How can agriculture lead to utrophication and fish kills


Agricultural runoff, sewage, surface runoff, chemical spills and hazardous waste spills can all potentially lead to water toxicity and fish kill. Some algae species also produce toxins. In Florida, these include Aphanizomenon, Anabaena and Microcystis.

High levels of nitrogen and phosphorus can cause eutrophication of water bodies. Eutrophication can lead to hypoxia (“dead zones”), causing fish kills and a decrease in aquatic life.Nov 4, 2021


How does eutrophication cause fish to die?

How does eutrophication cause fish kills? One of the negative impacts of eutrophication and increased algal growth is a loss of available oxygen, known as anoxia. These anoxic conditions can kill fish and other aquatic organisms such as amphibians.

What are the causes of fish kills?

Water Q&A: What causes fish kills? Completed Find out more about the causes of fish kills, including dissolved oxygen and toxins. What causes fish kills? Sources/Usage: Public Domain. Many, but not all, fish kills in the summer result from low concentrations of dissolved oxygen in the water.

What are the negative effects of fish farming?

According to the World Health Organization, the consumption of dioxins can cause reproductive and developmental problems, damage the immune system, interfere with hormones and also cause cancer. There are a number of ways that fish farming negatively impacts its local environment.

Does Agri-agriculture impact on eutrophication risk?

Agriculture’s impact on eutrophication risk may also be overestimated in many catchments, and more accurate accounting of sources, their bioavailabilities and lag times is needed to direct proportioned mitigation efforts more effectively.


How does agricultural runoff affect fish?

As algae dies it decomposes, and the business of decomposition requires a lot of oxygen. All that oxygen consumption leads to hypoxia, the absence of dissolved oxygen in water, which causes sportfish such as trout and salmon to literally suffocate.

How does over fertilizing lead to eutrophication?

Large-scale farmers also use fertilizers to grow produce and other crops needed to feed a rapidly increasing population. Fertilizer nutrients left unused in soil can run off into coastal waters, lakes and streams, resulting in eutrophication, or the addition of excessive amounts of nutrients.

Can eutrophication be caused by fertilizers?

Excess nitrogen from the fertilizers can cause eutrophication in the ocean, which can lead to harmful algae blooms or hypoxia — reduced levels of oxygen that create conditions in which organisms can’t survive.

What are the reasons for eutrophication?

Water eutrophication is mainly caused by excessive loading of nutrients into water bodies like N and P. Excessive nutrients come from both point pollution such as waste water from industry and municipal sewage, and non-point pollution like irrigation water, surface run water containing fertilizer from farmland, etc.

How do fertilizers affect aquatic organisms?

When manure or commercial fertilizers enter surface water, the nutrients they release stimulate microorganism growth. The growth and reproduction of microorganisms reduce the dissolved oxygen content of the water body. Without sufficient dissolved oxygen in surface water, fish and other aquatic species suffocate.

How can fertilizer harm the ocean?

Commercial fertilizers release nutrients as they enter surface water. These nutrients stimulate microorganism growth and reproduction, reducing the dissolved oxygen found in marine ecosystems. Fish and other aquatic species suffocate when their habitat doesn’t have enough dissolved oxygen in surface water.

How does agriculture pollute water?

Agriculture as a water polluter: cause Pesticides and fertilizers used in agriculture can contaminate both groundwater and surface water, as can organic livestock wastes, antibiotics, silage effluents, and processing wastes from plantation crops.

What is eutrophication in agriculture?

An overabundance of nutrients—primarily nitrogen and phosphorus—in water starts a process called eutrophication. Algae feed on the nutrients, growing, spreading, and turning the water green.

How does agriculture affect water quality?

Excessive irrigation can affect water quality by causing erosion, transporting nutrients, pesticides, and heavy metals, or decreasing the amount of water that flows naturally in streams and rivers.

What are some agricultural practices that caused eutrophication?

Eutrophication is predominantly caused by human actions due to their dependence on using nitrate and phosphate fertilizers. Agricultural practices and the use of fertilizers on lawns, golf courses and other fields contribute to phosphate and nitrate nutrient accumulation.

What are the two major causes of eutrophication?

Nutrient pollution, a form of water pollution, is a primary cause of eutrophication of surface waters, in which excess nutrients, usually nitrogen or phosphorus, stimulate algal and aquatic plant growth. A common visible effect of eutrophication is algal blooms.

How eutrophication effects aquatic plants and animals?

Eutrophication accelerates algal growth and reduce the oxygen level in the environment. Some times the sudden algal blooms toxic to the environment and kill the organisms in the environment including fishes. The similar impact also noticed if oxygen level is low.

What is the NOAA model?

The NOAA scientists used aquaculture modeling tools to demonstrate that shellfish aquaculture compares favorably to existing nutrient management strategies in terms of efficiency of nutrient removal and implementation cost.

How does acidification affect fish?

Acidification slows the growth of fish and shellfish and can prevent shell formation in bivalve mollusks. This leads to a reduced catch for commercial and recreational fisheries, meaning smaller harvests and more expensive seafood.

How does eutrophication affect the ocean?

Eutrophication sets off a chain reaction in the ecosystem, starting with an overabundance of algae and plant s. The excess algae and plant matter eventually decompose, producing large amounts of carbon dioxide. This lowers the pH of seawater, a process known as ocean acidification.

What are the effects of excess nutrients on seagrass?

Excessive nutrients lead to algal blooms and low-oxygen (hypoxic) waters that can kill fish and seagrass and reduce essential fish habitats. Many of these estuaries also support bivalve mollusk populations (e.g., oysters, clams, scallops), which naturally reduce nutrients through their filter-feeding activities.

What is the term for the process of eutrophication?

Eutrophication is a big word that describes a big problem in the nation’s estuaries. Harmful algal blooms, dead zones, and fish kills are the results of a process called eutrophication — which occurs when the environment becomes enriched with nutrients, increasing the amount of plant and algae growth to estuaries and coastal waters.

How much did Cuomo spend on Long Island?

In September 2017, New York Governor Andrew M. Cuomo announced a $10.4 million effort to improve Long Island’s water quality and bolster the economies and resiliency of coastal communities by restoring native shellfish populations to coastal waters.

Is oyster harvesting part of nutrient management?

In Chesapeake Bay, for example, nutrient removal policies include the harvesting of oyster tissue as an approved method, and in Mashpee Bay, Massachusetts, cultivation and harvest of oysters and clams are part of the official nutrient management plan.


Eutrophication is characterized by excessive plant and algal growth due to the increased availability of one or more limiting growth factors needed for photosynthesis (Schindler 2006), such as sunlight, carbon dioxide, and nutrient fertilizers.


The most conspicuous effect of cultural eutrophication is the creation of dense blooms of noxious, foul-smelling phytoplankton that reduce water clarity and harm water quality (Figure 2).


Given the widespread extent of water quality degradation associated with nutrient enrichment, eutrophication has and continues to pose a serious threat to potable drinking water sources, fisheries, and recreational water bodies.


Despite dramatic improvements in water quality as a result of large-scale efforts to reduce nutrient enrichment (e.g., Clean Water and Safe Drinking Water Acts in the 1970s), cultural eutrophication and concomitant HABs continue to be the leading cause of water pollution for many freshwater and coastal marine ecosystems and are a rapidly growing problem in the developing world (Smith & Schindler 2009).

References and Recommended Reading

Arend, K. K. et al. Seasonal and interannual effects of hypoxia on fish habitat quality in central Lake Erie. Freshwater Biology 56, 366-383 (2011).

What is the term for the condition where the oxygen concentrations of a body of water are low?

Eutrophication occurs in a body of water when an increase of mineral and organic nutrients has reduced the dissolved oxygen,… Commonly, culturally eutrophic aquatic systems may exhibit extremely low oxygen concentrations in bottom waters, a condition known as hypoxia.

What are the effects of eutrophication on the Black Sea?

In the Black Sea and elsewhere, hypoxic waters from cultural eutrophication have resulted in massive fish kills, with rippling effects throughout the food chain and local economies . Coastal marine systems also may be affected by this process.

How does cultural eutrophication affect the environment?

Cultural eutrophication occurs when human water pollution speeds up the aging process by introducing sewage, detergents, fertilizers, and other nutrient sources into the ecosystem. Cultural eutrophication has had dramatic consequences on freshwater resources, fisheries, and recreational bodies of water and is one of the leading causes …

What are the problems with nitrogen?

Nitrogen from municipal sewage treatment plants and the direct runoff from animal feedlots are serious problems in many places. Pollution control and improved municipal, industrial, and agricultural practices could do much to curb the cultural eutrophication of inland and coastal waters.

What is the effect of water blooms on the surface?

Water blooms, or great concentrations of algae and microscopic organisms, often develop on the surface, preventing the light penetration and oxygen absorption necessary for underwater life. Eutrophic waters are often murky and may support fewer large animals, such as fish and birds, than non-eutrophic waters. …

What is the threshold for a stratified system?

This is particularly true of stratified systems such as, for instance, lakes during summer when concentrations of molecular oxygen may reach levels of less than about one milligram per litre —a threshold for various biological and chemical processes.

What is an encyclopedia editor?

Encyclopaedia Britannica’s editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree.

What is the term for an increase in nutrients such as nitrogen and phosphorus that increase algal growth?

Eutrophication. Eutrophication has been the focus of scientific studies for more than 40 years. Although many definitions exist 1, it is generally defined as an increase in nutrients such as nitrogen and phosphorus that increase algal growth. Depending on the degree of eutrophication, severe environmental effects can develop, …

How does eutrophication happen?

Eventually, the process ends and the basin becomes colonized by terrestrial vegetation 3. The timing of natural eutrophication is highly variable and depends on the characteristics of the basin, watershed, and climate 1. However, humans, by altering nutrient inputs, have greatly increased the pace at which eutrophication can occur.

How does eutrophication affect water clarity?

Eutrophication reduces the clarity of water and underwater light. In eutrophic lakes, algae are starved for light. When algae don’t have enough light they stop producing oxygen and in turn begin consuming oxygen. Moreover, when the large blooms of algae begin to die, bacterial decomposers further deplete the levels of oxygen.

Why are there laws and regulations that support high water quality standards?

Laws and regulations have been established that support high water quality standards. Often they specifically limit nitrogen and phosphorus inputs, simply because the effects of eutrophication, though reversible, can be quite devastating.

What was used to create a barrier between two sides of Lake 226?

The experiment at Lake 226, arguably one of the most important, used a large curtain to create a barrier between two sides of the lake. Nutrient additions of carbon and nitrogen were added to both sides, but one side was also fertilized with phosphorus.

What happens when algae blooms die?

Moreover, when the large blooms of algae begin to die, bacterial decomposers further deplete the levels of oxygen. As a result, eutrophication can quickly remove much of the oxygen from a lake, leading to an anoxic — and lethal — underwater environment.

Is eutrophication human or natural?

The process of eutrophication can be both natural and human-induced. Natural eutrophication, where the basin gradually fills in from nutrient and sediment inputs, occurs over long time periods – on the order of centuries.

How does fish farming affect water quality?

The Pollution of Waterways and the Water Supply. As discussed early, fish farming uses a lot of chemicals in the production process. The combination of fertilizers, chemicals added fishmeal and water, antibiotics, and pesticides can make the water runoff from fish farms toxic. This water will find its way into local waterways …

What is fish farming?

Fish farming is the industrial practice of aquaculture where huge quantities of fish are bred and raised in enclosed, unnatural conditions and to be slaughtered in a commercial setting and sold as food. Approximately half of all fish eaten around the world come from industrial fish farms. Farmed fish are typically grown in large tanks, …

What are the toxic chemicals in fish?

Other alarming chemicals that are typically found in farmed fish include dibutyltin, Polybrominated Diphenyl Ether (PBDE), and dioxins. Dibutyltin, which is commonly used in the production of PVC plastic, can increase the risk of prediabetes and obesity if consumed by humans.

How much of the world’s food will come from fish farming?

A study produced by the World Bank, Food and Agriculture Organization of the United Nations (FAO), and the International Food Policy Research Institute (IFPRI) predicted that by the year 2030, two-thirds of the global food fish supply will come from fish farming. While many people within the fish industry say that fish farming is done …

Why was PCB banned?

PCBs cause cancer in animals are probably human carcinogens, and their production was banned by the United States government in 1978 after discovering just how toxic this chemical actually is . Many studies show that PCB is highly prevalent in the fishmeal that is fed to farmed fish.

What happens when a fish farm closes?

When a fish farm closes, regardless of the reason, they leave behind an ecological mess that can take a very long time to recover. The soil surrounding a fish farm operation will take a major hit. The soil will remain hypersaline, acidic, and eroded.

How does industrial fishing affect the ocean?

Current industrial fishing practices are trawling the ocean dry and killing countless lives to provide humans with something that is unnecessary to our survival. Industrial fish farming practices are not just killing billions of fish every single year, but also poisoning people and local ecosystems.

What are the HABs in fish?

HABs are the blooms of toxin-producing algae that kill fish and make shellfish poisonous. Consuming shellfish contaminated with toxins causes severe intoxications. Also, growth of cyanobacterial populations can pose a significant water-quality issue. Consumers need to be warned by a controlled system involving frequent analytical measurements, which necessitates the search for new, rapid, and effective methods to detect marine toxins ( European Centre for the Validation of Alternative Methods, 2006; Fux et al., 2007 ). Obtaining appropriate history and specimens, along with the knowledge of specific seafood toxicity symptoms, is also necessary to consider differential diagnosis and to confirm the diagnosis and institute the correct treatment. The lack of progress in epidemiology of disease caused by harmful marine phytoplankton is attributed to the lack of clinical testing methods, leading to underestimation of the incidence of such poisonings, especially because many of the symptoms are similar to viral and bacterial infections. Epidemiology studies are limited to the more descriptive clinically identified cases and little else. The lack of biomarkers is a hindrance, because it is possible to confirm poisoning only in their acute stage and as long as the sample food remains available. Ideally, biomarkers should allow for the identification in subclinical cases. Other factors important in detection are the efficiency in testing, precocity in its application, and cost ( Otero, 2014 ). Studies for establishing epidemiological associations between various factors and intoxication caused can be carried out by understanding the conditions that cause the explosive growth and the factors causing specific toxic event in humans. Knowing the environmental and feeding factors for poisoning allows us to establish risk zones of varying degrees. Understanding of seasonal events or cyclical phenomena along with these factors could contribute in preventing toxic episodes ( Otero, 2014 ).

What are harmful algal blooms?

Harmful algal blooms (HABs) periodically kill fish or disrupt food sources for fish and shellfish. When HABs are not detected, seafood taken from such waters may be harmful for human health. HABs can cover huge areas, often stimulated by the right combination of temperature, salinity, nutrient, sunlight, and tidal conditions. When they discolor the water, they are typically called ‘red tides.’ Sometimes HABs can be highly localized as in the case of coral reefs where reef damage due to storms or construction can disrupt the marine ecology. Human intoxications by planktonic biotoxins result from the consumption of contaminated seafood, such as shellfish and fish. Marine biotoxins are produced by various species of dinoflagellates under certain conditions. Shellfish, which are filter feeders, accumulate the biotoxins without adverse effects and without any apparent organoleptic changes. Different types of intoxications have been described based on their major symptoms, including paralytic shellfish poisoning, diarrheic shellfish poisoning, neurotoxic shellfish poisoning, amnesic shellfish poisoning, and azaspiracid poisoning. Recent warming of the world’s oceans has altered the distribution and range of dinoflagellates that make these toxins, introducing the problem to previously unaffected areas.

Can cyanobacteria kill fish?

A significant number of toxic cyanobacteria may be able to kill fish if exposed to growing blooms in eutrophicated water bodies. However, cyanobacteria are, as well as microalgae, important components of the diet of cichlids and cyprinidae fish. However, as reported earlier for other animals in this chapter, the relevant question for cyanotoxins effect is the source and the way it enters (or is administrated) in the fish. The pure toxin, extracts, or whole cells administrated by gavage (force feeding through mouth into the stomach) showed gastrointestinal uptake and caused hepatic necrosis followed by fish deaths. The immersion of adults and juveniles in contaminated waters simply did not cause toxic effects ( Tencalla et al., 1994 ). Similarly, tilapia and silver carp when exposed to equal concentrations of toxic and nontoxic M. aeruginosa are able to discriminate them by free toxins released by cells even at concentrations below 250 ng L − 1. A possible mechanism involved starts by the fish feeding via filtration and retention on the gills which would reject some toxic cells. However, gill damage was mostly caused by the higher pH induced by photosynthesis activity prior to the bloom collapse, along with ammonia released from the decomposition of cyanobacteria. Histopathological investigation of fish deaths normally points to damage in gills, digestive tract, and liver ( Rodger et al., 1994 ). A similar study with carps under natural field conditions in Australia fishes presented atrophy of hepatocytes, gills with pint point necrosis, epithelial ballooning, folded lamellar tips, exfoliation of the lamellar epithelium, elevated AST, and high serum bilirubin concentrations ( Carbis et al., 1997 ).


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