![River algae Sichuan](https://upload.wikimedia.org/wikipedia/commons/7/74/River_algae_Sichuan.jpg)
Eutrophication is the process by which an entire
body of water
A body of water or waterbody (often spelled water body) is any significant accumulation of water on the surface of Earth or another planet. The term most often refers to oceans, seas, and lakes, but it includes smaller pools of water such as p ...
, or parts of it, becomes progressively enriched with
mineral
In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. ( ...
s and
nutrient
A nutrient is a substance used by an organism to survive, grow, and reproduce. The requirement for dietary nutrient intake applies to animals, plants, fungi, and protists. Nutrients can be incorporated into cells for metabolic purposes or excret ...
s, particularly
nitrogen
Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...
and
phosphorus
Phosphorus is a chemical element with the symbol P and atomic number 15. Elemental phosphorus exists in two major forms, white phosphorus and red phosphorus, but because it is highly reactive, phosphorus is never found as a free element on Ear ...
. It has also been defined as "nutrient-induced increase in
phytoplankton
Phytoplankton () are the autotrophic (self-feeding) components of the plankton community and a key part of ocean and freshwater ecosystems. The name comes from the Greek words (), meaning 'plant', and (), meaning 'wanderer' or 'drifter'.
Ph ...
productivity".
Water bodies with very low nutrient levels are termed
oligotrophic and those with moderate nutrient levels are termed
mesotrophic. Advanced eutrophication may also be referred to as
dystrophic
Dystrophic lakes, also known as humic lakes, are lakes that contain high amounts of humic substances and organic acids. The presence of these substances causes the water to be brown in colour and have a generally low pH of around 4.0-6.0. Due to ...
and hypertrophic conditions. Eutrophication can affect
freshwater
Fresh water or freshwater is any naturally occurring liquid or frozen water containing low concentrations of dissolved salts and other total dissolved solids. Although the term specifically excludes seawater and brackish water, it does include ...
or
salt water
Saline water (more commonly known as salt water) is water that contains a high concentration of dissolved salts (mainly sodium chloride). On the United States Geological Survey (USGS) salinity scale, saline water is saltier than brackish water, ...
systems. In
freshwater ecosystem
Freshwater ecosystems are a subset of Earth's aquatic ecosystems. They include lakes, ponds, rivers, streams, springs, bogs, and wetlands. They can be contrasted with marine ecosystems, which have a larger salt content. Freshwater habitats ...
s it is almost always caused by excess phosphorus.
In
coastal waters
The coast, also known as the coastline or seashore, is defined as the area where land meets the ocean, or as a line that forms the boundary between the land and the coastline. The Earth has around of coastline. Coasts are important zones in n ...
on the other hand, the main contributing nutrient is more likely to be nitrogen, or nitrogen and phosphorus together. This depends on the location and other factors.
When occurring naturally, eutrophication is a very slow process in which nutrients, especially phosphorus compounds and organic matter, accumulate in water bodies. These nutrients derive from degradation and solution of minerals in rocks and by the effect of
lichen
A lichen ( , ) is a composite organism that arises from algae or cyanobacteria living among filaments of multiple fungi species in a mutualistic relationship.[moss
Mosses are small, non-vascular flowerless plants in the taxonomic division Bryophyta (, ) '' sensu stricto''. Bryophyta (''sensu lato'', Schimp. 1879) may also refer to the parent group bryophytes, which comprise liverworts, mosses, and hor ...]
es and
fungi
A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately from ...
actively scavenging nutrients from rocks.
Anthropogenic or "cultural eutrophication" is often a much more rapid process in which nutrients are added to a water body from a wide variety of polluting inputs including untreated or partially treated
sewage
Sewage (or domestic sewage, domestic wastewater, municipal wastewater) is a type of wastewater that is produced by a community of people. It is typically transported through a sewer system. Sewage consists of wastewater discharged from residenc ...
,
industrial wastewater
Industrial wastewater treatment describes the processes used for Wastewater treatment, treating wastewater that is produced by industries as an undesirable by-product. After treatment, the treated industrial wastewater (or effluent) may be reuse ...
and
fertilizer
A fertilizer (American English) or fertiliser (British English; see spelling differences) is any material of natural or synthetic origin that is applied to soil or to plant tissues to supply plant nutrients. Fertilizers may be distinct from ...
from farming practices.
Nutrient pollution
Nutrient pollution, a form of water pollution, refers to contamination by excessive inputs of nutrients. It is a primary cause of eutrophication of surface waters (lakes, rivers and coastal waters), in which excess nutrients, usually nitrogen or ...
, a form of
water pollution
Water pollution (or aquatic pollution) is the contamination of water bodies, usually as a result of human activities, so that it negatively affects its uses. Water bodies include lakes, rivers, oceans, aquifers, reservoirs and groundwater. Water ...
, is a primary cause of eutrophication of
surface water
Surface water is water located on top of land forming terrestrial (inland) waterbodies, and may also be referred to as ''blue water'', opposed to the seawater and waterbodies like the ocean.
The vast majority of surface water is produced by prec ...
s, in which excess nutrients, usually nitrogen or phosphorus, stimulate
algal
Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular mic ...
and
aquatic plant
Aquatic plants are plants that have adapted to living in aquatic environments (saltwater or freshwater). They are also referred to as hydrophytes or macrophytes to distinguish them from algae and other microphytes. A macrophyte is a plant that ...
growth.
A common visible effect of eutrophication is
algal bloom
An algal bloom or algae bloom is a rapid increase or accumulation in the population of algae in freshwater or marine water systems. It is often recognized by the discoloration in the water from the algae's pigments. The term ''algae'' encompas ...
s. Algal blooms can either be just a nuisance to those wanting to use the water body or become
harmful algal bloom
A harmful algal bloom (HAB) (or excessive algae growth) is an algal bloom that causes negative impacts to other organisms by production of natural phycotoxin, algae-produced toxins, mechanical damage to other organisms, or by other means. HABs are ...
s that can cause substantial ecological degradation in water bodies.
This process may result in
oxygen depletion
Hypoxia refers to low oxygen conditions. Normally, 20.9% of the gas in the atmosphere is oxygen. The partial pressure of oxygen in the atmosphere is 20.9% of the total barometric pressure. In water, oxygen levels are much lower, approximately 7 p ...
of the water body after the bacterial degradation of the algae.
[Schindler, David and Vallentyne, John R. (2004) ''Over fertilization of the World's Freshwaters and Estuaries'', University of Alberta Press, p. 1, ]
Approaches for prevention and reversal of eutrophication include: minimizing point source pollution from sewage, and minimizing nutrient pollution from agriculture and other
nonpoint pollution sources. Shellfish in estuaries,
seaweed farming
Seaweed farming or kelp farming is the practice of cultivating and harvesting seaweed. In its simplest form, it consists of the management of naturally found batches. In its most advanced form, it consists of fully controlling the life cycle ...
and
geo-engineering
Climate engineering (also called geoengineering) is a term used for both carbon dioxide removal (CDR) and solar radiation management (SRM), also called solar geoengineering, when applied at a planetary scale.IPCC (2022Chapter 1: Introduction and F ...
in lakes are also being used, some at the experimental stage. It is important to note that the term eutrophication is widely used by both scientists and public policy-makers, giving it a myriad of definitions.
Causes and mechanisms
Increasing biomass generation
Eutrophication is a process of increasing biomass generation in a water body caused by increasing concentrations of plant nutrients, most commonly
phosphate
In chemistry, a phosphate is an anion, salt, functional group or ester derived from a phosphoric acid. It most commonly means orthophosphate, a derivative of orthophosphoric acid .
The phosphate or orthophosphate ion is derived from phospho ...
and
nitrate
Nitrate is a polyatomic ion
A polyatomic ion, also known as a molecular ion, is a covalent bonded set of two or more atoms, or of a metal complex, that can be considered to behave as a single unit and that has a net charge that is not zer ...
.
Increasing nutrient concentrations lead to increasing growth of
aquatic plant
Aquatic plants are plants that have adapted to living in aquatic environments (saltwater or freshwater). They are also referred to as hydrophytes or macrophytes to distinguish them from algae and other microphytes. A macrophyte is a plant that ...
s, both macrophytes and
phytoplankton
Phytoplankton () are the autotrophic (self-feeding) components of the plankton community and a key part of ocean and freshwater ecosystems. The name comes from the Greek words (), meaning 'plant', and (), meaning 'wanderer' or 'drifter'.
Ph ...
.
As more plant material becomes available as a food resource, there are associated increases in
invertebrate
Invertebrates are a paraphyletic group of animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This is a grouping including all animals apart from the chordate ...
s and
fish
Fish are aquatic, craniate, gill-bearing animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish as well as various extinct related groups. Approximately 95% of li ...
species. As the process continues, the biomass of the water body increases and biological diversity decreases.
With more severe eutrophication, bacterial degradation of the excess biomass results in oxygen consumption, which can create a state of
hypoxia, beginning in the bottom sediment and deeper waters. Hypoxic zones are commonly found in deep water lakes in the summer season due to stratification into the cold oxygen-poor
hypolimnion
The hypolimnion or under lake is the dense, bottom layer of water in a thermally- stratified lake. The word hypolimnion is derived from the Greek "limnos" meaning "lake". It is the layer that lies below the thermocline.
Typically the hypolimni ...
and the warm oxygen-rich
epilimnion
The epilimnion or surface layer is the top-most layer in a thermally stratified lake. It sits above the deeper metalimnion and hypolimnion. It is typically warmer and has a higher pH and higher dissolved oxygen concentration than the hypolimnion ...
.
Strongly eutrophic freshwaters can become hypoxic throughout their depth following
severe algal blooms or macrophyte overgrowths. Similarly in marine systems, both increasing nutrient concentrations and isolation of bodies of water from contact with the atmosphere, can lead to depletion of oxygen which can make these waters inhospitable to fish and invertebrates.
Phosphorus is a necessary nutrient for plants to live, and is the limiting factor for plant growth in most freshwater ecosystems.
Phosphate adheres tightly to soil particles, so it is mainly transported by erosion and runoff. Once translocated to lakes, the extraction of phosphate into water is slow, hence the difficulty of reversing the effects of eutrophication.
[Khan, M. Nasir and Mohammad, F. (2014 ) "Eutrophication of Lakes" in A. A. Ansari, S. S. Gill (eds.), ''Eutrophication: Challenges and Solutions''; Volume II of ''Eutrophication: Causes, Consequences and Control'', Springer Science+Business Media Dordrecht. . .]
In
marine ecosystem
Marine ecosystems are the largest of Earth's aquatic ecosystems and exist in waters that have a high salt content. These systems contrast with freshwater ecosystems, which have a lower salt content. Marine waters cover more than 70% of the surf ...
s nitrogen and iron are the primary limiting nutrients for the accumulation of algal biomass, but more generally in marine systems nitrogen, phosphorus and iron can all be limiting.
The limitation of productivity in any particular aquatic system at any one time varies with the rate of supply of nutrients from external sources as well as nutrient recycling within the water body. Nutrient limitation of productivity also depends on the rate at which nutrients and algae are physically flushed out of that system or region. In addition light is an essential factor so productivity will be low at depth and in temperate winter when light levels are low.
Sources of nutrients
The sources of excess phosphate are
phosphates in detergent Phosphates in detergent refers to the use of phosphates as an ingredient in a detergent product. The advantage of using phosphates in a consumer laundry detergent or dishwashing detergent is that they make detergents more efficient by chelating ca ...
, industrial/domestic run-offs, and fertilizers. With the phasing out of phosphate-containing detergents in the 1970s, industrial/domestic run-off, sewage and agriculture have emerged as the dominant contributors to eutrophication.
[Werner, Wilfried (2002) "Fertilizers, 6. Environmental Aspects". ''Ullmann's Encyclopedia of Industrial Biology'', Wiley-VCH, Weinheim. ] The main sources of nitrogen beside natural
nitrogen fixation
Nitrogen fixation is a chemical process by which molecular nitrogen (), with a strong triple covalent bond, in the air is converted into ammonia () or related nitrogenous compounds, typically in soil or aquatic systems but also in industry. Atmo ...
are from agricultural runoff (from fertilizers and animal wastes), from sewage and from atmospheric deposition of nitrogen originating from combustion or animal waste.
Sources of anthropogenic nutrient pollution
Types
Cultural eutrophication
![Algae_bloom_in_Reflecting_Pool,_Washington,_DC](https://upload.wikimedia.org/wikipedia/commons/5/59/Algae_bloom_in_Reflecting_Pool%2C_Washington%2C_DC._2007_Potomac_River%2C_Chesapeake_Bay_watershed._USEPA_photo_by_Eric_Vance_%2813765962984%29.jpg)
Cultural or
anthropogenic eutrophication is the process that speeds up natural eutrophication because of human activity.
[Cultural eutrophication](_blank)
(2010) ''Encyclopedia Britannica''. Retrieved April 26, 2010, from Encyclopedia Britannica Online: Due to clearing of land and building of towns and cities,
land runoff
Surface runoff (also known as overland flow) is the flow of water occurring on the ground surface when excess rainwater, stormwater, meltwater, or other sources, can no longer sufficiently rapidly infiltrate in the soil. This can occur when the ...
is accelerated and more nutrients such as
phosphate
In chemistry, a phosphate is an anion, salt, functional group or ester derived from a phosphoric acid. It most commonly means orthophosphate, a derivative of orthophosphoric acid .
The phosphate or orthophosphate ion is derived from phospho ...
s and
nitrate
Nitrate is a polyatomic ion
A polyatomic ion, also known as a molecular ion, is a covalent bonded set of two or more atoms, or of a metal complex, that can be considered to behave as a single unit and that has a net charge that is not zer ...
are supplied to lakes and rivers, and then to coastal
estuaries
An estuary is a partially enclosed coastal body of brackish water with one or more rivers or streams flowing into it, and with a free connection to the open sea. Estuaries form a transition zone between river environments and maritime environmen ...
and bays. Cultural eutrophication results when excessive nutrients from human activities end up in water bodies creating
nutrient pollution
Nutrient pollution, a form of water pollution, refers to contamination by excessive inputs of nutrients. It is a primary cause of eutrophication of surface waters (lakes, rivers and coastal waters), in which excess nutrients, usually nitrogen or ...
and also accelerating the natural process of eutrophication.
The problem became more apparent following the introduction of chemical fertilizers in agriculture (green revolution of the mid-1900s). Phosphorus and nitrogen are the two main nutrients that cause cultural eutrophication as they enrich the water, allowing for some aquatic plants, especially algae to grow rapidly and bloom in high densities. Algal blooms can shade out benthic plants thereby altering the overall plant community.
When
algae
Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular mic ...
die off, their degradation by bacteria removes oxygen, potentially, generating
anoxic
The term anoxia means a total depletion in the level of oxygen, an extreme form of hypoxia or "low oxygen". The terms anoxia and hypoxia are used in various contexts:
* Anoxic waters, sea water, fresh water or groundwater that are depleted of diss ...
conditions. This anoxic environment kills off aerobic organisms (e.g. fish and invertebrates) in the water body. This also affects terrestrial animals, restricting their access to affected water (e.g. as drinking sources). Selection for algal and aquatic plant species that can thrive in nutrient-rich conditions can cause structural and functional disruption to entire aquatic ecosystems and their food webs, resulting in loss of habitat and species biodiversity.
There are several sources of excessive nutrients from human activity including run-off from fertilized fields, lawns and golf courses, untreated sewage and wastewater and internal combustion of fuels creating nitrogen pollution.
[Schindler, David W., Vallentyne, John R. (2008). ''The Algal Bowl: Overfertilization of the World's Freshwaters and Estuaries'', University of Alberta Press, .] Cultural eutrophication can occur in fresh water and salt water bodies, shallow waters being the most susceptible. In shore lines and shallow lakes, sediments are frequently resuspended by wind and waves which can result in nutrient release from sediments into the overlying water, enhancing eutrophication. The deterioration of water quality caused by cultural eutrophication can therefore negatively impact human uses including potable supply for consumption, industrial uses and recreation.
Natural eutrophication
Although eutrophication is commonly caused by human activities, it can also be a natural process, particularly in lakes.
Paleolimnologists now recognise that climate change, geology, and other external influences are also critical in regulating the natural productivity of lakes. A few lakes also demonstrate the reverse process (
meiotrophication), becoming less nutrient rich with time as nutrient poor inputs slowly elute the nutrient richer water mass of the lake.
[Walker, I. R. (2006) "Chironomid overview", pp. 360–366 in S.A. EIias (ed.) ''Encyclopedia of Quaternary Science'', Vol. 1, Elsevier,] This process may be seen in artificial lakes and reservoirs which tend to be highly eutrophic on first filling but may become more oligotrophic with time. The main difference between natural and anthropogenic eutrophication is that the natural process is very slow, occurring on geological time scales.
[Callisto, Marcos; Molozzi, Joseline and Barbosa, José Lucena Etham (2014) "Eutrophication of Lakes" in A. A. Ansari, S. S. Gill (eds.), ''Eutrophication: Causes, Consequences and Control'', Springer Science+Business Media Dordrecht. . .]
Effects
Ecological effects
Eutrophication can have the following ecological effects: increased biomass of
phytoplankton
Phytoplankton () are the autotrophic (self-feeding) components of the plankton community and a key part of ocean and freshwater ecosystems. The name comes from the Greek words (), meaning 'plant', and (), meaning 'wanderer' or 'drifter'.
Ph ...
, changes in
macrophyte species composition and
biomass
Biomass is plant-based material used as a fuel for heat or electricity production. It can be in the form of wood, wood residues, energy crops, agricultural residues, and waste from industry, farms, and households. Some people use the terms bi ...
,
dissolved oxygen
Oxygen saturation (symbol SO2) is a relative measure of the concentration of oxygen that is dissolved or carried in a given medium as a proportion of the maximal concentration that can be dissolved in that medium at the given temperature. It ca ...
depletion, increased incidences of
fish kill
The term fish kill, known also as fish die-off, refers to a localized die-off of fish populations which may also be associated with more generalized mortality of aquatic life.University of Florida. Gainesville, FL (2005) ''Plant Management in Fl ...
s, loss of desirable fish species.
Decreased biodiversity
When an ecosystem experiences an increase in nutrients,
primary producer
Primary or primaries may refer to:
Arts, entertainment, and media Music Groups and labels
* Primary (band), from Australia
* Primary (musician), hip hop musician and record producer from South Korea
* Primary Music, Israeli record label
Works
* ...
s reap the benefits first. In aquatic ecosystems, species such as
algae
Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular mic ...
experience a population increase (called an
algal bloom
An algal bloom or algae bloom is a rapid increase or accumulation in the population of algae in freshwater or marine water systems. It is often recognized by the discoloration in the water from the algae's pigments. The term ''algae'' encompas ...
). Algal blooms limit the sunlight available to bottom-dwelling organisms and cause wide swings in the amount of dissolved oxygen in the water. Oxygen is required by all aerobically
respiring plants and animals and it is replenished in daylight by
photosynthesizing
Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. Some of this chemical energy is stored in ...
plants and algae. Under eutrophic conditions, dissolved oxygen greatly increases during the day, but is greatly reduced after dark by the respiring algae and by microorganisms that feed on the increasing mass of dead algae. When dissolved oxygen levels decline to
hypoxic
Hypoxia means a lower than normal level of oxygen, and may refer to:
Reduced or insufficient oxygen
* Hypoxia (environmental), abnormally low oxygen content of the specific environment
* Hypoxia (medical), abnormally low level of oxygen in the t ...
levels, fish and other
marine animals
Marine life, sea life, or ocean life is the plants, animals and other organisms that live in the salt water of seas or oceans, or the brackish water of coastal estuaries. At a fundamental level, marine life affects the nature of the planet. M ...
suffocate. As a result, creatures such as fish, shrimp, and especially immobile bottom dwellers die off.
In extreme cases,
anaerobic
Anaerobic means "living, active, occurring, or existing in the absence of free oxygen", as opposed to aerobic which means "living, active, or occurring only in the presence of oxygen." Anaerobic may also refer to:
* Anaerobic adhesive, a bonding a ...
conditions ensue, promoting growth of bacteria. Zones where this occurs are known as
dead zones.
New species invasion
Eutrophication may cause competitive release by making abundant a normally
limiting nutrient
A limiting factor is a variable of a system that causes a noticeable change in output or another measure of a type of system. The limiting factor is in a pyramid shape of organisms going up from the producers to consumers and so on. A factor not l ...
. This process causes shifts in the species composition of ecosystems. For instance, an increase in nitrogen might allow new,
competitive species to invade and out-compete original inhabitant species. This has been shown to occur in
New England
New England is a region comprising six states in the Northeastern United States: Connecticut, Maine, Massachusetts, New Hampshire, Rhode Island, and Vermont. It is bordered by the state of New York to the west and by the Canadian provinces ...
salt marsh
A salt marsh or saltmarsh, also known as a coastal salt marsh or a tidal marsh, is a coastal ecosystem in the upper coastal intertidal zone between land and open saltwater or brackish water that is regularly flooded by the tides. It is dominated ...
es.
In Europe and Asia, the
common carp frequently lives in naturally eutrophic or hypereutrophic areas, and is adapted to living in such conditions. The eutrophication of areas outside its natural range partially explain the fish's success in colonizing these areas after being introduced.
Toxicity
Some
harmful algal bloom
A harmful algal bloom (HAB) (or excessive algae growth) is an algal bloom that causes negative impacts to other organisms by production of natural phycotoxin, algae-produced toxins, mechanical damage to other organisms, or by other means. HABs are ...
s resulting from eutrophication, are
toxic
Toxicity is the degree to which a chemical substance or a particular mixture of substances can damage an organism. Toxicity can refer to the effect on a whole organism, such as an animal, bacterium, or plant, as well as the effect on a subst ...
to plants and animals. Toxic compounds can make their way up the
food chain
A food chain is a linear network of links in a food web starting from producer organisms (such as grass or algae which produce their own food via photosynthesis) and ending at an apex predator species (like grizzly bears or killer whales), det ...
, resulting in animal mortality.
Freshwater algal blooms can pose a threat to livestock. When the algae die or are eaten,
neuro- and
hepatotoxins
Hepatotoxicity (from ''hepatic toxicity'') implies chemical-driven liver damage. Drug-induced liver injury is a cause of acute and chronic liver disease caused specifically by medications and the most common reason for a drug to be withdrawn fro ...
are released which can kill animals and may pose a threat to humans.
An example of algal toxins working their way into humans is the case of
shellfish
Shellfish is a colloquial and fisheries term for exoskeleton-bearing aquatic invertebrates used as food, including various species of molluscs, crustaceans, and echinoderms. Although most kinds of shellfish are harvested from saltwater envir ...
poisoning.
Biotoxins created during algal blooms are taken up by shellfish (
mussels
Mussel () is the common name used for members of several families of bivalve molluscs, from saltwater and freshwater habitats. These groups have in common a shell whose outline is elongated and asymmetrical compared with other edible clams, which ...
,
oysters), leading to these human foods acquiring the toxicity and poisoning humans. Examples include
paralytic
Paralysis (also known as plegia) is a loss of motor function in one or more muscles. Paralysis can also be accompanied by a loss of feeling (sensory loss) in the affected area if there is sensory damage. In the United States, roughly 1 in 50 ...
, neurotoxic, and
diarrhoetic shellfish poisoning. Other marine animals can be
vectors for such toxins, as in the case of
ciguatera
Ciguatera fish poisoning (CFP), also known simply as ciguatera, is a foodborne illness caused by eating reef fish whose flesh is contaminated with certain toxins. Such individual fish are said to be ciguatoxic. Symptoms may include diarrhea, vomi ...
, where it is typically a predator fish that accumulates the toxin and then poisons humans.
Economic effects
Eutrophication and harmful algal blooms can have economic impacts due to increasing
water treatment
Water treatment is any process that improves the quality of water to make it appropriate for a specific end-use. The end use may be drinking, industrial water supply, irrigation, river flow maintenance, water recreation or many other uses, inc ...
costs, commercial fishing and shellfish losses, recreational fishing losses (reductions in harvestable fish and
shellfish
Shellfish is a colloquial and fisheries term for exoskeleton-bearing aquatic invertebrates used as food, including various species of molluscs, crustaceans, and echinoderms. Although most kinds of shellfish are harvested from saltwater envir ...
), and reduced tourism income (decreases in perceived aesthetic value of the water body). Water treatment costs can be increased due to decreases in water transparency (increased
turbidity
Turbidity is the cloudiness or haziness of a fluid caused by large numbers of individual particles that are generally invisible to the naked eye, similar to smoke in air. The measurement of turbidity is a key test of water quality.
Fluids can ...
). There can also be issues with color and smell during drinking water treatment.
Health impacts
Human health effects include excess nitrate in drinking water (
blue baby syndrome
Blue baby syndrome can refer to conditions that cause cyanosis, or blueness of the skin, in babies as a result of low oxygen levels in the blood. This term has traditionally been applied to cyanosis as a result of:
#Cyanotic heart disease, whi ...
);
disinfection by-product
Disinfection by-products (DBPs) result from chemical reactions between organic and inorganic matter in water with chemical treatment agents during the water disinfection process.
Chlorination disinfection byproducts
Chlorinated disinfection agen ...
s in drinking water. Swimming in water affected by a harmful algal bloom can cause cause skin rashes and respiratory problems.
Causes and effects for different types of water bodies
Freshwater systems
One response to added amounts of nutrients in
aquatic ecosystem
An aquatic ecosystem is an ecosystem formed by surrounding a body of water, in contrast to land-based terrestrial ecosystems. Aquatic ecosystems contain communities of organisms that are dependent on each other and on their environment. The tw ...
s is the rapid growth of microscopic algae, creating an
algal bloom
An algal bloom or algae bloom is a rapid increase or accumulation in the population of algae in freshwater or marine water systems. It is often recognized by the discoloration in the water from the algae's pigments. The term ''algae'' encompas ...
. In
freshwater ecosystem
Freshwater ecosystems are a subset of Earth's aquatic ecosystems. They include lakes, ponds, rivers, streams, springs, bogs, and wetlands. They can be contrasted with marine ecosystems, which have a larger salt content. Freshwater habitats ...
s, the formation of floating algal blooms are commonly nitrogen-fixing
cyanobacteria
Cyanobacteria (), also known as Cyanophyta, are a phylum of gram-negative bacteria that obtain energy via photosynthesis. The name ''cyanobacteria'' refers to their color (), which similarly forms the basis of cyanobacteria's common name, blu ...
(blue-green algae). This outcome is favored when soluble nitrogen becomes limiting and phosphorus inputs remain significant.
Nutrient pollution
Nutrient pollution, a form of water pollution, refers to contamination by excessive inputs of nutrients. It is a primary cause of eutrophication of surface waters (lakes, rivers and coastal waters), in which excess nutrients, usually nitrogen or ...
is a major cause of algal blooms and excess growth of other aquatic plants leading to overcrowding competition for sunlight, space, and oxygen. Increased competition for the added nutrients can cause potential disruption to entire ecosystems and food webs, as well as a loss of habitat, and biodiversity of species.
When
macrophytes and algae die in over-productive eutrophic lakes, rivers and streams, they decompose and the nutrients contained in that organic matter are converted into inorganic form by microorganisms. This decomposition process consumes oxygen, which reduces the concentration of dissolved oxygen. The depleted oxygen levels in turn may lead to
fish kill
The term fish kill, known also as fish die-off, refers to a localized die-off of fish populations which may also be associated with more generalized mortality of aquatic life.University of Florida. Gainesville, FL (2005) ''Plant Management in Fl ...
s and a range of other effects reducing biodiversity. Nutrients may become concentrated in an anoxic zone, often in deeper waters cut off by stratification of the water column and may only be made available again during autumn turn-over in temperate areas or in conditions of turbulent flow. The dead algae and organic load carried by the water inflows into a lake settle to the bottom and undergo
anaerobic digestion
Anaerobic digestion is a sequence of processes by which microorganisms break down biodegradable material in the absence of oxygen. The process is used for industrial or domestic purposes to Waste management, manage waste or to produce fuels. Mu ...
releasing
greenhouse gases
A greenhouse gas (GHG or GhG) is a gas that absorbs and emits radiant energy within the thermal infrared range, causing the greenhouse effect. The primary greenhouse gases in Earth's atmosphere are water vapor (), carbon dioxide (), methane ...
such as methane and CO
2. Some of the methane gas may be oxidised by anaerobic
methane oxidation bacteria such as ''
Methylococcus capsulatus
''Methylococcus capsulatus'' is an obligately methanotrophic gram-negative, non-motile coccoid bacterium. ''M. capsulatus'' are thermotolerant; their cells are encapsulated and tend to have a diplococcoid shape. In addition to methane, ''M. ...
'', which in turn may provide a food source for
zooplankton
Zooplankton are the animal component of the planktonic community ("zoo" comes from the Greek word for ''animal''). Plankton are aquatic organisms that are unable to swim effectively against currents, and consequently drift or are carried along by ...
. Thus a self-sustaining biological process can take place to generate
primary food source for the
phytoplankton
Phytoplankton () are the autotrophic (self-feeding) components of the plankton community and a key part of ocean and freshwater ecosystems. The name comes from the Greek words (), meaning 'plant', and (), meaning 'wanderer' or 'drifter'.
Ph ...
and zooplankton depending on the availability of adequate dissolved oxygen in the water body.
Enhanced growth of aquatic vegetation, phytoplankton and algal blooms disrupts normal functioning of the ecosystem, causing a variety of problems such as a lack of
oxygen
Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as wel ...
which is needed for fish and
shellfish
Shellfish is a colloquial and fisheries term for exoskeleton-bearing aquatic invertebrates used as food, including various species of molluscs, crustaceans, and echinoderms. Although most kinds of shellfish are harvested from saltwater envir ...
to survive. The growth of dense algae in surface waters can shade the deeper water and reduce the viability of benthic shelter plants with resultant impacts on the wider ecosystem.
Eutrophication also decreases the value of rivers, lakes and aesthetic enjoyment. Health problems can occur where
eutrophic
Eutrophication is the process by which an entire body of water, or parts of it, becomes progressively enriched with minerals and nutrients, particularly nitrogen and phosphorus. It has also been defined as "nutrient-induced increase in phytoplan ...
conditions interfere with drinking
water treatment
Water treatment is any process that improves the quality of water to make it appropriate for a specific end-use. The end use may be drinking, industrial water supply, irrigation, river flow maintenance, water recreation or many other uses, inc ...
.
[Bartram, J., Wayne W. Carmichael, Ingrid Chorus, Gary Jones, and Olav M. Skulberg (1999). "Chapter 1. Introduction", in: ''Toxic Cyanobacteria in Water: A guide to their public health consequences, monitoring and management''. ]World Health Organization
The World Health Organization (WHO) is a specialized agency of the United Nations responsible for international public health. The WHO Constitution states its main objective as "the attainment by all peoples of the highest possible level of h ...
. URL
WHO document
Phosphorus
Phosphorus is a chemical element with the symbol P and atomic number 15. Elemental phosphorus exists in two major forms, white phosphorus and red phosphorus, but because it is highly reactive, phosphorus is never found as a free element on Ear ...
is often regarded as the main culprit in cases of eutrophication in lakes subjected to "point source" pollution from sewage pipes. The concentration of algae and the
trophic state of lakes correspond well to phosphorus levels in water. Studies conducted in the Experimental Lakes Area in Ontario have shown a relationship between the addition of phosphorus and the rate of eutrophication. Later stages of eutrophication lead to blooms of nitrogen-fixing cyanobacteria limited solely by the phosphorus concentration.
Coastal waters
Eutrophication is a common phenomenon in
coastal waters
The coast, also known as the coastline or seashore, is defined as the area where land meets the ocean, or as a line that forms the boundary between the land and the coastline. The Earth has around of coastline. Coasts are important zones in n ...
. In coastal waters, nitrogen is commonly the key limiting nutrient of
marine waters (unlike the freshwater systems where phosphorus is often the limiting nutrient). Therefore,
nitrogen
Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...
levels are more important than phosphorus levels for understanding and controlling eutrophication problems in salt water.
Estuaries
An estuary is a partially enclosed coastal body of brackish water with one or more rivers or streams flowing into it, and with a free connection to the open sea. Estuaries form a transition zone between river environments and maritime environmen ...
, as the interface between freshwater and saltwater, can be both phosphorus and nitrogen limited and commonly exhibit symptoms of eutrophication. Eutrophication in estuaries often results in bottom water hypoxia or anoxia, leading to fish kills and habitat degradation.
Upwelling in coastal systems also promotes increased productivity by conveying deep, nutrient-rich waters to the surface, where the nutrients can be assimilated by
algae
Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular mic ...
.
Examples of anthropogenic sources of nitrogen-rich pollution to coastal waters include sea cage
fish farming
upright=1.3, Salmon farming in the sea (mariculture) at Loch Ainort, Isle of Skye">mariculture.html" ;"title="Salmon farming in the sea (mariculture">Salmon farming in the sea (mariculture) at Loch Ainort, Isle of Skye, Scotland
Fish farming or ...
and discharges of
ammonia
Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous was ...
from the production of
coke from coal. In addition to runoff from land, wastes from fish farming and industrial ammonia discharges, atmospheric
fixed nitrogen can be an important nutrient source in the open ocean. This could account for around one third of the ocean's external (non-recycled) nitrogen supply, and up to 3% of the annual new marine biological production.
Coastal waters embrace a wide range of
marine habitats
Marine habitats are habitats that support marine life. Marine life depends in some way on the saltwater that is in the sea (the term ''marine'' comes from the Latin ''mare'', meaning sea or ocean). A habitat is an ecological or environmental ...
from enclosed
estuaries
An estuary is a partially enclosed coastal body of brackish water with one or more rivers or streams flowing into it, and with a free connection to the open sea. Estuaries form a transition zone between river environments and maritime environmen ...
to the
open waters of the continental shelf. Phytoplankton productivity in coastal waters depends on both nutrient and light supply, with the latter an important limiting factor in waters near to shore where sediment resuspension often limits light penetration.
Nutrients are supplied to coastal waters from land via river and groundwater and also via the atmosphere. There is also an important source from the open ocean, via mixing of relatively nutrient rich deep ocean waters.
Nutrient inputs from the ocean are little changed by human activity, although
climate change
In common usage, climate change describes global warming—the ongoing increase in global average temperature—and its effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes to E ...
may alter the water flows across the shelf break. By contrast, inputs from land to coastal zones of the nutrients nitrogen and phosphorus have been increased by human activity globally. The extent of increases varies greatly from place to place depending on human activities in the catchments. A third key nutrient, dissolved
silicon
Silicon is a chemical element with the symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic luster, and is a tetravalent metalloid and semiconductor. It is a member of group 14 in the periodic tab ...
, is derived primarily from sediment
weathering
Weathering is the deterioration of rocks, soils and minerals as well as wood and artificial materials through contact with water, atmospheric gases, and biological organisms. Weathering occurs ''in situ'' (on site, with little or no movement), ...
to rivers and from offshore and is therefore much less affected by human activity.
Effects of coastal eutrophication
These increasing nitrogen and phosphorus nutrient inputs exert eutrophication pressures on coastal zones. These pressures vary geographically depending on the catchment activities and associated nutrient load. The geographical setting of the coastal zone is another important factor as it controls dilution of the nutrient load and oxygen exchange with the atmosphere. The effects of these eutrophication pressures can be seen in several different ways:
# There is evidence from
satellite monitoring that the amounts of
chlorophyll as a measure of overall
phytoplankton
Phytoplankton () are the autotrophic (self-feeding) components of the plankton community and a key part of ocean and freshwater ecosystems. The name comes from the Greek words (), meaning 'plant', and (), meaning 'wanderer' or 'drifter'.
Ph ...
activity are increasing in many coastal areas worldwide due to increased nutrient inputs.
# The phytoplankton species composition may change due to increased nutrient loadings and changes in the proportions of key nutrients. In particular the increases in nitrogen and phosphorus inputs, along with much smaller changes in silicon inputs, create changes in the ratio of nitrogen and phosphorus to silicon. These changing nutrient ratios drive changes in phytoplankton species composition, particularly disadvantaging silica rich phytoplankton species like diatoms compared to other species.
This process leads to the development of nuisance algal blooms in areas such as the North Sea (see also
OSPAR Convention
The Convention for the Protection of the Marine Environment of the North-East Atlantic or OSPAR Convention is the current legislative instrument regulating international cooperation on environmental protection in the North-East Atlantic. Work ...
) and the
Black Sea
The Black Sea is a marginal mediterranean sea of the Atlantic Ocean lying between Europe and Asia, east of the Balkans, south of the East European Plain, west of the Caucasus, and north of Anatolia. It is bounded by Bulgaria, Georgia, Roma ...
.
In some cases nutrient enrichment can lead to
harmful algal bloom
A harmful algal bloom (HAB) (or excessive algae growth) is an algal bloom that causes negative impacts to other organisms by production of natural phycotoxin, algae-produced toxins, mechanical damage to other organisms, or by other means. HABs are ...
s (HABs). Such blooms can occur naturally, but there is good evidence that these are increasing as a result of nutrient enrichment, although the causal linkage between nutrient enrichment and HABs is not straightforward.
#
Oxygen depletion
Hypoxia refers to low oxygen conditions. Normally, 20.9% of the gas in the atmosphere is oxygen. The partial pressure of oxygen in the atmosphere is 20.9% of the total barometric pressure. In water, oxygen levels are much lower, approximately 7 p ...
has existed in some coastal seas such as the
Baltic for thousands of years. In such areas the density structure of the water column severely restricts water column mixing and associated oxygenation of deep water. However, increases in the inputs of bacterially degradable organic matter to such isolated deep waters can exacerbate such
oxygen depletion in oceans. These areas of lower dissolved oxygen have increased globally in recent decades. They are usually connected with nutrient enrichment and resulting algal blooms.
Climate change will generally tend to increase water column stratification and so exacerbate this oxygen depletion problem. An example of such coastal oxygen depletion is in the
Gulf of Mexico
The Gulf of Mexico ( es, Golfo de México) is an oceanic basin, ocean basin and a marginal sea of the Atlantic Ocean, largely surrounded by the North American continent. It is bounded on the northeast, north and northwest by the Gulf Coast of ...
where an area of seasonal anoxia more than 5000 square miles in area has developed since the 1950s. The increased primary production driving this anoxia is fueled by nutrients supplied by the
Mississippi river
The Mississippi River is the second-longest river and chief river of the second-largest drainage system in North America, second only to the Hudson Bay drainage system. From its traditional source of Lake Itasca in northern Minnesota, it f ...
. A similar process has been documented in the Black Sea.
Extent of the problem
![Orange like Autumn](https://upload.wikimedia.org/wikipedia/commons/7/71/Orange_like_Autumn.jpg)
Surveys showed that 54% of lakes in
Asia
Asia (, ) is one of the world's most notable geographical regions, which is either considered a continent in its own right or a subcontinent of Eurasia, which shares the continental landmass of Afro-Eurasia with Africa. Asia covers an area ...
are eutrophic; in
Europe
Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a Continent#Subcontinents, subcontinent of Eurasia ...
, 53%; in
North America
North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and the Car ...
, 48%; in
South America
South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the southe ...
, 41%; and in
Africa
Africa is the world's second-largest and second-most populous continent, after Asia in both cases. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 6% of Earth's total surface area ...
, 28%.
[ILEC/Lake Biwa Research Institute ds 1988–1993 Survey of the State of the World's Lakes. Volumes I-IV. International Lake Environment Committee, Otsu and United Nations Environment Programme, Nairobi.] In South Africa, a study by the CSIR using remote sensing has shown more than 60% of the reservoirs surveyed were eutrophic.
The
World Resources Institute
The World Resources Institute (WRI) is a global research non-profit organization established in 1982 with funding from the MacArthur Foundation under the leadership of James Gustave Speth. WRI's activities are focused on seven areas: food, for ...
has identified 375
hypoxic
Hypoxia means a lower than normal level of oxygen, and may refer to:
Reduced or insufficient oxygen
* Hypoxia (environmental), abnormally low oxygen content of the specific environment
* Hypoxia (medical), abnormally low level of oxygen in the t ...
coastal zones in the world, concentrated in coastal areas in Western Europe, the Eastern and Southern coasts of the US, and
East Asia
East Asia is the eastern region of Asia, which is defined in both geographical and ethno-cultural terms. The modern states of East Asia include China, Japan, Mongolia, North Korea, South Korea, and Taiwan. China, North Korea, South Korea and ...
, particularly
Japan
Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the north ...
.
Global goals
The
United Nations
The United Nations (UN) is an intergovernmental organization whose stated purposes are to maintain international peace and international security, security, develop friendly relations among nations, achieve international cooperation, and be ...
framework for
Sustainable Development Goals
The Sustainable Development Goals (SDGs) or Global Goals are a collection of 17 interlinked objectives designed to serve as a "shared blueprint for peace and prosperity for people and the planet, now and into the future".United Nations (2017) R ...
recognizes the damaging effects of eutrophication for marine environments. It has established a timeline for creating an Index of Coastal Eutrophication and Floating Plastic Debris Density (ICEP) within
Sustainable Development Goal 14
Sustainable Development Goal 14 (Goal 14 or SDG 14) is about "Life below water" and is one of the 17 Sustainable Development Goals established by the United Nations in 2015. The official wording is to "Conserve and sustainably use the oceans, seas ...
(life below water).
SDG 14 specifically has a target to: "by 2025, prevent and significantly reduce marine pollution of all kinds, in particular from land-based activities, including marine debris and nutrient pollution".
Prevention
Minimizing point source pollution from sewage
Finnish phosphorus removal measures started in the mid-1970s and have targeted rivers and lakes polluted by industrial and municipal discharges. These efforts have had a 90% removal efficiency.
Still, some targeted point sources did not show a decrease in runoff despite reduction efforts.
There are multiple different ways to fix cultural eutrophication with raw sewage being a
point source
A point source is a single identifiable ''localised'' source of something. A point source has negligible extent, distinguishing it from other source geometries. Sources are called point sources because in mathematical modeling, these sources can ...
of pollution. For example,
sewage treatment plants
Sewage treatment (or domestic wastewater treatment, municipal wastewater treatment) is a type of wastewater treatment which aims to remove contaminants from sewage to produce an effluent that is suitable for discharge to the surrounding envir ...
can be upgraded for biological nutrient removal so that they discharge much less nitrogen and phosphorus to the receiving water body. However, even with good
secondary treatment
Secondary treatment is the removal of biodegradable organic matter (in solution or suspension) from sewage or similar kinds of wastewater. The aim is to achieve a certain degree of effluent quality in a sewage treatment plant suitable for the inte ...
, most final effluents from sewage treatment works contain substantial concentrations of nitrogen as nitrate, nitrite or ammonia. Removal of these nutrients is an expensive and often difficult process.
Laws regulating the discharge and treatment of sewage have led to dramatic nutrient reductions to surrounding ecosystems.
Because a major contributor to the nonpoint source nutrient loading of water bodies is untreated domestic sewage, it is necessary to provide treatment facilities to highly urbanized areas, particularly those in
developing countries
A developing country is a sovereign state with a lesser developed industrial base and a lower Human Development Index (HDI) relative to other countries. However, this definition is not universally agreed upon. There is also no clear agreem ...
, in which treatment of domestic waste water is a scarcity. The technology to safely and efficiently
reuse wastewater, both from domestic and industrial sources, should be a primary concern for policy regarding eutrophication.
Minimizing nutrient pollution by agriculture
There are many ways to help fix cultural eutrophication caused by agriculture. Safe farming practices is the number one way to fix the problem. Some safety precautions are:
# Nutrient Management Techniques - Anyone using fertilizers should apply fertilizer in the correct amount, at the right time of year, with the right method and placement.
# Year - Round Ground Cover - a cover crop will prevent periods of bare ground thus eliminating erosion and runoff of nutrients even after the growing season has occurred.
# Planting Field Buffers - By planting trees, shrubs and grasses along the edges of fields to help catch the runoff and absorb some nutrients before the water makes it to a nearby water body.
# Conservation Tillage - By reducing frequency and intensity of tilling the land will enhance the chance of nutrients absorbing into the ground.
Minimizing nonpoint pollution
Nonpoint pollution is the most difficult source of nutrients to manage. The literature suggests, though, that when these sources are controlled, eutrophication decreases. The following steps are recommended to minimize the amount of pollution that can enter aquatic ecosystems from ambiguous sources.
Riparian buffer zones
Studies show that intercepting non-point pollution between the source and the water is a successful means of prevention.
Riparian buffer zones
A riparian zone or riparian area is the interface between land and a river or stream. Riparian is also the proper nomenclature for one of the terrestrial biomes of the Earth. Plant habitats and communities along the river margins and banks ar ...
are interfaces between a flowing body of water and land, and have been created near waterways in an attempt to filter pollutants;
sediment
Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sand an ...
and nutrients are deposited here instead of in water. Creating buffer zones near farms and roads is another possible way to prevent nutrients from traveling too far. Still, studies have shown
that the effects of atmospheric nitrogen pollution can reach far past the buffer zone. This suggests that the most effective means of prevention is from the primary source.
Prevention policy
A policy regulating agricultural use of
fertilizer
A fertilizer (American English) or fertiliser (British English; see spelling differences) is any material of natural or synthetic origin that is applied to soil or to plant tissues to supply plant nutrients. Fertilizers may be distinct from ...
and animal waste must be imposed. In Japan the amount of nitrogen produced by livestock is adequate to serve the fertilizer needs for the agriculture industry.
Thus, it is not unreasonable to command livestock owners to collect animal waste from the field, which when left stagnant will
leach
Leach may refer to:
* Leach (surname)
* Leach, Oklahoma, an unincorporated community, United States
* Leach, Tennessee, an unincorporated community, United States
* Leach Highway, Western Australia
* Leach orchid
* Leach phenotype, a mutation in ...
into ground water.
Policy concerning the prevention and reduction of eutrophication can be broken down into four sectors: Technologies, public participation, economic instruments, and cooperation.
["Planning and Management of Lakes and Reservoirs: An Integrated Approach to Eutrophication."](_blank)
United Nations Environment Programme, Newsletter and Technical Publications. International Environmental Technology Centre. Ch.3.4 (2000). The term technology is used loosely, referring to a more widespread use of existing methods rather than an appropriation of new technologies. As mentioned before, nonpoint sources of pollution are the primary contributors to eutrophication, and their effects can be easily minimized through common agricultural practices. Reducing the amount of pollutants that reach a watershed can be achieved through the protection of its forest cover, reducing the amount of erosion leeching into a watershed. Also, through the efficient, controlled use of land using sustainable agricultural practices to minimize
land degradation
Land degradation is a process in which the value of the biophysical environment is affected by a combination of human-induced processes acting upon the land.
It is viewed as any change or disturbance to the land perceived to be deleterious ...
, the amount of soil runoff and nitrogen-based fertilizers reaching a watershed can be reduced. Waste disposal technology constitutes another factor in eutrophication prevention.
The role of the public is a major factor for the effective prevention of eutrophication. In order for a policy to have any effect, the public must be aware of their contribution to the problem, and ways in which they can reduce their effects. Programs instituted to promote participation in the recycling and elimination of wastes, as well as education on the issue of rational water use are necessary to protect water quality within urbanized areas and adjacent water bodies.
Economic instruments, "which include, among others, property rights, water markets, fiscal and financial instruments, charge systems and liability systems, are gradually becoming a substantive component of the management tool set used for pollution control and water allocation decisions."
Incentives for those who practice clean, renewable, water management technologies are an effective means of encouraging pollution prevention. By internalizing the costs associated with the negative effects on the environment, governments are able to encourage a cleaner water management.
Because a body of water can have an effect on a range of people reaching far beyond that of the watershed, cooperation between different organizations is necessary to prevent the intrusion of contaminants that can lead to eutrophication. Agencies ranging from state governments to those of water resource management and non-governmental organizations, going as low as the local population, are responsible for preventing eutrophication of water bodies. In the United States, the most well known inter-state effort to prevent eutrophication is the
Chesapeake Bay
The Chesapeake Bay ( ) is the largest estuary in the United States. The Bay is located in the Mid-Atlantic (United States), Mid-Atlantic region and is primarily separated from the Atlantic Ocean by the Delmarva Peninsula (including the parts: the ...
.
Nitrogen testing and modeling
Soil nitrogen testing (N-Testing) is a technique that helps farmers optimize the amount of fertilizer applied to crops. By testing fields with this method, farmers saw a decrease in fertilizer application costs, a decrease in nitrogen lost to surrounding sources, or both.
By testing the soil and modeling the bare minimum amount of fertilizer are needed, farmers reap economic benefits while reducing pollution.
Organic farming
Organically fertilized fields can "significantly reduce harmful nitrate leaching" compared to conventionally fertilized fields.
Eutrophication impacts are in some cases higher from organic production than they are from conventional production.
Reversal and remediation
Recovering from eutrophication
![Mussels_at_Strawberry_Rocks_PC013145](https://upload.wikimedia.org/wikipedia/commons/d/d1/Mussels_at_Strawberry_Rocks_PC013145.JPG)
Reducing nutrient inputs is a key precondition for restoration, but there are two caveats: Firstly it can take a long time, particularly because of the storage of nutrients in
sediment
Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sand an ...
s. Secondly, restoration may need more than a simple reversal of inputs since there are sometimes several stable but very different ecological states. Recovery of eutrophicated lakes is slow, often requiring several decades.
Innovative solutions have been conceived to deal with nutrient pollution in aquatic systems by altering or enhancing natural processes to shift nutrient effects away from detrimental ecological impacts. Nutrient remediation is a form of environmental remediation, but concerns only biologically active nutrients such as
nitrogen
Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...
and
phosphorus
Phosphorus is a chemical element with the symbol P and atomic number 15. Elemental phosphorus exists in two major forms, white phosphorus and red phosphorus, but because it is highly reactive, phosphorus is never found as a free element on Ear ...
. "Remediation" refers to the removal of pollution or contaminants, generally for the protection of human health. In
environmental remediation nutrient removal technologies include
biofiltration
Biofiltration is a pollution control technique using a bioreactor containing living material to capture and biologically degrade pollutants. Common uses include processing waste water, capturing harmful chemicals or silt from surface runoff, an ...
, which uses living material to capture and biologically degrade pollutants. Examples include green belts,
riparian
A riparian zone or riparian area is the interface between land and a river or stream. Riparian is also the proper nomenclature for one of the terrestrial biomes of the Earth. Plant habitats and communities along the river margins and banks a ...
areas, natural and constructed wetlands, and treatment ponds. These areas most commonly capture anthropogenic discharges such as wastewater, stormwater runoff, or sewage treatment, for land reclamation after mining, refinery activity, or land development. Biofiltration utilizes
biological assimilation to capture, absorb, and eventually incorporate the pollutants (including nutrients) into living tissue. Another form of nutrient removal is
bioremediation
Bioremediation broadly refers to any process wherein a biological system (typically bacteria, microalgae, fungi, and plants), living or dead, is employed for removing environmental pollutants from air, water, soil, flue gasses, industrial effluent ...
, which uses microorganisms to remove pollutants. Bioremediation can occur on its own as natural attenuation or intrinsic bioremediation or can be encouraged by the addition of fertilizers, a strategy called biostimulation.
Nutrient bioextraction is bioremediation involving cultured plants and animals. Nutrient bioextraction or bioharvesting is the practice of farming and harvesting
shellfish
Shellfish is a colloquial and fisheries term for exoskeleton-bearing aquatic invertebrates used as food, including various species of molluscs, crustaceans, and echinoderms. Although most kinds of shellfish are harvested from saltwater envir ...
and
seaweed
Seaweed, or macroalgae, refers to thousands of species of macroscopic, multicellular, marine algae. The term includes some types of '' Rhodophyta'' (red), ''Phaeophyta'' (brown) and ''Chlorophyta'' (green) macroalgae. Seaweed species such as ...
for the purpose of removing nitrogen and other nutrients from natural water bodies. It has been suggested that nitrogen removal by oyster reefs could generate net benefits for sources facing nitrogen emission restrictions, similar to other nutrient trading scenarios. Specifically, if oysters maintain nitrogen levels in estuaries below thresholds that would lead to the imposition of emission limits, oysters effectively save the sources the compliance costs they otherwise would incur. Several studies have shown that oysters and mussels have the capacity to dramatically impact nitrogen levels in estuaries. Additionally, studies have demonstrated seaweed's potential to improve nitrogen levels.
Shellfish in estuaries
One proposed solution to stop and reverse eutrophication in estuaries is to restore shellfish populations, such as oysters and mussels. Oyster reefs remove
nitrogen
Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...
from the water column and filter out suspended solids, subsequently reducing the likelihood or extent of
harmful algal blooms or anoxic conditions. Filter feeding activity is considered beneficial to water quality by controlling phytoplankton density and sequestering nutrients, which can be removed from the system through shellfish harvest, buried in the sediments, or lost through
denitrification
Denitrification is a microbially facilitated process where nitrate (NO3−) is reduced and ultimately produces molecular nitrogen (N2) through a series of intermediate gaseous nitrogen oxide products. Facultative anaerobic bacteria perform denitr ...
. Foundational work toward the idea of improving marine water quality through shellfish cultivation was conducted by Odd Lindahl et al., using
mussels
Mussel () is the common name used for members of several families of bivalve molluscs, from saltwater and freshwater habitats. These groups have in common a shell whose outline is elongated and asymmetrical compared with other edible clams, which ...
in Sweden. In the United States, shellfish restoration projects have been conducted on the East, West and Gulf coasts. See
nutrient pollution
Nutrient pollution, a form of water pollution, refers to contamination by excessive inputs of nutrients. It is a primary cause of eutrophication of surface waters (lakes, rivers and coastal waters), in which excess nutrients, usually nitrogen or ...
for an extended explanation of
nutrient remediation using shellfish.
Seaweed farming
Seaweed aquaculture offers an opportunity to mitigate, and adapt to climate change. Seaweed, such as kelp, also absorbs phosphorus and nitrogen and is thus useful to remove excessive nutrients from polluted parts of the sea. Some cultivated seaweeds have a very high productivity and could absorb large quantities of N, P, , producing large amounts of having an excellent effect on decreasing eutrophication. It is believed that seaweed cultivation in large scale should be a good solution to the eutrophication problem in
coastal waters
The coast, also known as the coastline or seashore, is defined as the area where land meets the ocean, or as a line that forms the boundary between the land and the coastline. The Earth has around of coastline. Coasts are important zones in n ...
.
Geo-engineering in lakes (chemical phosphorus removal)
![Application of a phosphorus sorbent to a lake - The Netherlands](https://upload.wikimedia.org/wikipedia/commons/3/33/Application_of_a_phosphorus_sorbent_to_a_lake_-_The_Netherlands.jpg)
Geo-engineering is the manipulation of
biogeochemical
Biogeochemistry is the scientific discipline that involves the study of the chemical, physical, geological, and biological processes and reactions that govern the composition of the natural environment (including the biosphere, the cryosphere, th ...
processes, usually the
phosphorus cycle
The phosphorus cycle is the biogeochemical cycle that describes the movement of phosphorus through the lithosphere, hydrosphere, and biosphere. Unlike many other biogeochemical cycles, the atmosphere does not play a significant role in the moveme ...
, to achieve a desired ecological response in the
ecosystem
An ecosystem (or ecological system) consists of all the organisms and the physical environment with which they interact. These biotic and abiotic components are linked together through nutrient cycles and energy flows. Energy enters the syste ...
. Geo-engineering techniques typically uses materials able to chemically inactivate the phosphorus available for organisms (i.e. phosphate) in the water column and also block the phosphate release from the sediment (internal loading). Phosphate is one of the main contributing factors to algal growth, mainly cyanobacteria, so once phosphate is reduced the algal is not able to overgrow. Thus, geo-engineering materials is used to speed-up the recovery of eutrophic water bodies and manage algal bloom. There are several phosphate sorbents in the literature, from metal salts (e.g.
alum
An alum () is a type of chemical compound, usually a hydrated double salt, double sulfate salt (chemistry), salt of aluminium with the general chemical formula, formula , where is a valence (chemistry), monovalent cation such as potassium or a ...
,
aluminium sulfate
Aluminium sulfate is a salt with the chemical formula, formula aluminium, Al2sulfate, (SO4)3. It is soluble in water and is mainly used as a Coagulation (water treatment), coagulating agent (promoting particle collision by neutralizing charge) in ...
,) minerals, natural clays and local soils, industrial waste products, modified clays (e.g. lanthanum modified bentonite) and others. The phosphate sorbent is commonly applied in the surface of the water body and it sinks to the bottom of the lake reducing phosphate, such sorbents have been applied worldwide to manage eutrophication and algal bloom (for example under the commercial name
Phoslock).
One method of eutrophication remediation uses
chemical phosphorus removal Chemical phosphorus removal is a wastewater treatment method, where phosphorus is removed using salts of aluminum (e.g. alum or polyaluminum chloride), iron (e.g. ferric chloride), or calcium (e.g. lime). Phosphate forms precipitates with the metal ...
with aluminum sulfate, a salt commonly used in the coagulation process of drinking
water treatment
Water treatment is any process that improves the quality of water to make it appropriate for a specific end-use. The end use may be drinking, industrial water supply, irrigation, river flow maintenance, water recreation or many other uses, inc ...
. Aluminum sulfate, or "alum" as it is commonly referred, is used to reduce the phosphorus load.
In a large scale study, 114 lakes were monitored for the effectiveness of alum at phosphorus reduction. Across all lakes, alum effectively reduced the phosphorus for 11 years. While there was variety in the longevity (21 years in deep lakes and 5.7 years in shallow lakes), the results express the effectiveness of alum at controlling phosphorus within lakes.
Alum treatment is less effective in deep lakes, as well as lakes with substantial external phosphorus loading.
[Cooke, G. D., Welch, E. B., Martin, A. B., Fulmer, D. G., Hyde, J. B., & Schrieve, G. D. (1993). Effectiveness of Al, Ca, and Fe salts for control of internal phosphorus loading in shallow and deep lakes. ''Hydrobiologia'', ''253''(1), 323-335.]
History
Eutrophication was recognized as a
water pollution
Water pollution (or aquatic pollution) is the contamination of water bodies, usually as a result of human activities, so that it negatively affects its uses. Water bodies include lakes, rivers, oceans, aquifers, reservoirs and groundwater. Water ...
problem in European and North American lakes and reservoirs in the mid-20th century.
[Rodhe, W. (1969) "Crystallization of eutrophication concepts in North Europe". In: ''Eutrophication, Causes, Consequences, Correctives''. National Academy of Sciences, Washington D.C., , pp. 50–64.] Breakthrough research carried out at the
Experimental Lakes Area
IISD Experimental Lakes Area (IISD-ELA, known as ELA before 2014) is an internationally unique research station encompassing 58 formerly pristine freshwater lakes in Kenora District Ontario, Canada. Previously run by Fisheries and Oceans Canada, ...
(ELA) in Ontario, Canada in the 1970s provided the evidence that freshwater bodies are phosphorus-limited. ELA uses the whole
ecosystem approach
The ecosystem approach is a conceptual framework for resolving ecosystem issues. The idea is to protect and manage the environment through the use of scientific reasoning. Another point of the ecosystem approach is preserving the Earth and its in ...
and long-term, whole-lake investigations of freshwater focusing on cultural eutrophication.
Terminology
Etymology
The term "eutrophication" comes from the
Greek
Greek may refer to:
Greece
Anything of, from, or related to Greece, a country in Southern Europe:
*Greeks, an ethnic group.
*Greek language, a branch of the Indo-European language family.
**Proto-Greek language, the assumed last common ancestor ...
''eutrophos'', meaning "well-nourished".
Other uses of the term
Terrestrial eutrophication
Whilst eutrophication is usually referring to aquatic systems, some authors have used the term "terrestrial eutrophication" for terrestrial ecosystems.
This is defined as "enrichment of an ecosystem with a limiting nutrient" and can be caused by nitrogen deposition on terrestrial ecosystems.
For example, atmospheric CO
2 fertilization can exacerbate the eutrophication of the
boreal forest
Taiga (; rus, тайга́, p=tɐjˈɡa; relates to Mongolic and Turkic languages), generally referred to in North America as a boreal forest or snow forest, is a biome characterized by coniferous forests consisting mostly of pines, spruc ...
biome.
See also
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External links
International Nitrogen Initiative
References
{{Authority control
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Nutrient pollution
Water pollution
Environmental chemistry
Environmental issues with water
Aquatic ecology