December 06, 2014
Baltic Sea Eutrophication And Climate Change

The lower levels of the Baltic Sea in northeast Europe have little oxygen (eutrophic) and efforts to raise sea oxygen by lowering sewage run-off and fertilizer run-off seem to be getting blocked by warming water. Of course, if the sewage run-off hadn't been reduced the oxygen levels would be lower still. Fish can't survive without oxygen. So this matters for fisheries production.

01 December 2014/Kiel. Despite extensive measures to protect the Baltic Sea from anthropogenic activities since the late 1980s, oxygen concentrations continue to decrease. Rising temperatures in the bottom water layers could be the reason for the oxygen decline.

The scientists think warming has counteracted efforts to reduce sewage flow into the Baltic. The sewage causes algae blooms and microorganisms eat the algae and consume oxygen in the process.

A natural phenomenon of the Baltic Sea is the lack of oxygen in the deeper water layers. The stratification of the Baltic Sea water is quite stable, with fresh saline and oxygen-rich water only reaching its inner regions from the North Sea through the Danish islands. "We see this also in Boknis Eck, from about 20 meters depth," explains Sinikka Lennartz, M.Sc., from GEOMAR and lead author of the new study. In the second half of the 20th century this natural phenomenon was augmented because countries bordering the Baltic Sea dumped large amounts of agricultural fertilizers and sewage into the sea. "That meant an oversupply of nutrients. Algae were then able to proliferate, and as soon as they die and sink to the bottom, microorganisms decompose the biomass and consume a lot of oxygen; this resulted in large oxygen-free zones at the bottom of the Baltic Sea to be formed " explains Lennartz.

What I want to know: could wind turbines pump air down into the water to increase the amount of oxygen in the water? Is the amount of needed wind turbines too much to be affordable? If this could be done would it boost the amount of fish by providing them with more food?

Alternatively, imagine sewage was diverted into a large lake and lots of air was pumped into the lake. Could such a lake serve as a large aquaculture farm? The Sea of Azov next to the Crimea is very eutrophic. Could it oxygenated to produce a big fish catch?

Share |      Randall Parker, 2014 December 06 12:04 PM 

bob sykes said at December 6, 2014 1:57 PM:

We have had the technology to treat sewage to very high levels of purity for 100 years. Furthermore, nitrogen and phosphorus removal has been required in the US for over 30 years. The Euros simply are refusing to pay for sewage treatment.

Benthal oxygen depletion is not the only problem arising from N/P pollution. A number marine algae excrete fish toxins and cause massive fish kills. The toxins also can kill people who eat the fish. Oysters, which are often eaten raw, are an especial problem.

jpstraley said at December 10, 2014 8:44 PM:

Large harvests of algae will remove nutrients & to a degree will also remove toxic pollutants. The Baltic has many political entities, so getting agreement might be the toughest task of all. In the long term, pretty serious controls on specific categories of pollution will be required. The truth is, that the human population, and the propensity of various actors to cheat their permits (or not bother obtaining permits) is likely to overwhelm civil controls. Fewer humans, accomplished over a couple of centuries, is the best answer...but that's pretty rational and thus damn near oxymoronic.

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