Blue-green algae, also known as cyanobacteria, are microscopic organisms that live in water and can produce toxins that are harmful to humans and animals.
Blue-green algae blooms occur when these organisms grow rapidly and form dense mats or scums on the water's surface.
Blooms can cause various problems, such as discoloring the water, producing foul odors, impairing water quality, and affecting aquatic life.
These are often associated with warm, calm, and sunny weather conditions, as well as high levels of nutrients such as phosphorus and nitrogen in the water.
These factors can stimulate the growth and reproduction of cyanobacteria, especially in shallow and stagnant waters.
However, a recent study by researchers from Laval University in Canada and their collaborators in Uruguay has found that water temperature has little to no impact on the development of blue-green algae blooms.
How to measure blue-green algae blooms
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The researchers used data from 464 lakes in North and South America, spanning a latitudinal gradient of 14,000 km from Tierra del Fuego in Argentina to Ellesmere Island in Nunavut.
These lakes are located in different climatic zones, ranging from equatorial to polar, as per Phys.org.
The researchers measured the biomass of cyanobacteria in these lakes using satellite imagery. Biomass is an indicator of the amount of living organisms in a given area or volume.
The researchers used a remote sensing technique called MERIS (Medium Resolution Imaging Spectrometer), which can detect the reflectance of light from cyanobacteria pigments in the water.
The researchers also measured various environmental factors that could influence the biomass of cyanobacteria, such as water temperature, nutrient concentrations, light availability, precipitation, wind speed, and lake morphology.
They used statistical models to analyze the relationships between these factors and cyanobacteria biomass.
The researchers found that water temperature had no clear association with cyanobacteria biomass across the latitudinal gradient, as per the CDC.
This means that blue-green algae blooms can occur in both cold and warm waters, as long as other favorable conditions are present.
The researchers also found that the main factor explaining the variations in cyanobacteria biomass across the Americas was the concentration of phosphorus in lake water.
Phosphorus is an essential nutrient for cyanobacteria growth and is often limiting in aquatic ecosystems. Other factors that had significant effects on cyanobacteria biomass were nitrogen concentration (in lakes less than three meters deep), light availability (in lakes more than three meters deep), and wind speed (in lakes more than 10 meters deep).
The researchers concluded that blue-green algae blooms are mainly driven by nutrient availability rather than temperature.
They suggested that this finding could have implications for predicting and managing blue-green algae blooms under future climate change scenarios
The study by the Laval University researchers and their collaborators is one of the first to use satellite imagery to assess the biomass of cyanobacteria across a large spatial scale.
It shows that blue-green algae blooms can occur in a wide range of climatic conditions and are not limited by water temperature.
The study has implications for understanding and managing blue-green algae blooms in different regions and seasons.
It can help to identify the lakes that are most vulnerable to cyanobacteria proliferation and to implement measures to reduce nutrient inputs from natural runoff, lake sediments, and human activities.
Moreover, it can help to monitor the changes in cyanobacteria biomass over time and space using remote sensing techniques.
The researchers plan to further investigate the causes and consequences of blue-green algae blooms in different aquatic ecosystems.
They hope to collect more data from other sources, such as field measurements, laboratory experiments, and numerical simulations, to validate and complement their satellite observations.
They also aim to explore the effects of blue-green algae blooms on water quality, ecosystem function, and human health.
