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Algae is a diverse group of aquatic, plant-like organisms with simple structures, varying from single-celled phytoplankton (microalgae) floating in the water to large seaweeds (macroalgae) attached to the ocean floor. These algae colonies can grow excessively and produce toxins under favourable environmental conditions, such as increased temperature and nutrients. Many harmful algae blooms often occur in bodies of freshwater and occasionally in marine water, posing a threat to aquatic ecosystem health and human drinking water supplies. 

Most phytoplankton are microscopic organisms, but they can grow in colonies large enough to be noticeable to the human eye. In freshwater, phytoplankton are made up of green algae and cyanobacteria, also known as blue-green algae; whereas marine phytoplankton are mainly composed of microalgae known as dinoflagellates and diatoms. They are key primary producers (photoautotrophs) that support biogeochemical cycling, structure of food web and the sustainability of aquatic ecosystems. 

An algal bloom is a rapid increase in algae populations in freshwater or marine water systems, resulting from an excess of nutrients in water, particularly phosphorus and nitrogen, in a process known as eutrophication. These blooms can occur seasonally, after an upwelling of nutrient-rich water, or due to pollution from human activities such as agricultural runoff, inadequate sewage treatment and runoff from roads. The presence of high levels of nutrients together with warm, sunny and calm conditions, create an ideal environment for phytoplankton productivity. However, algal blooms may also be of concern as some species of algae produce toxins. Moreover, when the abundant algae die off and decompose, the dissolved oxygen content decreases, causing hypoxic, or “dead” zones, conditions in which marine life cannot survive. 

Cyanobacteria are often the species of toxic algae and commonly live in freshwater. Excessive growth of cyanobacteria can release cyanotoxins, resulting in harmful algal blooms (HABs), which cause damage to freshwater ecosystems and the economy, harm wildlife, livestock and pets, threaten public health and contaminate drinking water supplies. 

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However, cyanobacteria are just one growing concern that water utilities face. While not all cyanobacteria produce cyanotoxins, some produce unpleasant taste and odours. They can also interfere with the process of drinking water treatment, by increasing the occurrence of potentially harmful disinfectant byproducts. The cost of removing cyanotoxins in drinking water is also expensive and is typically passed on to water customers. 

For example, in 2014, a harmful algal bloom event occurred in Lake Erie (North America) that left more than 400 000 people in the city of Toledo without a usable water supply for two days. The toxic algae overburdened the local drinking water supply utility and made their way into the water supply system. To cope with the contamination, the city allocated USD$4 million for water treatment chemicals.

Climate change is increasing the frequency and severity of HABs due to warming water temperatures, more sustained droughts and increased flooding. Droughts can reduce the flows in freshwater bodies and increase competition for ever-scarcer freshwater supplies. The remaining water in the water bodies will become warmer and more stagnant. Low flows in waterways may also reduce dilution of and increase the concentration of nutrients, which stimulate algal growth. On the other hand, heavy rainfall events can induce more algal blooms by flushing large amounts of sediments and nutrients into water systems through runoff.

According to Paerl et al. (2018), the linkage between excess nutrient inputs and HABs has been widely recognised in European and North American waters impacted by large-scale agriculture, industrialisation and urbanisation. There is also a rapidly increasing trend in developing regions of Asia, Central and South America, Africa, Australia−New Zealand and the Pacific Basin. Human hydrologic modifications such as water withdrawals, diversions and dams have additionally altered the flow regimes of water and nutrients entering aquatic ecosystems.

Furthermore, research published in Nature in 2019 indicated that harmful algal blooms are intensifying in many lakes worldwide based on 30 years of the US’ Geological Survey’s Landsat 5 satellite images (1984 to 2013). These blooms often appear as thick, green goop on or near the surface of a waterbody, and the colour changes in the water can be detected by satellites. The study examined 71 lakes located in 33 countries on 6 continents and discovered that the intensity of summertime algal blooms increased in 48 out of the 71 lakes (68%). The six lakes that experienced the least amount of warming over the 30-year period demonstrated a decrease in bloom intensity. Hence, the findings suggest that warming waters may be a key factor contributing to algal blooms.

In terms of economy, freshwater blooms result in losses of more than $4 billion annually in the US alone. Toxic algal blooms not only affect drinking water supplies, but also aquatic food production, fishing, recreation and tourism. 

The successful control and management of harmful algal blooms is complex and requires the collective efforts of scientists, policy makers and citizens. It is necessary to develop water quality management strategies to account for the interactions between climate change and local hydrological conditions. One of the authors in the Nature study also recommended cutting carbon emissions to prevent freshwater algal blooms. People can further reduce and control the discharge of manure and fertilisers into waters in order to protect our ecosystems and reduce the occurrence of HABs. Additionally, forecasting algal bloom events is important for solving the problems of HABs in drinking water sources by using monitoring tools with satellite technology. Therefore, blooms can be predicted and water treatment plans can prepare accordingly. 

Featured image by: Flickr 

Algae blooms are causing ‘green snow’ along the coastlines of Antarctica and are likely to spread as temperatures rise, according to a study that has created the first large-scale map of the organisms and their movements. 

What is green snow?

The study, published in the Nature Communications journal, used European Space Agency satellite data gathered between 2017 and 2019 as well as on-the-ground observations over two summers in Antarctica’s Ryder Bay, Adelaide Island, the Fildes Peninsula and King George Island, which allowed scientists to map the microscopic algae as they spread across the snow of the Antarctic Peninsula, forming ‘green snow’. 

The data reported is a conservative estimate since it only included green algae. The satellite is only capable of picking up green, which means the data ignored the red and orange algae that accompany it. 

Scientists identified 1 679 separate blooms of green algae on the snow surface, covering an area of 1.9 sq km, equating to a carbon sink of around 479 tons per year. Patches of green snow algae can be found along the coastlines of Antarctica, usually in ‘warmer’ areas, where average temperatures are a little above zero degrees Celsius during the Southern Hemisphere’s summer months of November to February.

Warming temperatures could create environments more favourable for the algae, which need slushy, wet snow to thrive.

Dr Andrew Gray, lead author of the paper, and a researcher at the University of Cambridge, says, “As Antarctica warms, we predict the overall mass of snow algae will increase, as the spread to higher ground will significantly outweigh the loss of small island patches of algae.”

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green snow antarctica
A map showing the areas in Antarctica where the ‘green snow’ is present (Source: Andrew Gray, Monika Krolikowski, Peter Fretwell, Peter Convey, Lloyd S. Peck, Monika Mendelova, Alison G. Smith, Matthew P. Davey. Nature Communications, 2020; 11 (1)).

Dr Gray added that while an increase in snow melt could lead to more algae growing, the distribution of the organisms is heavily linked to bird populations, whose excrement acts as a fertiliser to encourage growth. He says, “As bird- particularly penguin- populations are affected by warming temperatures, the snow algae could lose sources of nutrients to grow.” Over 60% of blooms were found near penguin colonies and others were found near birds’ nesting sites. 

Dr Gray says that an increase in the blooms could also lead to further snow melt. “It’s very dark- a green snow algal bloom will reflect about 80% of the light hitting it, so it will increase the rate of snow melt in a localised area,” he says.

Researchers found that almost two-thirds of the bloom were on small, low-lying islands. The researchers say that as the region warms due to the climate crisis, these islands could lose their summer snow cover and algae- although in terms of mass, the majority of snow algae is found in areas where they can spread to higher ground when snow melts. 

The Antarctic Peninsula is the part of the region that has experienced the most rapid warming in the latter part of the last century, the researchers say.

The region experienced an unprecedented heatwave in the beginning of the year- on February 9, a research station recorded a temperature of 20.75°C, the continent’s first time to exceed 20°C in recorded history.

The algal blooms in Antarctica are equivalent to about the amount of carbon that’s being omitted by 875 000 average UK petrol car journeys. Matthew Davey, one of the researchers of the study says, “That seems a lot but in terms of the global carbon budget, it’s insignificant. It does take up carbon from the atmosphere but it won’t make any serious dent in the amount of carbon dioxide being put in the atmosphere at the moment.” 

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