While passing from a water body have you ever noticed a long stretch of green or red colored layer on the surface of the water?
This discoloration of the water is mostly caused due to excessive growth of unicellular microscopic phytoplankton known as algae.
Most of us have heard of algae, but what we don’t know is the degree to which it can affect us.
Algae are photosynthetic eukaryotic organisms that include a wide range of unicellular phytoplankton to multicellular seaweeds, appearing as plant-like structures in the aquatic environment.
With the ability to photosynthesize, algae play a key role in the food chain of marine ecosystems.
Usually consumed by zooplanktons, crustaceans, and small fishes, it forms the base of the food web for aquatic life.
So, where does the problem lie with the presence of algae?
The problem is the accelerated, unintended, and uncontrolled growth of one or more algae in freshwater or seawater ecosystems, known as algal bloom.
The algal blooms can be seen in a variety of colors.
The algae produce these colorful pigments for the purpose of efficient photosynthesis; the density of pigmentation in the algal cell directly determines the color of the algal bloom.
For instance, green color is prominent in green algae due to high chlorophyll content, whereas the accessory pigment known as phycoerythrin is prominent in red algae and produces a spectrum of colours ranging from pink to red.
Similarly the presence of phycocyanin pigment imparts a bluish color to blue green algae, the carotenoid content in almost all algal cells provides it yellowish orange color and fucoxanthin that gives brownish color to brown algae.
Due to its predominant autotrophic (ability to produce its own food) nature, it requires sunlight for its growth; it mostly resides on the upper surface of the water body.
An uncontrolled growth can cover the large surface of the water body, disturbing the marine ecosystem that resides beneath.
How does this happen?
Algae respire and consume the dissolved oxygen present in the water body as well as cut the incident light – both these factors are incredibly important to sustain aquatic life..
An algal bloom can have an algal count of tens of thousands to millions per milliliter.
A small stretch of algal bloom is known as a mini bloom, and a large stretch of algal bloom is known as a macro bloom, having a stretch in kilometers.
All the phytoplankton depend on sunlight for photosynthesis.
When the water surface is covered by algal bloom, most of the photosynthesis will happen at the surface and the penetration of sunlight into the water can be will hindered, there will be limited supply of sunlight for the phytoplankton living in shallow waters affecting the flora of water.
Small fishes, zooplanktons, and crustaceans depend on various planktons for their food, which are then consumed by larger fishes.
Affecting the flora of phytoplankton will disturb the base of the aquatic food chain.
After the process of photosynthesis during the daytime, the algae will require dissolved oxygen for cellular respiration, consuming the surface oxygen.
Also the dead algal cells will start to decompose by microbial action utilizing dissolved oxygen.
Over a period of time, the oxygen produced by the phytoplanktons is not able to cope up with the consumption rate of dissolved oxygen be sufficient enough for to sustain all aquatic life.
Such suffocating conditions may be fatal to various aquatic lives.
The freshwater or seawater algal bloom can cover several kilometers, creating an unfavorable environment for fish to breed.
The marine life around the algal bloom may also bioaccumulate toxins released by algal blooms, which can lead to health risks for birds and humans consuming them.
The growth of algae at the source of water supply can lead to problems with treating of water due to its ability to choke treatment systems.
There can be depleted levels of oxygen in the water, and dead algae could accelerate microbial growth in the water – both unwanted in terms of drinking water supply.
The large mat of filamentous algae can choke the water supply, similarly toxins released by the algal blooms can directly enter human body due to drinking and can be lead person falling sick and even fatal in some cases.
There are several factors that lead to algal bloom.
A combination factors like climatic conditions and man-made activities like excessive nutrient run-offs in contaminated groundwater can trigger the formation of algal blooms.
Blue-green algal blooms have an affinity for the spring season when the temperature is warmer and the increased duration of light.
In tropical regions, warmer water conditions can lead to algal blooms throughout the year.
Temperature conditions above 25 C are favorable for the growth of blue-green algae, which gives them an edge over other algae.
Low temperatures during winter are not favorable for the growth of blue-green algae.
Due to the autotrophic nature of algae, light plays an important role in algal growth. Intermittent high and low-intense light is favorable for the growth of blue-green algae.
Such light conditions can be seen just below the water surface or turbid water.
Also, very high, intense light can lead to the death of algal cells.
Stable Water Flow
Most cyanobacteria prefer stable water conditions with less mixing and higher retention time.
Human activities like building dams, irrigation, and other sources of water consumption reduce the flow rate of the river, providing a favorable environment for algal growth.
Phytoplanktons are capable of generating carbon-containing sugars from photosynthesis, but they also require other nutrients for growth and reproduction.
These nutrients include nitrogen, phosphorus, iron, calcium, etc.
Nitrogen and phosphorus are necessary for all the algae, while other nutrients are required for specific marine plankton.
In deep oceans, the depleted nutrient from the surface is replaced by nutrients from deep nutrient-rich water due to upwelling or from the nutrient-rich coastal runoffs.
Depending on the seasonal conditions and nutrient availability, there are algal blooms that last for a short duration.
But in areas with favorable environments and continuous high concentrations of nutrients, algal bloom can be sustained all throughout the year.
The presence of a large concentration of nutrients in the water ecosystem is known as eutrophication.
Agricultural runoff, stormwater, discharge of sewage water, and other human activities lead to eutrophication, which is the biggest contributor to algal blooms.
Algal blooms are an integral part of the marine ecosystem.
They are oxygen producers, almost half of the oxygen dissolved in the water ecosystem and atmosphere is available as by a product of photosynthesis by phytoplanktons.
However, algal bloom due to eutrophication is the most problematic.
These are slimy green covering mats of microscopic algae attached to each other.
Though such algae are not known to produce toxins, they do possess other dangers to aquatic life, like oxygen depletion, blocking the sunlight, affecting the photosynthesis for other phytoplanktons, and impairing the aesthetics of the water body due to odor and unpleasant sight.
An algal bloom that poses a potential hazard to the health of humans, marine life, and birds due to its toxin production or oxygen depletion causing threat to marine life due high concentration of algal bloom can be classified as a harmful algal bloom.
Some algal species produce toxins that can cause severe harm to human health or even death in some instances.
The toxins produced by algae under normal conditions are broken down due to microbial action, but during an algal bloom the concentration of this toxin produced is very high.
Cyanotoxin is produced by a variety of cyanobacteria, while domoic acid is produced by diatoms, which is a known neurotoxin.
Cyanotoxins are further classified into two categories based on their biological effect.
Like hepatotoxin affecting the liver, microcystin, which affects the kidneys and liver and is a known carcinogen, a neurotoxin affects respiratory muscles and brain activity, dermatotoxins affect the skin, and endotoxins cause inflammation of the gastrointestinal epithelium.
Ingestion of such toxins through drinking water or swimming in such areas can pose the health of a person.
The toxins can also be passed indirectly to humans or birds through the food chain.
The concentration of toxin in increased as the toxins are passed from smaller organisms to next organism in food chain, The shellfish feed by filtering the particles along with phytoplanktons, due to this a concentrated level of toxin is accumulated in it.
When finally the human consumes the fish as food, the toxins are released in the body and impact human health.
In the case of a large algal bloom covering hundreds of kilometers, the water beneath the bloom becomes anoxic due to the decaying process of algal cells by microbial action, reducing the dissolved oxygen content.
Also, the high concentration of algal cells clogs the gills of fish and causes irritation.
Such conditions in an ecosystem lead to suffocation, causing the death of a large population of marine life.
Red tide is a natural phenomenon of marine ecosystems where algal species of diatoms or dinoflagellates form algal bloom during favorable environmental conditions, warm water, and high nutrient availability.
The water is discolored to red as the concentration of diatoms or dinoflagellates reaches 1000 cells per milliliter, and the color intensifies with increased concentration of algal cells.
Diatoms are known to produce a neurotoxin known as domoic acid, which can affect higher vertebrates, birds, and humans.
Even these toxins can reach humans and birds via the food chain, affecting human health.
To avoid further expansion of algal bloom and release of biotoxins into water bodies, it is necessary to control the bloom before it damages the ecosystem and poses health risks for humans and marine life.
There are various methods that can help to control algal bloom.
With this method, the filamentous algal blooms can be removed manually or with the help of machines.
The pumping of surface water that contains most of the algal cells can also help get rid of algal blooms to a great extent.
However, this method for controlling algal bloom is temporary as the remaining cells in the water body can lead to algal bloom over a period of time.
Filtration units are used to separate algal cells and purify drinking water bodies.
The aeration systems help destratify the thermal and light layers in the water body, creating an unfavorable condition for the algal bloom of toxic cyanobacteria.
The greatest disadvantage of this technique is it is not cost-effective, highly time-consuming, and cannot be used to curb algal blooms which are larger in size.
This method to control algal blooms consists of adding chemical additives to water that can precipitate the phosphate from the water.
Many clay and chemical additives such as alum, copper compounds, and chloramines are added in freshwater systems to flocculate and remove algal cells.
Algaecides, usually derived from aquatic herbicides, are used to treat algae, but they are costly and need frequent dosages to check the algal population.
Apart from controlling the algal growth, chemical additives and algaecides can have ill effects on the water ecosystem.
The added chemicals can rupture the algal cells and release harmful toxins into the water body that can cause fatalities of fish and marine life.
These chemicals may also accumulate over time and lead to other unwanted problems in the aquatic ecosystem.
Various biological agents like bacteria, viruses, and parasites have been used to treat algal blooms.
Gymnodinium mikimotoi have been used as algaecide to treat a dinoflagellate species.
Viruses are highly host-specific algaecide, which can effectively target a single species of algae.
However, such a process of biological control of one organism with other organisms can have deleterious effects on natural fauna and can replace the indigenous species with non-indigenous species.
Most of the algal blooms that occur in freshwater or near the sea coast are due to eutrophication by human activities.
To avoid the occurrence of algal blooms, it is preferable to take measures that do not encourage the creation of algal blooms.
The nuisance of HAB disrupting the water body over the years has led to monitoring of water quality that can help to forecast the possible algal bloom development and help strategize plans to tackle them.
Such proactive strategies can help in minimizing health risks and economic impacts due to algal blooms.
Detection of nutrient levels or identifying the presence of HABs from various locations of the water body can help in forecasting the possible algal bloom.
The local and state authorities can work together and design programs for monitoring and containing measures for water management.
Policies should be strictly followed on the usage of fertilizers for agriculture and the discharge of sewage water into the water body.
The landscape modification of regions across fresh water and coastal oceans allows easy nutrient input due to agricultural runoff into the water body, causing eutrophication.
The creation of barriers around the water body can avoid the entry of nutrient-rich water sources into the water ecosystem.
Methods to contain the sources of nutrient runoff like nitrogen and phosphorus from fertilizers should be implemented.
Methods like drip irrigation can help in the focused application of fertilizers, avoiding any traces of nutrients for run-offs.
Implementing wastewater treatment strategies in industries for biological nutrient removal before its discharge into the water bodies can reduce the nutrient concentration into water bodies.
Beneficial bacteria can be used as part of an eco-friendly and natural pond bioremediation strategy for effective lake cleaning products.
The logic behind using these bacteria is simple. Bacteria feed on suspended nutrients and organic sludge in water bodies.
They also utilise nitrates and phosphates for growth, making them unavailable for algae & aquatic plants and naturally curbing eutrophication.
Once the nutrients in the water are reduced, the bacteria become dormant and stop activity.
They naturally activate and multiply once there is an influx of nutrients, and the cycle restarts itself.
The bacteria naturally adapt themselves to the pond ecosystem and reduce the frequency of treatment.
This is why bioremediation strategies remain one of the best options to curb the menace of algal blooms.
