4.7. Contaminants and Eutrophication
Contamination is the presence of elevated concentrations of substances in the environment above the natural background level for the area and for the organism. This includes visible litter as well as invisible waste such as chemicals from personal care products and pharmaceuticals that we flush down our toilets and drains. Once in the sea, these pollutants can move through the ocean, endangering marine life through entanglement, ingestion and intoxication. Pollution by chemical substances is of concern for the maintenance of healthy and sustainable marine environment.
Problems related to chemical contamination of the aquatic environment are nearly all man-made. Effluents from aquaculture ponds, agriculture runoff, sewage discharge, toxic effluents from industry into the contiguous water body, all affect the marine environment through biological, chemical and physical interactions over different temporal and spatial scales. In addition there may be impacts that arise as a consequence of accidents or failure of normal operations such as oil spills in coastal waters.
Sources of different contaminants are various and often difficult to track. Contaminants reach the marine environment mostly directly from land-based sources, but there are cases in which they are emitted or re-mobilized in the marine environment itself. Some studies have shown that the main sources of pharmaceuticals and artificial food additives in Mediterranean are runoffs from agricultural areas but also some offshore sources such as ferries and cruising ships.
Some pollutants resist breakdown and accumulate in the food chain. These pollutants can be consumed or absorbed by fish and wildlife, which in turn may be eaten by us. Chemicals can also get into sediments, impacting large coastal areas, threatening human health, and reducing the economic well being of regions that depend on a healthy coastal environment.
Due to incorrect disposal, plastic debris can be found in seas and oceans all over the world. Ingestion of the smaller parts by marine birds, turtles and mammals has been reported by various researchers. Ingested plastic particles can potentially reduce food uptake, cause blockage of the digestive tract, and be a source of contaminants like PCB’s. Additionally, sea salt around the world has been contaminated by plastic pollution, adding to experts’ fears that microplastics are becoming ubiquitous in the environment and finding their way into the food chain via the salt in our diets.
A different, but linked, phenomena we can observe in our sea is the eutrophication, the process of enriching water with nutrients, resulting in increased primary production. High concentrations of nitrogen and phosphorus nutrient salts are resulting in excessive propagation of phytoplankton, and thus the production of organic matter above the degradation capacity of the ecosystem. Increased aquatic plant production results in an increased content of organic matter that is broken down by bacteria, producing unpleasant smells, consuming the available oxygen, and influencing the development of other water organisms.
Excessive production of organic substances significantly increases the consumption of dissolved oxygen with serious consequences for benthic organisms. Particularly in the summer period, dissolved oxygen deficiency can occur in the bottom layer (anoxia), along with a mass disappearance of the ubiquitous, especially immobilized organisms. There may be changes in the composition of the community due to the higher share of species that are less useful for the food chain and ultimately multiply the organisms whose metabolic products are toxic. Typical indicators of eutrophication of the marine environment are low transparency, supersaturation with oxygen in the surface layer and hypoxia / anoxia of the sediment, high concentrations of nutrients and large planktonic biomass.
Eutrophication can be natural or can be caused by human activities due to excessive release of nutrients into wastewaters. Natural eutrophication is positive for the ecosystem due to the increase of biological resources, with rare adverse events. On the other hand, human activities such as washing the farm surface with massive use of artificial fertilizers or inappropriate disposal of sewage into the sea can disturb the ecological balance with very damaging consequences for the local ecosystem.
One of the negative consequences caused by eutrophication is phenomena known as harmful algal blooms (HABs). It occures when colonies of algae under the right conditions, grow out of control. Few of these “blooms” produce toxins that can kill fish, mammals and birds, and may cause human illness or even death in extreme cases. Other algae are nontoxic, but eat up all of the oxygen in the water as they decay, clog the gills of fish and invertebrates, or smother corals and submerged aquatic vegetation. Still others discolor water, form huge, smelly piles on beaches or contaminate drinking water. Collectively, these events are called harmful algal blooms, or HABs.
4.7.1 What is contamination?
Contamination is the equivalent of pollution, where the main interest is the harm done on a large scale to humans or to organisms or environment which are important to humans. In fact there is a change in the ecosystem which is caused by natural or artificial input of dangerous contaminants into the environment, and may cause instability, disruption or other negative effects to the system. Some examples of natural causes can be living organisms like bacteria, enzymes, viruses or their products while artificial ones can be personal care products and pharmaceuticals.
There are different ways for the contaminants to reach the marine environment. Usually they originate from land-based sources, but sometimes they are emitted or re-mobilized in the marine environment itself. There are different causes for contamination. The main sources are treated and untreated waste water, due to port activities and industrial activities, which are dangerous because they are difficult to isolate and to eliminate and have a long lifetime. These substances are found frequently in seas and they are hazardous because they are the cause of the contamination of seafood which is consumed by a large part of the population.
Another problem related to contamination is the pollution of the water sources situated under the earth, caused by insecticides used in the fields.
After giving a definition of contamination, we can explain the difference between contamination and pollution. Contamination is the presence of a substance which should not be present naturally and pollution is when the contaminants damages organisms or structures in the nature.
4.7.2 Sources of chemical contamination of the sea
There are a lot of sources of chemical contamination and they are not always easy to track.
Problems related to chemical contamination of the aquatic environments are nearly all man made.
Human activities produce an infinite number of chemical substances, which released into the environment, can produce unwanted or harmful effects that are sometimes immediate, but much more often due to continuous little accumulations can cause medium and long-term significant alterations of the water bodies of the receptors and the quality of waters.
The main sources are effluents from aquaculture ponds, agriculture runoff, sewage discharge, toxic effluents from industry.
The most frequent chemical substances subjected to industrial pollution are: acids and alkalis, chlorine, ammonia, hydrogen sulphide, heavy metals.
To these are added pollutants such as oils and detergents that can compromise the passage of solar radiation into the aquatic environment and, consequently, interfere with the life cycles of plant and animal microorganisms.
Moreover, non-degradable pollutants, I. e. substances and poisons such as synthetic polymeric materials, aluminum cans, some mercury compounds, chemical substances with long side chain phenolic radicals, DDT and PCBs, which are not degraded, or which are degraded very slowly in the environment, are sources of chemical pollution.
Hydrocarbons are also an example of chemical pollution. These can form thin films on the surface of the water that are oxidized to light and biodegraded, at least partially, by bacteria, yeasts and filamentous fungi, causing immediate repercussions on organisms because the thin oily veil can hinder the passage of solar radiation.
In addition, plastic debris are all over the world and microplastics can be found in sea salt.
Another kind of chemical contamination originates from ferries and cruising ships.
4.7.3 How can contamination of the sea influence human health?
Contamination of the sea is a big issue that puts in danger both aquatic life and terrestrial life. Most of the sea contamination is caused by human activities, such as aquaculture ponds, agriculture runoff, sewage discharge and toxic effluents from industries.
Everything we throw in the sea comes back to us like a boomerang. All the effluents are absorbed by the sea creatures that we will fish and sell on every super-market or fishmongers.
Moreover, chemicals can get into sediments and threaten human health in a less direct way; while we are ruining our health we are ruining fish's one too. Little pieces of plastic are ingested by marine birds,turtles and mammals. In addition, micro plastic is contaminating sea salt thus we are eating plastic too.
Another argument is that the rubbish that accumulates near touristic points ruins the beaches, harbours and nature locations, which are source of income for many people. Plastic can destroy an entire habitat and the economy of an entire city.
If contamination is so dangerous why aren't we stopping it? That's because tracking contaminants, which are thousands, is extremely difficult as they reach the sea not only from the land, but also directly from sea floor.
In conclusion sea contamination represents a hazard for the human health, and even without the other problems it causes this should be enough to make everyone aware of the danger sea contamination and that it should be dealt with as soon as possible in order to have a better life.
4.7.4 Name three sea animals that are directly endangered by plastic debris in the sea!
Plastic bags look very similar to jellyfish and nets often look like tasty seaweed. Sea turtles think that they are consuming some of their foods but they are welcoming harmful substances into their stomach. Now all species are used to treat of sea turtle are classified as endangered, and plastic is doing more than its share of damage. Plastic can cause, in the sea turtles, the block of their intestines and then their death. The turtles are strong swimmers, they often become entangled in fishing gear, and they are weighted down. Globally it's estimated that approximately 52% of all sea turtles have eaten plastic. As for marine mammals, it's estimated that 56% of planet's whales and dolphins have consumed plastic. A plastic bag looks like a squid or other pray. Some scientists believe that unnatural objects such as plastic waste are incorrectly interpreted as by dolphin or whale's sonar . The number of seabirds dying as a result of plastic is currently estimated at 1 million a year. This shocking statistic becomes even more worrying when we consider just how quickly this problem has grown. Since plastic debris provides an ideal platform for algae development, the birds mistake the plastic fragments on which the algae cling to krill, and swallow them.Then ,tragically, adult birds that leave nests to hunt often return with plastic they have mistaken for food and feed it to their chicks. The juveniles' smaller stomachs are even less able to deal with the effects of the plastic and many don't make it to adulthood.
4.7.6 Describe eutrophication!
Eutrophycation, comes from the Greek word eutrophos, "well sustained".
Eutrophication is a process that happens when the water becomes over saturated with minerals and nutrients which cause excessive growth of marine plants and algae. This process may end up in a lack of oxygen in the water caused by the consumption of oxygen during the degradation of the biomass of these dead organisms. Eutrophication is pretty much always caused by the pollution of the water, the nitrates or phosphates contained in detergents, fertilizers, sewage and other various chemicals. An example can be the increase of phytoplankton as a response to the eccessively high levels of nutrients. The worst consequences of eutrophication is the creation of dense blooms of foul smelling phytoplankton that unfourtenatly reduces water clarity and harms the waters quality. Algal blooms usually limit light penetration, reducing growth and causing the death of plants in littoral zones while also lowering the success of predators that need a certain amount of light to follow and catch their prey. Also high rates of photosynthesis can deplete dissolved inorganic carbon and raise pH levels during the day. This can result in the death of organisms that rely on perception of dissolved chemical for their survival. When these dense algal blooms finally die, microbial decomposition severely depletes the oxygen, creating a hypoxic zone lacking sufficient oxygen to support most organisms. In the 1960s and '70s, the eutrophication of Lake Erie advanced so extremely that it became known as the "dead lake".
In summary the main causes are human made substances that start these kinds of natural disasters.
4.7.7 What are the main consequences of eutrophication in the sea?
The term eutrophication indicates a condition of nutrient richness in a given environment, in particular an overabundance of nitrates and phosphates in an aquatic environment.
The term is also commonly used to indicate the excessive growth of plant organisms, due to the presence in the aquatic ecosystem of too high doses of nutrients such as nitrogen, phosphorus or sulphur, coming from natural or anthropogenic sources.
The accumulation of elements such as nitrogen and phosphorus causes the proliferation of microscopic algae which, in turn, not being disposed of by primary consumers, determine a greater bacterial activity; in this way the global consumption of oxygen increases, and the lack of oxygen causes the death of fish in the long run.
Eutrophication of the sea leads to some quite disastrous effects:
reduction of species diversity and mutation of dominant biotics, increase in animal and plant biomass, increase in turbidity and foul smell of water, decrease in the amount of oxygen in the water and increase in aquatic plants near the coasts.
To counteract eutrophication, interventions are needed to reduce nutrient inflows to water bodies (reduction of fertilizers in agriculture, purification of civil and industrial waste, treatment of crop wastewater through sequestering agents and phytodepuration plants). Global warming is expected to contribute to worsening the phenomenon of eutrophication. The heating of surface waters, in fact, decreases the solubility of gases and therefore also of oxygen.
4.7.8 Which are the typical indicators of eutrophication in the sea?
The eutrophication is a process linked to water contamination that happens when a body of water becomes full of nutrients, like mineral salts. An high concentration of these substances results in an overgrowth of phytoplankton, bacteria, fungus and seaweeds that leads to several problems in the sea ecosystem, usually shortage of oxygen, fish kills, human health disease and general degradation of water characteristics, like smell or colour. In fact, algae grow on the sea floor, where sun's rays don't arrive. Without solar energy algae die and bacteria start decomposing them. But to do this they need oxygen, that is taken from the water, causing lack of oxygen under the surface (this reaction is called anoxia) and fish die-off.
The main causes of this phenomenon are linked to the impact of human activities on the environment, although there are special cases when it's caused by natural events. The land runoff, that increases nutrients (specially nitrogen and phosphorus) level of the water, is accelerated by agriculture activities, use of fertiliser and discharge of water and waste substances deriving from industries into watercourses.
To recognise the presence of eutrophication there are some indicators that allow us to identify it. These are: turbidity of the water, excessive saturation of oxygen in the surface and anoxia in the sea bed, high concentrations of nutrients, like Chlorophyll a (indispensable for algae), absence of biodiversity and large brown, green, red or yellow planktonic and cyanobacteria biomasses.
The eutrophication represents an extremely dangerous process which could become more and more widespread, bringing to higher fish mortality, water toxicity and the destruction of marine and terrestrial ecosystems.
4.7.9 Harmful Algal Blooms (HABs)
Many times, people who are at the beach and want to swim in the sea must give up their intention as the water is full of smelly algae, which they certainly find unpleasant. These colonies of algae that grow out of control while producing toxic or harmful effects for humans, fish, shellfish, marine mammals and birds are called HABs (Harmful Algal Blooms). Although also warm water temperatures (increased by climate change) and water flow play a role in their growth, the main cause is eutrophication, which results in enriching water with nutrients such as nitrogen and phosphorus that can lead to changes in the food chain. The sources of the nutrients are identified with agricultural and aquaculture discharge that flows into bays, rivers and seas, like fertilizers. As the blooms grow, they consume the available oxygen, which concentration decreases due to their respiration during the night, and they prevent sunlight from reaching fish and other plants. Besides, when the algae die, which can happen within a few days or a few months, the bacteria that decompose them use up even more oxygen. This leads to the creation of anoxic (lacking oxygen) dead zones, where neither fish or aquatic vegetation can survive: animals’ gills are clogged, corals are smothered. The disappearance of little organisms in the bottom layer due to anoxia negatively affect the development of water organisms, which become less useful for the food chain, multiplying organisms whose metabolic products are toxic. Some algae produce toxins, too. They’re called “Microcystis” and once ingested, they can have debilitating effects for both fish and humans, such as shellfish poisoning. Fortunately, not all algal blooms are harmful, with some only discolouring water and producing a smelly odour; these ones don’t affect animals or people health, but they have a negative influence on the economic wellbeing of coastal regions. Experts are running studies about HABs, but still haven’t found a solution yet.