Climate change has been occurring naturally as well as caused by anthropogenic activities over the decades. In relation to the fresh and marine water, the concentration of greenhouse gases results in temperature rise of surface water, lower pH and changes to precipitation, evaporation and vertical mixing of water. All these consequences of changing the environment in combination with excessive level of nutrients are potentially contributing to harmful algal blooms (HABs) in many different water bodies.
Records of the lake algae fossils could be used to detect climate change in the past. However, this paper will focus on the effect of climate change on HABs, more specifically blue-green algae also known as cyanobacteria.
The ability of cyanobacteria to response to environmental conditions associated to climate change has been documented since the first occurrence of cyanobacteria around 3.5 million years ago. Thus, looking into the evolutionary history, cyanobacteria has been adapted to extreme conditions such as temperature fluctuation, exposure to high UV radiation, abundance and scarcity of nutrients.
Cyanobacteria harmful algal blooms (CHABs) cause toxins to increase in the water used for drinking, tourism and recreation, spiritual purposes, agriculture, and the natural habitat for various animal species; therefore, CHABs affect many different stakeholders and industries. In addition, considering all consequences, CHABs may have a great impact on the economy.
The most important CHABs are caused by certain species from the genera Anabaena, Microcystis and Aphanizomenon. Indeed, producing cyanotoxins is the most intriguing feature of these species. The presence of different types of cyanotoxins in recreational or drinking water could affect different organs: hepatotoxins (liver), neurotoxins (nervous system) and dermatoxins (skin) if contact with water, eating contaminated fish, drinking or inhaling contaminated water occurs.
Generally, toxins produced during an algae bloom cycle are harmful to human, animals and environment.
Additionally, changing precipitation patterns, melting glaciers and intensifying storms result in the escalation of nutrient’s input and promote eutrophication. Eutrophication is a process induced by increased nutrients, especially nitrogen and phosphorus, in water bodies resulting in growth of algae and plants. This phenomenon could take place naturally, but the anthropogenic input of nutrients, also called cultural eutrophication, is considered as a major factor. Thus, fertilization of arable land, sewage discharging, industrial effluents, use of detergents, extensive livestock farming are some of the activities that are responsible for the anthropogenic input of nutrients.
Regardless, the increased availability of nutrients is causing changes of lakes from oligotrophic which are cold, low in nutrients and clear through mesotrophic to eutrophic, nutrient-enriched lakes. Some of the examples are Lake Mälleran – Sweden; Lake Biwa – Japan; Lake Constance between Germany, Switzerland and Austria; Lake Balaton – Hungary; Lake Taihu – China; the Great Lakes in North America and many others.
The combination of circumstances such as high water temperature conditions and rising nutrient levels lead to increased numbers of algae populations (stimulates algal bloom).
How big is the problem
Nowadays the visible signs of global climate change are evidenced in the numerous massive algal bloom events we are observing worldwide driven by warm water conditions. Hence, NASA joins the efforts of identifying and recording the algal bloom events. Satellite images show that the extent of algal bloom in the oceans and lakes has been exceeding expectations, an example, August 2015 the Baltic Sea toxic blooms of cyanobacteria accelerated by warm sea temperature.
Drinking water supplies have also been at risk in the past years, not only facing taste and odour problems but also resulting in public health issues.
In such a way, Toledo, Ohio shut down the water supply service to 500,000 people last year during the algal bloom; Thirty-five million dollars has been spent this year to fight algal bloom in Chaohu Lake, the fifth largest freshwater lake in China which is struggling to supply local residents with potable water; Indian Lake (USA) was closed the whole last summer due to blue-green algae.
However, an innovative approach without creating another consequence or contributing to the increase in frequency, extent and duration of HABs that are possibly related to climate change, is needed in order to address the problem in an environmentally friendly way. Besides this, water monitoring is a very important measure to predict algal blooms.
High costs are mostly related to chemical treatments, usually copper sulphate as the most popular method of treatment that requires frequent dosing. On the other hand, it further affects other aquatic organisms and ecosystems.
Indeed, using a renewable energy source, this chemical-free technology controls only algae without affecting fish, plants or other aquatic life and does not result in the release of additional pollutants that could contribute to climate change.