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Straw can control algae


Investigations at the Aquatic Weeds Research Unit, of Britain's Agricultural and Food Research Council's Institute of Arable Crops Research, suggest a novel solution to two major environmental problems - blue-green algae blooms in lakes and reservoirs, and algae blanket weed that blocks drainage and irrigation channels.

Studies at the unit have shown that barley straw could be used to help control algae growth in water and tackle the problems caused by filamentous green algae blocking drainage pumps and sluices, and by toxic blue-green algae which are producing blooms in some reservoirs that are poisonous to animals and humans.




This research began after a farmer observed that the algae in his lake decreased greatly one summer after old and rotten bales of hay had fallen into the water during the previous winter. Initially, it was thought that this effect was probably due to absorption of nitrate and phosphate from the water by micro-organisms decomposing the hay, so that these nutrients were no longer available to the algae.

In laboratory tests it was confirmed that straw had the same effect as hay, although experimental addition of straw to a lake did not deplete nutrients and algae growth was unimpaired. However, the following year, there was virtually no algae growth in the lake, which was normally badly infested with algae every year.


Surprising Finding


The suppression of the algae was found to be due to one or more algistatic chemicals being produced as the straw rotted. The effective chemical compound is produced only when the straw decomposes in the presence of oxygen, supporting the observation that tightly packed bales which can become anaerobic are not the best method of application.

One of the most surprising findings has been that very little straw is needed, 10 g of straw per cubic metre of water being sufficient to inhibit algae growth. This is equivalent to two to three bales per hectare (one half to one bale per acre) of water, assuming an average depth of about 1one metre. A wide range of freshwater algae is inhibited with this technique.

Several field experiments are in progress. One has been running for six years, extra straw being added twice yearly.

Results are encouraging. Lake owners who have experimented with barley straw report excellent results, with clear water and healthy fish stocks.


Copyright 1991 REAP Canada

Reprinted with permission. All rights reserved.

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