The Close Relationship Between Algae and Water Quality

Apr 25

Most people are familiar with algae as it comes in the form of seaweeds, pond scum, or algal blooms in lakes. Thus, it can cause some confusion as to their exact description. Algae is more of an umbrella term that includes a wide range of organisms that are capable of producing oxygen through photosynthesis. These organisms don't necessarily need to be related. However, they need to be differentiated from land plants. Though the two are vastly different. Algae lack true roots, stems, leaves, and a vascular system that enables water and nutrients to circulate throughout their bodies. Also, most algae are unicellular while plants are multicellular. Moreover, algae come in a wide variety of forms and sizes. Some algae exist as single microscopic cells, some algae are multicellular and macroscopic, some take on a leafy appearance like seaweeds.

Another thing that complicates algae is the fact that it can include both prokaryotic and eukaryotic organisms. While most algae are eukaryotic, one interesting prokaryotic organism the Cyanobacteria, also known as blue-green algae, is, as the name suggests, algae. It is interesting to note that most eukaryotic organisms that are capable of photosynthesis came into being because their primitive ancestors engulfed cyanobacteria.

In essence, algae refer to a group of bacteria and plants in aquatic environments, and they are important for monitoring water quality. Their short life cycle, rapid reproduction rate, and nutrient needs make them suitable for water quality assessments. Aside from that, algae respond quickly to changes in water chemistry and exhibit this response by changing species composition and density. For example, when acid-forming chemicals would lower the pH of an aquatic environment, the genera of algae would shift favouring those that can tolerate the acidity.

Algae Habitat

With the exemption of single-celled green algae that inhabit moist areas and lichens, most algae live in aquatic environments which are quite diverse and offer unique conditions for the algae. Aquatic environments can either be freshwater or saltwater, both of which can vary greatly with regard to their physical and chemical characteristics. This is why there is a wide variety of algae specialized to survive under various temperatures, oxygen or carbon dioxide concentrations, acidity, and turbidity. The diversity of algae does not stop there for there are algae that live on land. They grow on tree trunks, animal fur, snowbanks, hot springs, soil, and even in desert crusts. They may also exist independently or form symbiotic relationships with other non-photosynthetic organisms like ciliates, sponges, mollusks, and fungi. When they create symbiotic relationships they are able to survive in environments that most of the other members of the group aren’t able to survive.

Nutrition requirements of Algae

Most algae are autotrophs meaning they produce their own food and they do this through photosynthesis. To be more specific, algae are photoautotrophs because they use the light energy from the sun to convert carbon dioxide into carbohydrates and release oxygen as a byproduct. With that said, there are other algal species that obtain their nutrition through different means. Some algal species acquire nutrients from organic materials or are heterotrophic. There are algal species that are osmotrophs, absorb nutrients from dissolved substances, phagotrophs, consume bacteria or other prey, and auxotrophs, organisms that feed on a single essential vitamin and nothing else. Some researchers believe that some algal species are capable of combining photoautotrophy and heterotrophy, an ability known as mixotrophy.

Modes of Reproduction in Algae

Various algal species have different reproductive methods. Some are capable of asexual reproduction, others are capable of sexual reproduction, and some can do both. In algal species that perform asexual reproduction, the process usually involves the production of a motile spore. Algae could also perform mitosis and produce genetically identical offsprings. They could also create offspring through the fragmentation of a colony. Sexual reproduction in algae involves the production of gametes. Their subsequent union creates offspring.

Classifications of Algal Species

Cyanobacteria (Blue-green algae)

The prefix “cyano” in cyanobacteria means blue. This algal species is also referred to as blue-green algae. Their characteristic colours have to do with the fact that their pigments absorb specific wavelengths of light. Phycocyanin is a blue pigment. It absorbs red wavelengths which is why it is coloured blue. Chlorophyll is the green pigment. Some species of cyanobacteria contain the red pigment phycoerythrin. This red pigment absorbs light in the green region of the wavelength spectrum which is why they give off a pink or red colour.

The “bacteria” in cyanobacteria indicates that this alga is a bacterial organism which means it is also a prokaryotic organism, despite the fact that they are capable of producing oxygen through photosynthesis and are capable of living in the same environment as eukaryotic algae. Cyanobacteria are gram-negative bacteria. They are capable of converting atmospheric nitrogen to beneficial forms like ammonia.

Eukaryotic algae

There is no single common ancestor for eukaryotic algae, they are polyphyletic. However, their close similarities lead to the formation of the large group known as algae. Author Fabien Burkilists from the Canadian Institute for Advanced Research offers five supergroups of eukaryotic organisms: Ophiskontha, Amoebozoa, Excavata, Archaeplastida and SAR which is composed of three groups, Stramenopiles, Alveolata and Rhizaria. Algal species fall under the Archaeplastidia supergroup. This supergroup has species like chlorophytes which is a subset of the green algae, charophytes which are freshwater green algae, and glaucocystophytes which are unicellular freshwater algae. However, due to their diversity, some algal species are found distributed amongst the Alveolata, Excavata, Rhizaria and Chromista supergroups.

Importance of Algae

Probably the most important thing about algae is that they produce about half of the oxygen present in the Earth’s atmosphere. But algae has more to offer than just that.

Recent studies have uncovered that a significant portion of petroleum originates from ancient algae deposits, mostly cyanobacteria. The exact identity of these ancient algae is still unknown. Algal deposits that are relatively younger feature eukaryotic marine green algae. These discoveries led researchers to pursue a promising fossil fuel alternative, algal biofuels. All algae can accumulate energy-rich oils within their cells. Some microalgal species are able to accumulate high levels of oil that they can be considered a viable source of biofuel.

When photosynthetic organisms produce oxygen, they will naturally use up the carbon dioxide present in the atmosphere. Since algae are fast producers of oxygen, then they are also great consumers of carbon dioxide. In other words, algae can significantly lower carbon dioxide levels while increasing oxygen levels.

Eutrophication and Algae Bloom

When there is excess sunlight, carbon dioxide, nutrient fertilizers, or any combination of these essential growth factors for photosynthesis, excessive plant and algal growth occur. There are natural processes that lead to the introduction of excess sunlight, carbon dioxide, and nutrients into bodies of water. Among them, Eutrophication or the introduction of excess nutrients is the most common. This natural process occurs naturally over centuries as streams, rivers, and other forms of moving water carry nutrient-rich sediments into water bodies. However, human activities hastened this natural process by introducing large amounts of nutrients, as done in agriculture, into the soil. These nutrient-enriched soil would then be carried by run-off into the lake. Eutrophication has dire consequences on lakes that are used as a drinking water source, for aquaculture, and for recreational purposes. Eutrophication may cause algal blooms that ruin drinking water quality, kill off aquaculture products, and destroy the aesthetic quality of a body of water.

How is it that eutrophication can cause such serious consequences? The answer is dense algal blooms. These algal blooms can impart a foul smell to the water. They can also reduce water clarity and harm water quality. Since algal blooms are capable of reducing water clarity, light penetration is lessened which hampers the growth of plants present in littoral zones. When the reduction of light penetration is severe, plants in the littoral zones die in large numbers. Predators present in this body of water that rely on sight to catch prey may also die off as they become unsuccessful in catching prey. During the day, increased photosynthesis brought about by the increase in the mass of photosynthetic organisms can severely deplete inorganic carbon levels in the water which leads to an extreme rise in pH levels. When the water pH is drastically changed, organisms that rely on chemical cues may have their chemosensory abilities impaired. When these algal organisms die off, the microbial decomposition of their remains consumes dissolved oxygen. When the amount of decaying organic matter is so great, it may suck out most or even all of the oxygen creating hypoxic or anoxic zones. In these zones, organisms that rely on oxygen are essentially suffocated to death. This phenomenon continually threatens commercial and recreational fisheries worldwide.

There are some species of algae that produce toxins such as microcystin and anatoxin-a. When these organisms would explode in numbers, the phenomenon is referred to as harmful algal blooms. They have been associated with the degradation of water quality, destruction of important aquaculture, and public health risks.

Among the members of the algae group, cyanobacteria are most commonly associated with Harmful Algal Blooms. The reason why has to do with cyanobacteria’s ability to dominate over other organisms under high nutrient concentrations, low nitrogen-to-phosphorus ratios, low light, reduced mixing, and high-temperature conditions. Harmful algal blooms caused by cyanobacteria have ruined drinking water systems, and also killed off aquacultural products which led to large financial losses.

Controlling Algal Blooms

Eutrophication and the algal blooms that it generates pose a serious threat to drinking water sources, aquaculture, and recreational water bodies. With that said, something must be done to control their growth. Both government agencies and non-government organizations have worked on legislation to regulate the amount of nutrients introduced into the soil but to no avail. Despite the strict regulations on fertilizer usage, eutrophication and harmful algal blooms are still prevalent. It is projected that eutrophication will only get worse. As the human population increases, food demand increases along with it. This increase in food demand will pressure farmers to produce more to meet the demand. This pressure to meet the food demand will lead to a drastic increase in fertilizer usage. It is imperative that a concrete solution to the eutrophication problem that can account for the growing population be created as soon as possible.

Current strategies to minimize the effects of eutrophication include:

Diversion of Excess Nutrients - diversion of sewage effluent and all other nutrient-rich water so that it doesn’t mix with water bodies or lowering the rate at which nutrient-rich water enters a body of water.
Nutrient Ratio Alteration - changing nitrogen, phosphorus, and silica concentrations.
Physical Mixing - controlling the physical mixing of water to discourage the growth of algae.
Shading Bodies of Water with Opaque Liners or Water-based Stains - reducing the light that enters the water body to reduce photosynthesis.
Usage of potent algaecides and herbicides - directly controlling algae population by using chemicals that are capable of killing them.

Unfortunately, these strategies are ineffective, costly, and impractical. This is especially true for large water bodies with complex ecosystems. Controlling nitrogen and or phosphorus inputs into water bodies can be done through bottom-up control methods. Bottom-up control methods may come in the form of using organisms in the lower levels of the food chain that use up nutrients, out-competing algae for theirs. Despite this, it is still difficult to reduce nutrients that enter into bodies of water that are within close proximity of agricultural areas. The usage of algaecides is effective for reducing harmful algal blooms. However, it’s only a short-term fix. Aside from that, using them to control harmful algae blooms is costly. It doesn’t solve the primary cause of the problem, and they pose health risks to humans, livestock, and wildlife that may come into contact with them. They may also harm other non-target aquatic organisms.

Biomanipulation, or the alteration of a food web to restore ecological balance, is a promising solution to algal blooms. Biomanipulation can be done this way: reduce secondary consumer populations, organisms that prey on zooplankton, by encouraging the increase in tertiary consumer populations, organisms that prey on the secondary consumers. By doing so, you increase the population of zooplanktons and also large-body generalist grazers like Daphnia. Since zooplanktons and other generalist grazers feed on algae, increasing their population this way would lower the population of algae. Another way would be to reduce the population of secondary consumer populations by harvesting them. There are edible planktivorous fishes like salmon. Catching them for their meat would lower their population which increases the population of zooplankton, ultimately decreasing the population of algae. Although studies have consistently shown that fish-centric biomanipulation is effective, its effects are always short-term.

Using algae to treat wastewater

We have established that surface water pollution is one of the most serious environmental problems. This is due to the fact that some of the most important water sources are surface waters.

Organic pollution is one of the largest threats to surface waters. When organic materials are carried off through natural processes towards water bodies, their organic content increases. This occurs naturally, however, human activities have increased the organic content of soil through various methods usually relating to agricultural processes. This, in turn, increases the likelihood of eutrophication and may lead to water quality degradation and algal blooms, which ultimately makes the water body unsuitable for various purposes.

Ironically, the organism that needs to be controlled to prevent algal blooms can also be used to prevent algal blooms. The idea of using algae for treating wastewater goes back to the early 1900s. Researchers noted that algae increased wastewater treatment efficiency. It is in the 1970s that interest in using algae for wastewater treatment spiked. Now, after decades of research, algae have become significant organisms for wastewater treatment for they can remove plant nutrients, heavy metals, pesticides, organic and inorganic toxic substances, and radioactive matter that may be present in the wastewater. It is widely accepted that algal wastewater treatment systems are as effective as conventional treatment systems. Furthermore, algal wastewater treatment systems are considered cost-effective alternatives to conventional wastewater treatment systems.

Algae that are grown from treatment ponds would accumulate nutrients, such as nitrogen and phosphorus, within their body. They could then be used as nitrogen and phosphorus supplements for agricultural purposes. There are also ways to obtain energy from these algae. One of which is the extraction of methane through fermentation.

Another astonishing feature of algae is that they can absorb highly toxic substances such as arsenic, selenium, and zinc. So when they are used for water treatment, they can remove these substances from the water. Aside from arsenic, selenium, and zinc, algae are also capable of removing radioactivity. Realizing how powerful algal wastewater treatment systems are, we could expect that this technology would be developed even further in the future.

Advantages of using Algae in Wastewater Treatment

Algae has an important role in the removal of organic pollutants in water bodies. Studies have revealed that algae are quite effective in removing nutrients, especially nitrogen and phosphorus. As well as harmful substances such as heavy metals, pesticides, and organic and inorganic toxins. The way algae do this is by accumulating them within their cells. 45% to 60% of an algal cell’s dry weight is protein, which contains most of the algal cell’s nitrogen. Phosphorus is another chemical that is found in large amounts within an algal cell. They are essential for the synthesis of nucleic acids, phospholipids, and phosphate esters. Algae has a huge demand for both nitrogen and phosphorus that they are able to suck large quantities of these chemicals from water within hours.

Compared to other treatment systems, oxidation ponds that encourage the growth of certain algal species are just as effective or even better when it comes to nutrient removal. By increasing the amount of dissolved oxygen in water, thereby causing pH to rise, phosphorus sedimentation occurs. The phosphorus is then eliminated, along with ammonia and hydrogen sulphur, with ease. The introduction of dissolved oxygen into the water also acts as a form of pathogen disinfection for the high pH discourages the growth of certain pathogenic microorganisms.

If possible, the usage of a wide range of algal species is highly recommended when it comes to heavy metal removal. Studies have shown that algal species favour certain metals over others, Oscillatoria removes chrome, Chlorellavulgaris removes cadmium, copper, and zinc, Chlamydomonas removes lead, and Scenedesmus removes molybdenum. Algae are not negatively affected by the heavy metals that they accumulate. However, species above them in the food web are not. It is of utmost importance that algae used in wastewater treatment don’t end up in other water bodies as they may damage aquatic ecosystems.

Algae as indicators of water quality

Algae can be thought of as a bioindicator. In other words, algae can be used to identify and qualify the effects of pollutants on the environment. Like any other bioindicator, algae can give us an idea about the cumulative effects of various water pollutants and some estimation of how long the problem has persisted. Algae is considered a good bioindicator because of the following reasons:

Algae are ubiquitous and their large numbers persist for a long time.
Most of the algal species used as bioindicators are present all year round.
Algae are sensitive to pollutants, they react quickly in their presence.
Algae are easy to detect and sample
It is well established that algae are correlated with a certain type of pollution, especially organic pollution