Eutrophication
[1] Additionally, the introduction of bacteria and algae-inhibiting organisms such as shellfish and seaweed can also help reduce nitrogen pollution, which in turn controls the growth of cyanobacteria, the main source of harmful algae blooms.
[7] Thus, eutrophication has been defined as "degradation of water quality owing to enrichment by nutrients which results in excessive plant (principally algae) growth and decay.
[9] Breakthrough research carried out at the Experimental Lakes Area (ELA) in Ontario, Canada, in the 1970s provided the evidence that freshwater bodies are phosphorus-limited.
[13] The limitation of productivity in any aquatic system varies with the rate of supply (from external sources) and removal (flushing out) of nutrients from the body of water.
[23] 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.
[25] 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.
[27] The deterioration of water quality caused by cultural eutrophication can therefore negatively impact human uses including potable supply for consumption, industrial uses and recreation.
Algal blooms limit the sunlight available to bottom-dwelling organisms and cause wide swings in the amount of dissolved oxygen in the water.
Human health effects of eutrophication derive from two main issues excess nitrate in drinking water and exposure to toxic algae.
[51] Getting direct contact with toxic algae through swimming or drinking can cause rashes, stomach or liver illness, and respiratory or neurological problems .
[52] One response to added amounts of nutrients in aquatic ecosystems is the rapid growth of microscopic algae, creating an algal bloom.
[53] Nutrient pollution 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.
The dead algae and organic load carried by the water inflows into a lake settle to the bottom and undergo anaerobic digestion releasing greenhouse gases such as methane and CO2.
[54] Thus a self-sustaining biological process can take place to generate primary food source for the phytoplankton and zooplankton depending on the availability of adequate dissolved oxygen in the water body.
[55] 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 which is needed for fish and shellfish to survive.
[57] Phosphorus is often regarded as the main culprit in cases of eutrophication in lakes subjected to "point source" pollution from sewage pipes.
[61] 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.
Examples of anthropogenic sources of nitrogen-rich pollution to coastal waters include sea cage fish farming and discharges of ammonia from the production of coke from coal.
[62] 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.
[65][66] A third key nutrient, dissolved silicon, is derived primarily from sediment weathering to rivers and from offshore and is therefore much less affected by human activity.
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.
For example, sewage treatment plants can be upgraded for biological nutrient removal so that they discharge much less nitrogen and phosphorus to the receiving water body.
Some recommendations issued by the U.S. Department of Agriculture include:[78] The United Nations framework for Sustainable Development Goals 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 (life below water).
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.
[18] In environmental remediation, nutrient removal technologies include biofiltration, which uses living material to capture and biologically degrade pollutants.
[89] Shorter term predictions can help to show the intensity, location, and trajectory of blooms in order to warn more directly affected communities.
[93][94][95] Filter feeding activity is considered beneficial to water quality[96] 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.
[97][98] Foundational work toward the idea of improving marine water quality through shellfish cultivation was conducted by Odd Lindahl et al., using mussels in Sweden.
