Algal blooms are localized algal diffusions that occur under optimal conditions for algae growth and reduced pressure from predation. When specific microalgae, especially cyanobacterial bacteria, reach high levels of enrichment in an outbreak, the outbreak exhibits harmful characteristics (Figure 1). Although these microalgae species account for only a small part of the natural world, they can produce harmful or toxic substances that cause a variety of adverse effects, including the destruction of the food chain, animal deaths, and serious human health hazards (Baidu Encyclopedia). Perhaps people did not think that this small algae would have such a huge impact on human society, in the United States alone, the phenomenon of harmful algal blooms in freshwater water bodies caused about $4 billion in economic losses each year.
Figure 1 Xingkai Lake (left) on the Sino-Russian border and St. Petersburg on the US-Canada border. Clair Lake (right) has varying degrees of algal blooms
In recent years, reports and studies on harmful algal blooms in water bodies such as lakes are increasing year by year, but there is no clear research data on the extent of algal blooms in lakes worldwide, and the relationship between human activities and the impact of climate change on algal blooms is not clear.
Recently, researchers from the Carnegie Institution and NASA in the United States published an article in the international top journal Nature on this issue, conducting the first systematic survey and analysis of dozens of large freshwater lakes around the world (Figure 2), and the results show that the intensity of summer algae outbreaks has indeed increased in the past 30 years.
Figure 2 Degree of change in the degree of algal bloom at the study site since 1980
Although the huge impact of harmful algal blooms has long been noted, scientists have long studied freshwater algal blooms either in a single lake or in specific areas, or in a relatively short period of time. To date, there has been no long-term, global-scale study of freshwater algal blooms. In view of this, the researchers obtained nearly 30 years of high-resolution (30m) satellite data through the Us Landsat 5 near-Earth satellite, selected 71 large lakes in 33 countries/regions on six continents for long-term comparative analysis, obtained 72 billion data points, and finally revealed the long-term trend of summer algae mass reproduction with the help of Google Earth Engine.
The results show that the peak intensity of summer algal blooms increased significantly in more than two-thirds of lakes, with only 6 lakes having a downward trend (Figure 3), suggesting that algal blooms are actually becoming more common and intense. On the other hand, although the trend of global lake algal blooms deteriorating is very obvious, the reasons for the deterioration of algal blooms seem to vary from lake to lake. The researchers, taking into account factors such as fertilizer use, rainfall or temperature, found that the deterioration of algal blooms did not coincide between different lakes.
Figure 3 Spatial-temporal distribution of the phenomenon of point algal blooms
The researchers also pointed out that the impact of climate change on lake algal blooms is obvious, and warming has hindered the speed of lake algal blooms self-repair to some extent. The above research results were published in the latest issue of Nature, for details, please click at the bottom of the article to read the original article and consult the article.
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