Fresh Ideas: More than 400 ‘dead zones’ in world’s waters

When I was seven years old and newly arrived in the United States, I went swimming at Baldwin Lake in Greenville, Mich., every chance I got. It was a relatively small lake nestled below a foreste∑d cemetery on the east and “wild” woods on the west. The country club was on the hill as one approached the lake, and cottages dotted the shoreline all around except for one designated section that was the beach. About 15 years ago the city began “oxygenating” the lake every spring because eutrophication had set in.

Normally, eutrophication is a natural process that occurs over many centuries and involves the gradual reduction of oxygen in bodies of water which results in more plant, rather than aquatic (fish, crab, etc.) life. It’s not restricted to lakes, but is prevalent in bays, estuaries, and marginal seas. Today, due to human activity, it has accelerated dramatically and dangerously to the point where it also occurs along populated coastal areas of oceans.

Typically, we recognize eutrophication as “algal blooms,” those bright green, but also brownish-yellow, or even red, slimy algae that reek of rich nitrogen and phosphorus which usually occur once a year in summer or when the weather and water become warmer than usual — which is pretty much a “given” now. “Algal bloom” is such an innocent, almost lovely image, but it’s similar to the poisoned apple the witch gives Snow White: taking a bite is death.

The Baltic Sea is but one example of oxygen depletion that’s 10 times worse now than it was 100 years ago. According to Arhus University in Denmark, the “dead zone” in the Baltic is now one and a half times the total area of Denmark. Not only warmer weather and water encourage the growth of algae, but so do the humanly produced fertilizers (especially nitrogen and phosphorus), detergents, industrial waste, animal and human waste.

As of 2008, there were 405 “dead zones” (low oxygen levels) in the world’s oceans and large lakes. Oxygenation, pumping oxygen down into the seabed, helps, but even at that, it takes decades for healthy fauna to return and replace the bacteria rich infested bottoms.

A further problem is some algae produce neurotoxins — often called HABs or Harmful Algal Blooms. These are not always recognized or visible. For instance, the deaths of 400 sea lions in Monterey Bay in May and June of 1998 were initially a great mystery. Only after molecular probes were done did scientists determine the deaths were linked to a short but deadly algal bloom called pseudo-nitzscia australis. This toxin was cited as the one responsible for the earlier 1991 deaths of 100 brown pelicans in Monterey.

Toxins also affect fish, sometimes killing them outright; other times in more subtle ways. Did you know, for instance, that farmed salmon is genetically different from wild salmon and more susceptible to diseases? Farmed salmon often escape their farms and slip into the ocean where they are in a position to gradually alter the wild salmon by undermining their immune systems. The whitefish of the Great Lakes, often referred to as “the king of freshwater fish,” is in jeopardy. An article in the 2010 Journal of Great Lakes Research points out there has been a recent decline in its “fish growth rates and body condition.” In other words, whitefish immune systems are compromised. It was too contaminated to eat back in the 70s, but it has come back — yet not fully.

As for Baldwin Lake, people still swim there, but I don’t see any fishermen.

Ursula Carlson, Ph.D., is professor emerita at Western Nevada College.


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