Within the past 50 years, eutrophication, the over-enrichment of water by nutrients such as nitrogen phosphorus, has emerged as one of the leading causes of water quality impairment. The two most acute symptoms of eutrophication are hypoxia (or oxygen depletion) and harmful algal blooms, which among other things can destroy aquatic life in affected areas.


One of YouTube Videos on Eutrophication :

Figure 1: World hypoxic and Eutrophic coastal areas


Figure 2: Country freshwater ecosystem damage area from eutrophication in Europe from 1995 to 2010. Source: European Environment Agency (www.eea.europa.eu)

This divided body of water shows the difference between mesotrophic (moderately enriched, uper basin) and eutrophic water (lower basin)

Nutrient pollution from agricultural and urban non-point source run-off remains a major global problem - including many health-related implications.  Best management practices developed to control the non-point sources are not being widely implemented because of the lack of regulations that stems from the perceived higher costs of the most effective practices.  Harmful algal blooms have increased in freshwater and coastal systems over the last 20 years (Figure 4) [8] .  As algal toxins become concentrated in the fish and other marine organisms, they can cause fish and shellfish poisoning or paralysis.  Cyanobacterial toxins can also cause acute poisoning, skin irritation and gastrointestinal illnesses in humans.  The blooms (including red tides) have caused neurological damage and death in people through consumption of affected seafood [9].  
Table 1 summarizes the human well being and ecosystem impacts caused by increased nutrient levels.

Changes	Ecosystem impacts	Human well being impacts
		Human health	Food security	Socio-economic
↑ Nutrients	↑ Eutrophication	↑ Contamination of drinking water	↑ Production of macrophytes for animal fodder	↑ Cost of water treatment
	↑ Harmful algal bloom	↑ Fish and shellfish contamination ↑ Neurological and gastrointestinal illnesses	↓ Livestock health ↓ Food available for humans	↓ Recreational and tourism ↓ Livelihood income

The drivers of eutrophication are expected to increase for the foreseeable future.  
Specifically:

World population will continue to grow, reaching an estimated 9.2 - 10.6 billion by 2050 (UNESCO estimate in 2011), which will increase pressures on the productive capacity of agriculture and industry.
Intensive agriculture and land use conversion—for crops, livestock, and aquaculture—will increase, especially in the developing world.  In addition to population growth, intensification is driven by changing dietary patterns. For example, over the period from 2002 to 2030, global meat consumption is expected to increase by 54 %.
In general, fertilizer consumption is expected to increase 40 % between 2002 and 2030 [10]. The majority of the projected increase in global fertilizer consumption is attributed to the developing world where food production and adoption of intensive agricultural practices are expected to increase [10].  
As a result of these increasing global trends in population growth, fertilizer consumption and agricultural production, it is expected that coastal and freshwater systems impacted by eutrophication and hypoxia will continue to increase, especially in the developing world [6].

Virtually every living cell requires phosphorus. However, the soil from which plants obtain phosphorus typically contains only small amounts of it in a readily available form.  If soils are deficient in phosphorus, food production is restricted unless this nutrient is added in the form of fertilizer.  Hence, to increase the yield of plants grown for food, an adequate supply of phosphorus is essential.  Farming practices that are helping to feed billions of people include the application of phosphorus fertilizers manufactured from phosphate rock, a non-renewable resource used increasingly since the end of the 19th century.
Excessive P inputs: It is still not a common practice to account for input and output of chemicals in the environment (mass balancing, “budgeting”). The P budget of the upper Potomac River Basin revealed that over 60% of imported P was retained within the watershed [16]. In this case, P retention was caused by an excess of fertilizer and animal feed inputs over outputs of agricultural products.
In a Florida study, Fluck and colleagues (1992) [17] found that less than 20% of P input to the Lake Okeechobee watershed in fertilizers was output in agricultural and other products.
Some national and international studies reveal similar human impacts and increased P storage in terrestrial ecosystems. In every case, P accumulation was caused not by a natural imbalance in P inputs and outputs but by inputs of fertilizer and animal feeds that exceeded outputs in agricultural products [18,19]. P is flushing into the oceans: Based on the modern fluvial P flux, the amount of P discharged from the world’s rivers to the ocean, is estimated to be 22 Tg.yr-1 (1 teragram = 1 million metric tons) [20]. The agricultural P budget indicated that the average annual P accumulation in agricultural areas of the world was 8 Tg.yr-1 from 1958 to 1998. Increasing soil P levels elevate the potential P runoff to aquatic ecosystems [13].

P in brief:
About 4 % of mined P (1 Tg.yr-1) is used to manufacture products such as flame retardants, paper, glass, plastics, rubber, pharmaceuticals, petroleum products, pesticides, and toothpaste, which are not added to surface soils. Equivalent amount of mined P is also used to make calcium phosphate nutritional supplements for animals.
Current phosphate rock price is around $ 140 per metric ton (Figure 6). This means that annually, the amount of P discharged from the world’s rivers to the ocean is estimated at about $ 3 billion.yr-1. The amount of P accumulated in agricultural areas of the world is estimated at about $ 1.2 billion.yr-1.
The Commonwealth Scientific and Industrial Research Organization (CSIRO) in Australia has estimated that soils in that country alone contain 10 billion dollars of locked up phosphate that has been lost in this manner [21].
The eradication of hunger and poverty is Goal 1 of the Millennium Declaration, adopted by the United Nations General Assembly in 2000.  A 2010 review of progress towards achieving the Millennium Development Goals reported that hunger and malnutrition increased between 2007 and 2009, partially reversing earlier progress [25].  Many of the world’s estimated 925 million undernourished people are small-scale farmers.  Phosphorus-based fertilizers are often unobtainable by these farmers, whose productivity could be improved with better access to this input [26].

While there are commercially exploitable amounts of phosphate rock in several countries, those with no domestic reserves could be particularly vulnerable in the case of global shortfalls (Table 2).


Figure 5: Peak phosphorus curve based on industry data, indicating a peak year of global phosphate rock population in 2033 [22].


The annual production of phosphate rock in 2005-2010 is around 24 Tg.yr-1. More than 90 - 95 % of rock phosphate is used for fertilizers.

The known supply of cheap, high-grade reserves of phosphate rock is becoming increasingly limited while demand continues to increase.  The remaining amount of commercially viable phosphate rock, particularly the lifetime of reserves, has been the subject of vigorous debate among experts during the last few years.  For example, Cordell et al. (2009) [22] estimated that peak production of current reserves (that is, phosphate rock known to be economically available for mining and processing) would occur between 2030 and 2040 (Figure 5).  The most recent USGS reserves estimates have been revised upward [23], from 16 to around 60 billion tons of phosphate rocks.
Proponents of the peak phosphorus theory argue that even if the timeline may vary, the fundamental issue, that the supply of cheap and easily accessible phosphorus is ultimately limited, will not change.
New phosphate rock mines have been commissioned in several countries, including Australia, Peru and Saudi Arabia, while undiscovered deposits are being widely sought, including in seafloor sediments off the coast of Namibia [24].

Although estimates of the extent of known reserves are increasing, the quality of these reserves requires further evaluation. If the phosphate concentration in the rock declines and larger volumes of ore are needed in order to obtain a given amount of phosphorus, production costs will likely increase.  Such changes could also lead to greater energy requirements and more waste in phosphate rock mining. In an open market these factors might well raise the price of phosphorus fertilizers, limiting their accessibility to many farmers and having negative effects on yields.  If these were to occur, food security could be threatened in countries that are highly dependent on phosphorus imports.