Aquatic blooms of algae or cyanobacteria (sometimes called blue-green algae, though they are a type of photosynthesizing bacteria, not algae) can be a nuisance – and they can also be dangerous.
“[B]looms of cyanobacteria pose a serious threat to drinking water sources worldwide because many taxa contain harmful hepato- and neurotoxins,” write the authors of a paper recently published in the journal Ecology Letters.
Scientists studying blooms of cyanobacteria or algae often narrow their focus to a single location and a short time-frame, sometimes just a single season or a few years. Those studies can be enlightening, and can help managers working to prevent future blooms (and I have written about a couple of them in the past), but large-scale studies emphasizing general trends across multiple centuries can also add to our understanding of algae or cyanobacteria blooms.
A team of researchers compiled data from 108 studies, each of which included a historical record, dating back about 200 years, of “paleolimnological pigment,” the residue that cyanobacteria and other organisms left behind in lake sediments. The researchers limited their study to temperate and sub-Arctic lakes, so most of the lakes they included in their analysis were located in North America and Europe.
The scientists found that cyanobacteria, more than other types of phytoplankton, have become more prevalent over the last 200 years, and especially so since about 1945. By including environmental conditions in their analysis, like lake depth, nutrient levels, and temperature, they were able to determine that, at least on the continent- and century-wide scale they studied, increasing nutrient fertilization was the factor most associated with increases in cyanobacteria.
The researchers also studied serial measurements of nutrients and cyanobacteria taken directly from the water column of 18 lakes over multiple years (rather than historical data from sediment cores). The lakes with decreasing nutrients over time also had fewer cyanobacteria, suggesting that restoring lakes by curtailing nutrient inputs may be an effective way to prevent future cyanobacteria blooms.
Cyanobacteria blooms can be problematic and hazardous – but by managing the human activities that impact lakes, it may be possible to avoid at least some of them.