in over-fertilized (eutrophic) freshwater. They were a major problem in the lower Great Lakes, especially Lake Erie during the 1950s and '60s. Visible and odorous manifestations of the masses of decaying filamentous algae washed up on the shores. The main culprit was identified as the alga Cladophora sp., also known as pond-scum. That’s’ the same stuff President Obama wants the U.S. to use as an energy source [2]. As a resident I say: Be my guest, harvest all you can – free for the taking!

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Sarcasm Aside

Seriously, blooms of these algae are a nuisance, not least because of their odorous decomposition. If not washed up along the shores, the algae sink to the lake bottom and decay there. That can lead to oxygen depletion in the overlying water which makes it uninhabitable or toxic for many natural organisms such as fish and midges which a lake needs in order to have a functioning ecosystem. If you think Lake Winnipeg is near to boiling, I can tell you otherwise. Many years ago, I drove “out west” in late July in a Volkswagen beetle. As my British friends might have said “it was bloody hot.” The air temperature was about 110 F and, of course, we had no air-conditioning in the car. When coming by Lake Winnipeg, it was absolutely irresistible to go for a refreshing swim. Our dip was quite refreshing, but it lasted for only a few seconds. Even in the heat of summer, after weeks of hot weather, the water temperature was still well below anything comfortable; the term frigid is still benevolent.

Lake “Greening”

The “greening” of previously “blue” lakes is really a sign of over-fertilization (eutrophication). Whether in Switzerland, Canada, South Africa or elsewhere, the algae respond to excessive nutrient loadings and multiply rapidly. Their increasing abundance in the Great Lakes of North America, especially Lake Erie, led to the “Great Lakes Water Quality Agreement of 1972” [3] which established requirements for decreased nutrient loadings from municipalities in the watershed. The implementation resulted in the previously “dead” Lake Erie springing back to life with large populations of walleye (in Canada more commonly known as pickerel), bass and other fish species. Green-looking lakes are not necessarily bad. It really depends on a variety of conditions. For example, Lake of the Woods (LW), straddling the Minnesota/Manitoba/Ontario borders, is in some parts very green. Until “turnover,” its surface water looks like “pea soup.” Still, the lake supports healthy populations of walleye, crappie and musky, sought after by anglers and commercial fisheries alike. What sets LW apart from (formerly) “dead” Lake Erie is that its bottom water does not become devoid of oxygen.

Temperature

Many northern lakes, such as Lake Winnipeg are cold and nutrient poor. During summer, a thin layer of surface water may become bearable to swim in for a brief period only. When exposed to strong nutrient loadings, such lakes develop spring time algae blooms before a corresponding adjustment in zoo-plankton and fish populations can take place. However, over a few years time the upper trophic levels will eventually respond too with increased populations of fish. Water temperature is certainly one of several parameters driving any lake’s biological system. However, nutrient loadings, especially phosphorous (P) and nitrogen (N) loadings are most critical. They can be beneficial for the lake or not. Light and nutrient supplies are the main determinants for algae growth, also known as primary production. For example, in the Arctic, salmon feed on the small shrimp harvesting lower food chain organisms off the underside of the sea ice. That was one of the scientific side discoveries of the submarine USS Nautilus in 1958. Even with a thick layer of ice and snow sufficient light penetrates to the water beneath to keep the biological system going year round.

Change

Neither so-called global warming nor climate change determines algae growth. Nutrient supply is the controlling factor, as shown by Schindler et al. and others before them. Moreover carbon dioxide, a nutrient by itself, is rarely a growth-limiting factor, but P and N are. Lake Winnipeg’s eutrophication problems may well be exacerbated by “global change.” However, that has nothing to do with water temperature but only with the potential for increased nutrient loadings from the catchment basin, based on models which predict increased precipitation. [1] Schindler DW, et al., 2012. [2] Kaiser KLE, 2012. [3] GLWA, 1972.


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Dr. Klaus L.E. Kaiser -- Bio and Archives

Dr. Klaus L.E. Kaiser is author of CONVENIENT MYTHS, the green revolution – perceptions, politics, and facts Convenient Myths


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