8.5 Eutrophication
5 min read•january 14, 2023
Jillian Holbrook
Jillian Holbrook
is the process by which a body of water becomes enriched in excess dissolved nutrients, typically phosphates and , leading to an overgrowth of aquatic plants and algae.
The ramifications of include: a reduction in dissolved oxygen levels and . Low-oxygen water, also known as hypoxic water, leads to the death of fish and other aquatic organisms, particularly in coastal waterways and estuaries. 🐟
Although can be caused naturally, it is often accelerated by human activities, such as of fertilizers and the discharge of sewage and other wastewater. Excess nutrients can enter from point sources or non-point sources.
Point sources of pollution refer to specific, identifiable sources of pollution from which pollutants are discharged and are, therefore, easier to address. Examples include power plants, , and other industrial discharges. In contrast, non-point sources of pollution refer to diffuse sources of pollution that do not have a single point of origin, such as or stormwater runoff from residential areas, cities, and rural areas. Non-point sources of pollution are more difficult to address and identify.
Effects of Eutrophication
Algal Blooms
When waterways receive too many nutrients, specifically nitrogen and phosphorus, algae can start to overgrow rapidly on the surface of the water, leading to less sunlight entering the water. are a symptom of imbalances within the body of water’s ecology, occurring when the water in question is warm and surrounding weather calm.
Additionally, an overgrowth of algae can cause the water to become cloudy and discolored, making it unattractive for swimming and other recreational activities. The algae can even produce toxins that can be harmful to humans and animals.
When the excess algae or plant matter decomposes, large amounts of carbon dioxide are produced, lowering the pH of seawater, aka., ocean acidification. slows fish and shellfish growth. It also prevents the formation of shells in . Because of these issues, there is less for fishermen to catch, which leads to skyrocketing prices. 🎣
Dead Zones and Fish Kills
are caused by events. A dead zone is an area of a body of water that has low levels of dissolved oxygen due to the decay of plant matter and is unable to support most forms of aquatic life in its . Very few organisms are able to survive in low-oxygen conditions, meaning are void of natural plant and animal life.
Algae of certain types and at high levels, while natural to the aquatic food chain, can produce mass concentrations of toxins that affect other local organisms, sometimes leading to . Between clogging fish gills and lowering dissolved oxygen content, resulting from can decimate fish populations with low oxygen tolerances.
Biodiversity Loss
Unsurprisingly, the aforementioned effects of impact the biodiversity of aquatic ecosystems. In addition to creating that make aquatic environments uninhabitable, the overgrowth of plants and algae can shade out other aquatic plants, creating an additional contribution to . Because organisms in food webs are connected, and aquatic plants provide food and habitat as an , this loss can create an .
Water Chemistry
can also cause changes in the pH, temperature, and other chemical properties of the water, which can be harmful to certain species and affect the overall health of the ecosystem. Chemical imbalances as a result of connect to and , even leading to water unsafe for human consumption or irrigation.
Eutrophic vs Oligotrophic vs Mesotrophic
Eutrophic lakes have high levels of nutrients within the waterways. The lakes are characterized as containing large populations of aquatic organisms, but plants and algae grow to levels that can become a nuisance.
Oligotrophic lakes have low levels of nutrients. They can be characterized as supporting a low level of aquatic organisms. Many can be split into two layers during summer (stratification). The lowest layer is the hypolimnion, which supports cold water organisms due to its low temperature.
Mesotrophic lakes have a moderate amount of nutrients (meso indicates middle). These lakes have occasional algae blooms. If they are deep enough, they can also have hypolimnion, which becomes low oxygen near summer's end, possibly resulting in phosphorus release from the sediments.
Anthropogenic Causes of Eutrophication
Remember that means originating from human activity. 👫
Due to intensive practices of agriculture, industrial activity, and population growth, all of which are factors, have increased. All three of the mentioned processes emit copious amounts of nitrogen and phosphorus. Additionally, activities release two times the nitrogen and three times the phosphorus as naturally occurring emissions.
Regions of the World and Eutrophication
Depending on the region, different levels of nitrogen and phosphorus are emitted:
In developed countries, such as the United States and EU nations, the heavy reliance on animal manure and commercial fertilizers within the agricultural field has led to much . As rain falls, runoff from these fields goes into waterways, raising the levels of nutrients within them. 🐄
Within developing countries, untreated wastewater from sewage and industrial activities are the main contributors to . Additionally, since sewage facilities and factories are less regulated, sometimes the end wastewater is dumped straight into waterways.
Stopping Eutrophication
In estuaries, animals such as reduce nutrients within the water naturally by filtering the water and subsequently feeding on them. Therefore, increasing or re-introducing these organisms into a system can help to stop .
that are designed to capture polluted runoff can catch excess nutrients and/or sediments before they reach more fragile waterways. Or on a more individual level, the public can learn to use fertilizer more wisely by reading and following the manufacturer’s directions, not fertilizing before rainfall, and only fertilizing for nutrient deficiencies. 🌱
Key Terms to Review (22)
Agricultural Runoff
: Agricultural runoff refers to the movement of water containing fertilizers, pesticides, and other chemicals from farmland into nearby bodies of water.Algal Blooms
: Algal blooms are rapid and excessive growths of algae in bodies of water, caused by an excess of nutrients like nitrogen and phosphorus. These blooms can deplete oxygen levels in the water, leading to harmful effects on aquatic life.Anthropogenic
: Anthropogenic refers to environmental changes or processes that are caused by human activities. It includes any impact on the environment resulting from human actions, such as pollution, deforestation, and climate change.Biodiversity Loss
: Biodiversity loss refers to the decline in the variety and abundance of species within a particular habitat or on a global scale. It is primarily caused by human activities such as habitat destruction, pollution, overexploitation, and climate change.Bivalve Mollusks
: Bivalve mollusks are a type of mollusk characterized by having a hinged shell divided into two halves. Examples include clams, oysters, and mussels.Dead Zones
: Dead zones are areas in bodies of water where oxygen levels are extremely low or completely depleted, leading to a lack of aquatic life. These zones often result from excessive nutrient pollution, causing algal blooms that deplete oxygen when they decompose.Ecosystem Cascade
: An ecosystem cascade refers to a series of events that occur within an ecosystem when one change triggers a chain reaction affecting multiple other components. These cascades can have significant impacts on the structure and function of ecosystems.Ecosystem Service
: Ecosystem services are the benefits that humans receive from ecosystems. These services can be categorized into four types: provisioning (e.g., food, water), regulating (e.g., climate regulation, water purification), cultural (e.g., recreation, spiritual value), and supporting (e.g., nutrient cycling, soil formation).Eutrophic Events
: Eutrophic events refer to situations where bodies of water become excessively rich in nutrients, leading to an overgrowth of algae and other aquatic plants. This excessive growth can deplete oxygen levels in the water and harm aquatic life.Eutrophic Lakes
: Eutrophic lakes are bodies of water that have high nutrient concentrations, resulting in excessive plant growth (such as algae) and reduced oxygen levels. These lakes often appear greenish or murky due to algal blooms.Eutrophication
: Eutrophication is the excessive growth of algae and other plants due to an increase in nutrients (such as nitrogen and phosphorus) in a body of water, leading to harmful effects on aquatic ecosystems.Fish Kills
: Fish kills are events where a large number of fish die within a specific area or body of water. These incidents can be caused by various factors such as pollution, disease outbreaks, oxygen depletion, or sudden changes in environmental conditions.Hypoxic Water
: Hypoxic water refers to areas in bodies of water where oxygen levels are extremely low. This can occur as a result of algal blooms consuming oxygen or due to other factors like pollution and nutrient runoff.Mesotrophic Lakes
: Mesotrophic lakes are bodies of water that have a moderate level of nutrients, resulting in a balanced ecosystem with a diverse range of plant and animal life.Nitrates
: Nitrates are chemical compounds made up of nitrogen and oxygen. They are commonly found in fertilizers and can enter water bodies through runoff or leaching. High levels of nitrates in water can lead to pollution and harm aquatic ecosystems.Non-point Source Pollution
: Non-point source pollution refers to the contamination of water, air, or soil that comes from multiple diffuse sources rather than one specific identifiable location.Ocean Acidification
: Ocean acidification occurs when carbon dioxide (CO2) from sources like burning fossil fuels dissolves into seawater and lowers its pH level. This decrease in pH makes seawater more acidic over time, harming marine life such as coral reefs and shellfish.Oligotrophic Lakes
: Oligotrophic lakes are bodies of water that have low nutrient concentrations, resulting in clear and oxygen-rich conditions. These lakes typically support a diverse range of aquatic life, including fish species.Point Source Pollution
: Point source pollution refers to the contamination of water, air, or soil that can be traced back to a specific and identifiable source, such as a factory or sewage treatment plant.Stormwater Facilities
: Stormwater facilities are structures or systems designed to manage and control the flow of stormwater, which is rainwater that runs off from surfaces like roads, parking lots, and rooftops. These facilities help prevent flooding, reduce pollution in water bodies, and recharge groundwater.Wastewater Treatment Plants
: Wastewater treatment plants are facilities that remove pollutants and contaminants from wastewater before it is released back into the environment. They use various physical, chemical, and biological processes to treat the water.Water Chemistry
: Water chemistry refers to the study of the chemical properties and characteristics of water, including its pH level, dissolved oxygen content, nutrient concentrations, and presence of pollutants. It helps scientists understand the quality and health of aquatic ecosystems.8.5 Eutrophication
5 min read•january 14, 2023
Jillian Holbrook
Jillian Holbrook
is the process by which a body of water becomes enriched in excess dissolved nutrients, typically phosphates and , leading to an overgrowth of aquatic plants and algae.
The ramifications of include: a reduction in dissolved oxygen levels and . Low-oxygen water, also known as hypoxic water, leads to the death of fish and other aquatic organisms, particularly in coastal waterways and estuaries. 🐟
Although can be caused naturally, it is often accelerated by human activities, such as of fertilizers and the discharge of sewage and other wastewater. Excess nutrients can enter from point sources or non-point sources.
Point sources of pollution refer to specific, identifiable sources of pollution from which pollutants are discharged and are, therefore, easier to address. Examples include power plants, , and other industrial discharges. In contrast, non-point sources of pollution refer to diffuse sources of pollution that do not have a single point of origin, such as or stormwater runoff from residential areas, cities, and rural areas. Non-point sources of pollution are more difficult to address and identify.
Effects of Eutrophication
Algal Blooms
When waterways receive too many nutrients, specifically nitrogen and phosphorus, algae can start to overgrow rapidly on the surface of the water, leading to less sunlight entering the water. are a symptom of imbalances within the body of water’s ecology, occurring when the water in question is warm and surrounding weather calm.
Additionally, an overgrowth of algae can cause the water to become cloudy and discolored, making it unattractive for swimming and other recreational activities. The algae can even produce toxins that can be harmful to humans and animals.
When the excess algae or plant matter decomposes, large amounts of carbon dioxide are produced, lowering the pH of seawater, aka., ocean acidification. slows fish and shellfish growth. It also prevents the formation of shells in . Because of these issues, there is less for fishermen to catch, which leads to skyrocketing prices. 🎣
Dead Zones and Fish Kills
are caused by events. A dead zone is an area of a body of water that has low levels of dissolved oxygen due to the decay of plant matter and is unable to support most forms of aquatic life in its . Very few organisms are able to survive in low-oxygen conditions, meaning are void of natural plant and animal life.
Algae of certain types and at high levels, while natural to the aquatic food chain, can produce mass concentrations of toxins that affect other local organisms, sometimes leading to . Between clogging fish gills and lowering dissolved oxygen content, resulting from can decimate fish populations with low oxygen tolerances.
Biodiversity Loss
Unsurprisingly, the aforementioned effects of impact the biodiversity of aquatic ecosystems. In addition to creating that make aquatic environments uninhabitable, the overgrowth of plants and algae can shade out other aquatic plants, creating an additional contribution to . Because organisms in food webs are connected, and aquatic plants provide food and habitat as an , this loss can create an .
Water Chemistry
can also cause changes in the pH, temperature, and other chemical properties of the water, which can be harmful to certain species and affect the overall health of the ecosystem. Chemical imbalances as a result of connect to and , even leading to water unsafe for human consumption or irrigation.
Eutrophic vs Oligotrophic vs Mesotrophic
Eutrophic lakes have high levels of nutrients within the waterways. The lakes are characterized as containing large populations of aquatic organisms, but plants and algae grow to levels that can become a nuisance.
Oligotrophic lakes have low levels of nutrients. They can be characterized as supporting a low level of aquatic organisms. Many can be split into two layers during summer (stratification). The lowest layer is the hypolimnion, which supports cold water organisms due to its low temperature.
Mesotrophic lakes have a moderate amount of nutrients (meso indicates middle). These lakes have occasional algae blooms. If they are deep enough, they can also have hypolimnion, which becomes low oxygen near summer's end, possibly resulting in phosphorus release from the sediments.
Anthropogenic Causes of Eutrophication
Remember that means originating from human activity. 👫
Due to intensive practices of agriculture, industrial activity, and population growth, all of which are factors, have increased. All three of the mentioned processes emit copious amounts of nitrogen and phosphorus. Additionally, activities release two times the nitrogen and three times the phosphorus as naturally occurring emissions.
Regions of the World and Eutrophication
Depending on the region, different levels of nitrogen and phosphorus are emitted:
In developed countries, such as the United States and EU nations, the heavy reliance on animal manure and commercial fertilizers within the agricultural field has led to much . As rain falls, runoff from these fields goes into waterways, raising the levels of nutrients within them. 🐄
Within developing countries, untreated wastewater from sewage and industrial activities are the main contributors to . Additionally, since sewage facilities and factories are less regulated, sometimes the end wastewater is dumped straight into waterways.
Stopping Eutrophication
In estuaries, animals such as reduce nutrients within the water naturally by filtering the water and subsequently feeding on them. Therefore, increasing or re-introducing these organisms into a system can help to stop .
that are designed to capture polluted runoff can catch excess nutrients and/or sediments before they reach more fragile waterways. Or on a more individual level, the public can learn to use fertilizer more wisely by reading and following the manufacturer’s directions, not fertilizing before rainfall, and only fertilizing for nutrient deficiencies. 🌱
Key Terms to Review (22)
Agricultural Runoff
: Agricultural runoff refers to the movement of water containing fertilizers, pesticides, and other chemicals from farmland into nearby bodies of water.Algal Blooms
: Algal blooms are rapid and excessive growths of algae in bodies of water, caused by an excess of nutrients like nitrogen and phosphorus. These blooms can deplete oxygen levels in the water, leading to harmful effects on aquatic life.Anthropogenic
: Anthropogenic refers to environmental changes or processes that are caused by human activities. It includes any impact on the environment resulting from human actions, such as pollution, deforestation, and climate change.Biodiversity Loss
: Biodiversity loss refers to the decline in the variety and abundance of species within a particular habitat or on a global scale. It is primarily caused by human activities such as habitat destruction, pollution, overexploitation, and climate change.Bivalve Mollusks
: Bivalve mollusks are a type of mollusk characterized by having a hinged shell divided into two halves. Examples include clams, oysters, and mussels.Dead Zones
: Dead zones are areas in bodies of water where oxygen levels are extremely low or completely depleted, leading to a lack of aquatic life. These zones often result from excessive nutrient pollution, causing algal blooms that deplete oxygen when they decompose.Ecosystem Cascade
: An ecosystem cascade refers to a series of events that occur within an ecosystem when one change triggers a chain reaction affecting multiple other components. These cascades can have significant impacts on the structure and function of ecosystems.Ecosystem Service
: Ecosystem services are the benefits that humans receive from ecosystems. These services can be categorized into four types: provisioning (e.g., food, water), regulating (e.g., climate regulation, water purification), cultural (e.g., recreation, spiritual value), and supporting (e.g., nutrient cycling, soil formation).Eutrophic Events
: Eutrophic events refer to situations where bodies of water become excessively rich in nutrients, leading to an overgrowth of algae and other aquatic plants. This excessive growth can deplete oxygen levels in the water and harm aquatic life.Eutrophic Lakes
: Eutrophic lakes are bodies of water that have high nutrient concentrations, resulting in excessive plant growth (such as algae) and reduced oxygen levels. These lakes often appear greenish or murky due to algal blooms.Eutrophication
: Eutrophication is the excessive growth of algae and other plants due to an increase in nutrients (such as nitrogen and phosphorus) in a body of water, leading to harmful effects on aquatic ecosystems.Fish Kills
: Fish kills are events where a large number of fish die within a specific area or body of water. These incidents can be caused by various factors such as pollution, disease outbreaks, oxygen depletion, or sudden changes in environmental conditions.Hypoxic Water
: Hypoxic water refers to areas in bodies of water where oxygen levels are extremely low. This can occur as a result of algal blooms consuming oxygen or due to other factors like pollution and nutrient runoff.Mesotrophic Lakes
: Mesotrophic lakes are bodies of water that have a moderate level of nutrients, resulting in a balanced ecosystem with a diverse range of plant and animal life.Nitrates
: Nitrates are chemical compounds made up of nitrogen and oxygen. They are commonly found in fertilizers and can enter water bodies through runoff or leaching. High levels of nitrates in water can lead to pollution and harm aquatic ecosystems.Non-point Source Pollution
: Non-point source pollution refers to the contamination of water, air, or soil that comes from multiple diffuse sources rather than one specific identifiable location.Ocean Acidification
: Ocean acidification occurs when carbon dioxide (CO2) from sources like burning fossil fuels dissolves into seawater and lowers its pH level. This decrease in pH makes seawater more acidic over time, harming marine life such as coral reefs and shellfish.Oligotrophic Lakes
: Oligotrophic lakes are bodies of water that have low nutrient concentrations, resulting in clear and oxygen-rich conditions. These lakes typically support a diverse range of aquatic life, including fish species.Point Source Pollution
: Point source pollution refers to the contamination of water, air, or soil that can be traced back to a specific and identifiable source, such as a factory or sewage treatment plant.Stormwater Facilities
: Stormwater facilities are structures or systems designed to manage and control the flow of stormwater, which is rainwater that runs off from surfaces like roads, parking lots, and rooftops. These facilities help prevent flooding, reduce pollution in water bodies, and recharge groundwater.Wastewater Treatment Plants
: Wastewater treatment plants are facilities that remove pollutants and contaminants from wastewater before it is released back into the environment. They use various physical, chemical, and biological processes to treat the water.Water Chemistry
: Water chemistry refers to the study of the chemical properties and characteristics of water, including its pH level, dissolved oxygen content, nutrient concentrations, and presence of pollutants. It helps scientists understand the quality and health of aquatic ecosystems.
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