Kiera Jefferson
Algal blooms are a common occurrence in polluted bodies of water. Nutrient pollution, caused by an excess of nutrients such as nitrogen and phosphorus, acts as a fertiliser for algae, causing rapid growth and resulting in algal blooms. These blooms can have detrimental effects on aquatic life, human health, and the economy. The decomposition of algae consumes oxygen, creating 'dead zones' where aquatic life cannot survive. Additionally, algal blooms can contaminate drinking water, leading to illnesses in both humans and animals. Climate change is believed to be a contributing factor to the increasing frequency and occurrence of algal blooms, with warmer water temperatures and increased polluted runoff from urban areas. Understanding and addressing the factors that contribute to algal blooms are crucial for maintaining the health of aquatic ecosystems and ensuring safe drinking water for nearby communities.
| Characteristics | Values |
|---|---|
| Algae as indicators of water pollution | Algae can be used to indicate water pollution, with a pollution index value of 1-6 assigned to them |
| Algal blooms | Excess nitrogen and phosphorus cause an overgrowth of algae in a short period of time, also called algal blooms |
| Oxygen consumption | The overgrowth of algae consumes oxygen, causing aquatic life to suffocate and die |
| Sunlight blockage | Algal blooms block sunlight from reaching underwater plants |
| Eutrophication | When a waterway becomes overly polluted with nutrients, it undergoes eutrophication, leading to dead zones |
| Toxin release | Harmful algal blooms release toxins that contaminate drinking water, causing illnesses and even death in animals and humans |
| Nutrient pollution sources | Nutrient pollution enters waterways through agricultural and urban runoff, sewage discharges, detergents, manure, and industrial processes |
| Climate change impact | Climate change is increasing the frequency and occurrence of algal blooms due to warming water temperatures, drought, and increased flooding |
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What You'll Learn
Algae can be an indicator of water pollution
Algae are a vital group of bacteria and plants in aquatic ecosystems. They are a significant component of biological monitoring programs for assessing water quality. Algae are ideally suited for water quality assessment because of their nutrient requirements, rapid reproduction rate, and very short life cycle. They are also easily cultured in the laboratory, and sampling is easy, inexpensive, and creates minimal impact on resident biota.
Algae are important indicators of the environment since they respond immediately to both qualitative and quantitative changes in the composition of species in a wide range of water situations. Algal communities are sensitive to changes in their habitat, and the total biomass of algae and many algae species are used as indicators of water quality. Algae communities give more knowledge of variations in water quality than nutrient or chlorophyll-a values.
The formation of algae is related to the tolerance class (ecological optimum) due to abiotic limiting factors of the ecosystem and the biotic interactions among algae. Algae composition and temporal variation in abundances are important in determining the trophic level of lakes. The altitude of lakes will also affect the algal diversity depending on oxygen saturation changes.
Algae can be used to indicate clean and polluted waters. For example, cyanobacteria blooms usually occur when the N:P ratio is low, with phosphorus as the limiting factor for their growth and reproduction. In contrast, when N:P ratios are high, chlorophytes (green algae and flagellates), along with diatoms, are often the dominant genera. This group of algae thrives in organically polluted waters rich in nitrogen and phosphorus and is used as a biological indicator of organic pollution.
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Excess nitrogen and phosphorus cause algae blooms
Algal blooms are a result of excess nutrients from fertilizer, wastewater, and stormwater runoff, coinciding with sunlight, warm temperatures, and shallow, slow-flowing water. An algal bloom is a rapid increase in the density of algae in an aquatic system. While algal blooms sometimes occur naturally, their frequency, duration, and intensity are increased by nutrient pollution.
Nitrogen and phosphorus are essential for the growth of algae and aquatic plants, which provide food and habitat for fish, shellfish, and smaller animals that live in water. However, when there is too much nitrogen and phosphorus in the water, it causes algae to grow faster than ecosystems can handle. This growth leads to harmful algal blooms, or HABs.
Sources of nitrogen and phosphorus include animal manure and chemical fertilizers used in agriculture, as well as fertilizers, yard and pet waste, soaps, and detergents used in and around homes. These sources can be washed into waterways by rain events. Nutrient pollution can also enter waterways from point sources such as industrial and wastewater treatment plant discharges, and nonpoint sources such as septic tanks and stormwater runoff from urban areas, farms, and residential areas.
The overabundance of nitrogen and phosphorus causes an overgrowth of algae, which consumes oxygen and blocks sunlight from underwater plants. When the algae die, the oxygen in the water is further depleted, making it impossible for aquatic life to survive. This leads to "dead zones" where aquatic life cannot survive due to low oxygen levels.
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Algae blooms can be toxic to humans and animals
Algal blooms are the rapid growth of algae or cyanobacteria in water that can harm people, animals, or the environment. While not all algal blooms are harmful, some produce toxins (poisons) that can make people and animals sick. These toxins can be in the cells of the algae or released into the water. People and animals get sick when they come into contact with toxins through water or food.
The growth of harmful algal blooms is influenced by various factors, including nutrient levels, water conditions, and changes in the local ecology. Excessive levels of nitrogen and phosphorus contribute to the development of algal blooms. These nutrients can originate from sources such as agricultural runoff, sewage discharges, and detergents containing phosphorus. When present in high concentrations, these nutrients promote the rapid proliferation of algae, leading to blooms.
The presence of algal blooms can have detrimental effects on aquatic ecosystems. As the blooms proliferate, they consume oxygen and block sunlight from reaching underwater plants, negatively impacting the survival of other aquatic organisms. Additionally, dense blooms can physically clog the gills of fish, shellfish, and other animals, impeding their breathing. When the blooms eventually die off, the decay process further depletes the oxygen levels in the water, creating "dead zones" where aquatic life cannot survive due to oxygen deprivation.
The toxins produced by harmful algal blooms pose a significant threat to both human and animal health. Exposure to these toxins can lead to a range of symptoms in humans, including skin, eye, and throat irritation, vomiting, organ damage, neurological issues, and respiratory problems. Animals can also be adversely affected by ingesting contaminated water or eating fish containing toxic cyanobacteria. Pets, in particular, are highly vulnerable and have been reported to suffer severe health consequences, including death, after consuming contaminated water or coming into contact with toxic algae.
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Algae blooms can be mistaken for sewage
Algal blooms are a natural part of water ecology. They occur naturally in seas, rivers, and lakes. However, they can sometimes be mistaken for sewage or other forms of pollution. This is because algal blooms can be brown and smelly, much like sewage.
During the summer, it is common for large blooms of naturally occurring algae to appear. When the bloom breaks down, as the algae die, a creamy brown-coloured foam can be formed. This foam can persist for a day or two until it is washed away by the rain or tide. It can also be white in appearance, depending on whether there is any sediment trapped in the foam.
The algal bloom can also create an unpleasant odour, often like rotten vegetables or a musty smell, which can be mistaken for sewage. This occurs especially in warm weather.
There are some ways to tell the difference between an algal bloom and sewage. Algal blooms generally occur between April and August. Long lines of algal foam can often be seen off headlands lying parallel to the coast. In rough conditions, thick mats of foam may be created on the shoreline by wave action. Stormwater overflows tend to cause a grey discolouration of the water and often have an origin such as a pipe or outfall, where the discolouration is strongest. Sewage discharges can contain fats and oils, causing waves to flatten around them and sometimes attract flocks of seabirds.
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Algae blooms can cause fish kills
Algal blooms are caused by phytoplankton, free-floating microscopic algae found in both marine and freshwater ecosystems. They form the base of the aquatic food chain and are an essential nutrient for filter-feeding bivalve shellfish and the larvae of commercially important crustaceans and finfish. However, they can also have devastating impacts on local ecosystems, causing mortality and sickness in organisms across multiple trophic levels.
Algal blooms can cause fish kills in several ways. Firstly, they can deplete oxygen in the water due to the high respiration rate of the algae, or by bacterial respiration during their decay, resulting in hypoxic or anoxic conditions that are deadly to fish and other organisms. This can occur during the bloom or after it has terminated. Some algae can also cause physical damage to the gills of fish, impairing their ability to take in oxygen.
In addition, fish can be killed by direct exposure to algal toxins in the water or by consuming prey that contain these toxins. These toxins can enter the food chain when larval fish consume toxic algae, and organisms that consume these fish can also experience toxicity and pass it on to higher trophic levels. Toxins produced by certain algal species, such as Alexandrium and Karenia brevis, have been linked to extensive fish kills and wildlife mortalities. For example, a bloom of Chrysochromulina leadbeateri in Norway killed around 8 million fish in ocean net pens, and blooms of Karenia brevis have caused massive and widespread fish kills in Florida's Gulf coast, with toxins remaining in the water even after the algal cells have died.
The economic impact of algal blooms can be significant, affecting tourism, recreation, and seafood industries. For instance, golden algal blooms in Possum Kingdom Lake, Texas, resulted in fish kills and unsightly foam, reducing recreational fishing and impacting tourism revenue. Similarly, a toxic bloom of Pseudo-nitzschia on the US West Coast shut down the Dungeness crab and razor clam fisheries in 2015, causing a loss of $97.5 million in landings.
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Frequently asked questions
Algae is a natural part of underwater ecosystems, but when nutrients like nitrogen and phosphorus enter waterways in excess, they act as fertilisers and promote the growth of algae and bacteria. This is known as nutrient pollution and can be caused by agricultural runoff, leaked waste from animal feedlots, stormwater runoff, and discharges from wastewater treatment facilities.
Nutrient pollution causes an overgrowth of algae in a short period of time, also known as algae blooms. The N:P ratio determines which algae genera are dominant, with cyanobacteria blooms occurring when the ratio is low, and chlorophytes (green algae) and diatoms being dominant when the ratio is high.
Algae blooms can cause thick, green muck that impacts clear water, recreation, businesses, and property values. They also consume oxygen and block sunlight from underwater plants, creating \"dead zones\" where aquatic life cannot survive due to low oxygen levels. Additionally, harmful algae blooms release toxins that can contaminate drinking water and cause illnesses in humans and animals.
To reduce the occurrence of algae blooms, it is essential to address the sources of nutrient pollution. This includes implementing better regulations and practices to reduce agricultural runoff, improving wastewater treatment processes, and mitigating the impacts of climate change, such as increased water temperatures and flooding, which contribute to polluted runoff in urban areas.
