- Using satellite data, researchers have created a pan-India map of harmful algal blooms caused by cyanobacteria in Indian inland waterbodies.
- An analysis of six Indian waterbodies showed that these blooms were most severe post-monsoon season when nutrient concentrations are the highest.
- The researchers have developed a new tool which will assist water resource managers to monitor water quality and aid decision-making.
Harmful algal blooms in freshwater and marine environments caused by cyanobacteria — microscopic organisms also known as blue-green algae — can threaten ecosystem services leading to poor water quality, fish kills, animal deaths and economic losses. Early detection of harmful algal blooms could enable swift action to prevent aquatic, environmental and health hazards.
Now, researchers have developed a novel interactive cloud-based dashboard called “CyanoKhoj” in the Google Earth Engine, using satellite data, to monitor harmful algal blooms in Indian inland waterbodies, as an early warning system. CyanoKhoj is derived from the term meaning “search for cyanobacteria” in Hindi.
Capable of near-real-time monitoring, CyanoKhoj is an open-source tool that can be used for global waterbodies, state the researchers. Available as a user-friendly web app, users can access it with a browser and Internet connection on their computer or smartphone.
“This app can be used by water managers to constantly keep an eye on target waterbodies for any ongoing or potential Cyanobacterial Harmful Algal Blooms (CyanoHABs) and take water quality and water management decisions accordingly,” said lead author Chintan B. Maniyar, a doctoral student at the University of Georgia, U.S.A. “This app can save a lot of resources and effort typically allocated to field trips and manual field sampling,” he pointed out, adding that this tool also enables monitoring inaccessible waterbodies.
Before visiting a waterbody for any recreational activity, people can use CyanoKhoj, Maniyar suggested. “One can just pull up the waterbody and check if there has been any CyanoHAB activity lately. If there has, it is not safe to go there.”
While the study was based in India, CyanoKhoj can be used in waterbodies around the world, said Maniyar, adding that it can elicit awareness of freshwater quality in developing countries.
“Just like CyanoKhoj is developed for India, we plan to develop a dedicated water quality platform for other nations, after validating the tool using field data from those geographic locations,” said Deepak Mishra, professor and associate head at the University of Georgia and a co-author of the study.
Punyasloke Bhadury, a microbial ecologist who was not associated with the study, said, “This unique approach of CyanoKhoj and using robust satellite data expands the scope to monitor harmful algal blooms more effectively from space.”
Bhadury, a professor at the Indian Institute of Science Education and Research – Kolkata (IISER-Kolkata), added that the “study shows how technology can be effectively integrated for achieving healthy aquatic ecosystems and human welfare and ultimately pave the way for citizen science in tracking harmful algal bloom across aquatic ecosystems.”
Algal blooms and climate change
An algae bloom refers to rapid growth of a large mass of microscopic marine algae referred to as phytoplankton. Blooms are mainly caused by nutrient pollution — often nitrogen or phosphorus — from agricultural fertiliser runoff, untreated sewage discharge or industrial wastewater entering into the sea or into lakes, for example. As microbes degrade algae, they use up oxygen in the water causing hypoxia (low oxygen conditions) that leads to fish deaths and ecosystem-wide consequences.
In India, many people rely on inland waterbodies for their livelihoods such as fishing and agriculture or domestic activities such as bathing, cooking, and spiritual rituals. CyanoHABs can affect livelihoods and exposure to toxins produced by cyanobacteria also pose a health threat, not only for humans but also for birds and other animals such as cattle that drink from waterbodies.
“While there are a lot of new initiatives focused on cleaning rivers and better managing waters, there is very little awareness of such CyanoHABs and their extreme health implications in humans and animals. It is necessary to raise awareness about CyanoHABs and their implications and have a robust infrastructure to monitor Indian waters,” the researchers stressed.
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CyanoHABs have increased on a global scale over the past decades. Scientists expect that blooms in lakes enriched with minerals and nutrients would further rise in occurrence, intensity and duration with global warming and rising atmospheric carbon dioxide concentrations. The effects of climate change on cyanobacteria are complex and more research is needed to elucidate the responses of cyanobacteria to warming.
“Given the coastal oceans of South Asia, in particular, Indian coastlines are reeling from climate change and other anthropogenic factors therefore incidents of harmful algal blooms are expected to substantially increase, which would have long-term adverse consequences on many of the vulnerable coastal biotopes and linked blue economy,” said Bhadury of IISER-Kolkata.
As part of a pan-institutional project, Bhadury’s research group monitored the Sundarbans mangrove system in the Bay of Bengal and found initial trends of a number of harmful algal bloom events. “Our studies have shown that the warming of the Bay of Bengal can be a crucial factor that could have long-term consequences on the occurrence of harmful algal blooms in the coastal Bay of Bengal,” he revealed.
Country-wide CyanoHABs map
“CyanoHABs are dominated by a distinct photosynthetic light-absorbing pigment called Phyocyanin (PC), which is not present in other algae blooms. PC strongly absorbs the orange color (620 nm) of incoming solar radiation,” explained Abhishek Kumar, coauthor of the study and a postdoctoral research associate at the University of Massachusetts. “We used this fact to detect the presence of cyanobacteria in inland lakes and reservoirs and differentiate CyanoHABs from other non-toxic green algae blooms.”
The severity of blooms can be quantified by using the relationship between the absorption of orange light and laboratory-based cyanobacteria cell density measurements, Kumar added.
Using robust cyanobacteria remote sensing algorithms, the team created the first-ever pan-India CyanoHAB map using European Space Agency’s Sentinel 3-Ocean and Land Colour Instrument (OLCI) satellite data.
The researchers demonstrated the use of CyanoKhoj on selected lakes and reservoirs spread across five states with different climatic regions: Bargi and Gandhisagar Dams in Madhya Pradesh, Hirakud Reservoir in Odisha, Ukai Dam in Gujarat, Linganamakki Reservoir in Karnataka and Pulicat Lake in Tamil Nadu. For these waterbodies, the team performed a spatio-temporal analysis for 2018 to observe the timing, duration and intensity of CyanoHABs.
“We indeed observed strong CyanoHAB presence in all six waterbodies and were able to see their spatial variation in each of the waterbodies across time,” said Maniyar. CyanoHABs occurred mostly in nutrient-rich waterbodies that were prone to industrial and other nutrient-rich discharges.
In addition, the team analysed the presence of CyanoHABs from 2016 to 2020 for all six waterbodies. The findings showed that blooms were most severe post-monsoon season when nutrient concentrations in the waterbodies are at a peak and they decline towards winter.
“We targeted specific waterbodies to showcase the advanced capabilities of the tool, but keep in mind that this tool was used to map all the waterbodies in the country that the Sentinel-3 satellite could resolve,” Maniyar points out. To view a waterbody, simply drag to it. In the near future, the team will prepare an exhaustive list of Indian waterbodies in the drop-down list for easier navigation.
Maniyar, C. B., Kumar, A., & Mishra, D. R. (2022). Continuous and Synoptic Assessment of Indian Inland Waters for Harmful Algae Blooms. Harmful Algae, 111, 102160.
Banner image: Bloom of cyanobacteria in a freshwater pond. Photo by Christian Fischer/Wikimedia Commons