Effects of climate change the main cause of death of thousands of fish at Lake Oanab

By Dr Moses Amweelo

WHEN TALKING about the impacts of climate change, we mostly hear about changes to land and the planet’s surface or atmosphere.

However, most of the warming is going on in sea water, lakes and rivers where many ecosystem changes are also occurring.

As explained by the US agency, the National Oceanic and Atmospheric Administration (NOAA), the basic chemistry of ocean or lake water acidification is well understood.

These are the three main concepts: more carbon dioxide (CO2) in the atmosphere means more CO2 in the ocean or lake water; atmospheric CO2 is dissolved in the ocean or lake water which becomes more acidic; the resulting changes in the chemistry of the oceans or lake water disrupts the ability of plants and animals like fish in the sea or lake water to make shells and skeletons of calcium carbonate, while dissolving shells already formed.

We have witnessed the death of thousands of fish at Lake Oanab near Rehoboth recently, which might be caused by organic material, when more rainfall increases the amount of organic material flowing into the lake’s water.

Organic material, or natural organic matter, refers to the large pool of carbon-based compounds found within natural and engineering, terrestrial and aquatic environments. Organic molecules can also be made by chemical reactions that do not involve life.

Organic material is very important in the movement of nutrients in the environment and plays a role in water retention on the surface of the planet. Swedish researchers recreated the conditions found in the Bothnian sea estuary.

They discovered that as temperatures increase, there is an increased run-off of organic material into the world’s oceans and lakes. This encourages the growth of bacteria at the expense of phytoplankton.

Dr Erik Bjorn from Umea University says: “When bacteria become abundant in the water there is also a growth of a new type of predators that feed on bacteria.”

Under the warmest climate scenario suggested by the Intergovernmental Panel on Climate Change (IPCC), there would be an increase in organic material run-off of 15-20 percent by the end of this century.  This in turn would see levels of methylmercury in zooplankton, the bottom link in the food chain, grow between two- and seven-fold. The researchers said that different parts of the world will suffer different impacts, with lakes and coastal waters in the northern hemisphere being the most likely to have significant increases in methylmercury levels in fish, while the Mediterranean, the central US and Southern Africa will likely see a reduction. The question is what is the potential solution on organic material which causes the fish in oceans and lakes to die? Water with organic material can be disinfected with ozone-initiated radical reactions.

The ozone (three oxygens) has very strong oxidation characteristics. It can form hydroxyl radicals when it decomposes, which will react with the organic material to shut down the problem of biofouling.

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March 2017
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