Nutrient Pollution: Causes & Consequences:
Introduction:
Nutrients are naturally occurring chemicals, most commonly compounds of nitrogen, or “fixated” nitrogen, which are essential to the growth of plants of all kinds. As with anything of value in complex organic systems, however, there is an optimum amount of nutrients in the biosphere. Both too much or too little are bad for the system as a whole.
Thus, nitrogen, in its various compound forms, is a naturally occurring chemical within the biosphere. In fact, the amount of available nitrogen is one of the limiting factors concerning the productivity of ecosystems, because it limits the growth of the plants, which are at the base of the food chain.
Under natural conditions nitrogen is “fixated” into more complex compounds both by lightening strikes in the atmosphere, and by bacteria breaking down complex organic material in the soil. Various human activities, however, are altering the nitrogen cycle both through artificial fixation and the concentration of organic material.
Sources of nutrient pollution:
In addition to natural fixation, there are also various artificial sources of nutrients, which are adding to the problem of nutrient pollution, especially by artificially inflating nutrient levels beyond their optimum range. These include:
1. Artificial fertilizers applied to agricultural crops. Most crops are now nutrient saturated, and because artificial fertilizers are so cheap, they are often over-applied. This implies that the excess which is not taken up by the plants they are applied to (be they agricultural crops, the lawn in your yard, or at the golf course) are washed away into rivers, streams and ground water.
2. Concentrated sewage. The concentration of both animal wastes from intensive livestock production and the concentration of human wastes from urbanization also lead to concentrated nutrient pollution. Sewage is often dumped directly into surface waters, spread in too great a concentration on soil, or seeps into groundwater.
3. Combustion. All forms of combustion, particularly that of fossil fuels such as coal, oil and natural gas, also contribute to nutrient pollution. The same is true of wood burning, ethanol, biodiesel and other biologically based fuels. This is because combustion releases nitrogen oxides, or NOx (NO, NO2, NO3) into the atmosphere, also contributing to nutrient pollution.
All of these processes (and others to a lesser extent) feed back into one another, artificially increasing the amount of nitrogen compounds in the biosphere, well beyond their optimum range ecologically. The potential ecological and human health effects of are well documented.
The Principle Effects of Nutrient Pollution:
1. Human Health Effects:
Human health effects are largely due to the contamination of groundwater or other drinking water with elevated levels of nitrates. According to Danielle Nierenberg (2001), this can lead to both elevated risks of miscarriage for pregnant women and to “blue-baby syndrome.” Also known as “methemoglobinemia,” blue-baby syndrome results from the fact that human infants’ digestive systems convert nitrate to nitrite. The problem is that nitrite blocks the blood’s oxygen carrying capacity. The result is suffocation and death. Ruminant livestock such as cattle, sheep and goats, whose digestive systems behave in a similar way, are also vulnerable. Over 3,000 babies have died from blue-baby syndrome world wide since 1945 (Sampat 2000).
2. Effects on Vegetation:
Just as too few nutrients are bad for plants and limit their ability to grow, too much is also detrimental. As Payat suggests, too many nutrients actually weaken plants immune systems, making them more vulnerable to pests and disease (2000). The immune systems of plants are very different from those of animals. This is because they are based upon the production of a number of chemicals to neutralize toxins and disease, instead of the production of killers cells and antibodies. Excess nutrients interfere with the natural production of these chemicals and, as Chris Bright describes it, can lead to “a kind of botanical equivalent of AIDS” (1999).
Excess nutrients can also reduce cold hardiness in some species, and restrict the uptake of water and soil nutrients in others (Nierenberg 2001).
3. Effects on Surface Water:
Besides the risks to human health associated with ground water pollution, nutrient pollution also affects surface waters and the health of the wildlife they contain.
A. “Red tide” organisms are toxic forms of algae in the ocean. Being a type of plant, excess nutrients can lead to an explosive growth in the population of such species to the extent that their toxins lead to fish kills.
B. “Eutrophication” events can lead to fish kills as well. Besides red tide organisms, nutrient pollution of water bodies also promotes the growth of algae in general. Algae, after all, are merely microscopic forms of plant life which live in bodies of water, and they respond to an increase in nutrients in the same way that a crop of wheat or corn does-by growing more quickly.
If nutrient levels from agricultural run-off, or from high levels of organic wastes or sewage more generally, become too high, they can lead to a process known as eutrophication. Eutrophication happens in two stages:
First, increased nutrient levels cause an explosive growth of algae in bodies of water.
Second, as these unnaturally high populations of algae die and begin to decay, their decay consumes all of the oxygen content in the water, killing fish and all other oxygen dependent species.
The process is rather paradoxical, since plants give off oxygen, but the process of decay consumes more oxygen than they give off. There have even been documented cases of eutrophication events in coastal waters in the ocean after heavy spring rains cause large amounts of nutrients to be washed into the sea.
Nutrient pollution also contributes to the decline of corral reefs in many areas, which are the most ecologically diverse marine ecosystems (as rain forests are for terrestrial ecosystems).
In general, what nutrient pollution does is to artificially alter the nitrogen cycle, which can lead to an imbalance between the plant and animal life in bodies of water, which causes the larger ecosystem to collapse, either temporarily in the ocean, or more permanently in smaller bodies of water.
Conclusion:
Nutrient pollution is a global problem. The effects on forests, water and fish are particularly central. The solutions are fairly simple.
1. Convert from fossil fuels to alternative energy sources, such as hydrogen fuel. Hydrogen fuel can be produced by the electrolysis of water, and when utilized through a fuel cell, can provide a completely emission free source of energy which does not require combustion (and therefore produces no nitrogen oxides). I am sure you can find articles on the hydrogen economy elsewhere on Helium.
2. Eliminate the use of artificial fertilizers, which add excessive nutrients to the nitrogen cycle, and replace artificial fertilizers with human and animal wastes.
This solves two problems at the same time, since sewage is a natural fertilizer which is currently problematic only because it is both concentrated in centralized locations, and /treated/ as “waste.” If it were treated as the natural fertilizer which it is, and spread thinly over the landscape instead of being concentrated in centralized locations, it would not be problematic.
Human sewage, in particular, would have to be separated from the various toxins (household cleaners, etc.) which we flush down our drains, and from industrial water, in order to prevent the contamination of soils and crops. But sewage in and of itself is a naturally occurring source of nutrients in the biosphere.
In sum, solving the global ecological problems associated with nutrient pollution can be achieved by limiting food production to the natural productivity of the land, treating sewage as the resource which it is, and limiting fossil fuel consumption.
References, additional reading:
Chris Bright (1999) “The Nemesis Effect,” World Watch, May/June.
Danielle Nierenberg (2001) “Toxic Fertility,” World Watch, March/April.
Payal Sampat (2000) “Groundwater Shock: The Polluting of the World’s Major Freshwater Stores,” World Watch, January/February.
