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Phosphorus

Nitrogen

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Phosphorus

Phosphorus is an important nutrient as it is the limiting element necessary for the growth of plant life. Below is the amount of of carbon, nitrogen, and phosphorus atoms required within an environment to induce plant growth. Notice how only one phosphorus atom is required in this ratio? This is because phosphorus is the limiting reagent, meaning that it is the least required substance for photosynthesis (the process of plant growth) to occur. This makes phosphorus the most important element in this ratio, since an environment with limited phosphorus means there will be limited plant growth, however, an environment with excess phosphorus will cause a proliferation of plants.

106 C:16 N:1 P

Phosphorus can be sourced from many areas in the environment, with some examples of natural sources being from decomposing leaves, stream sediments, eroded soil sediments, algae, or animal remains. Alternatively, phosphorus can originate from man-made sources such as fertilizers, mining of phosphate minerals, or cattle manure.

Despite phosphorus being essential for plant growth, excess amounts can cause negative environmental impacts such as eutrophication.

Eutrophication: The result of large amounts of nutrients being released into a nutrient deficient water body which leads to an excessive amount of aquatic plant growth

Eutrophication results in the growth of algal blooms which are algae and cyanobacteria that can grow to long lengths within waterbodies. The overgrowth of these algal blooms can cause:

• Blockage of sunlight for underlying aquatic life
• Reduced dissolved oxygen (hypoxic conditions) within waters causing aquatic life to die off
• Release of harmful toxins into waterbody from blue-green algae causing health problems for human and aquatic organisms

Nitrogen

Nitrogen is an important nutrient for the growth of plants and can be present in the environment in different molecular forms: nitrate, ammonium, ammonia, nitrous oxide. However, excess amounts can cause imbalances in the environment and cause harmful environmental impacts to ecosystems. Nitrogen can be sourced from both natural and man-made processes in the environment. Natural sources include the release of nitrogen from decomposing organic matter (e.g. plants, animals, manure) or from rainwater that contains soluble nitrogen within it. Man-made nitrogen inputs to the environment are the largest contributors and predominantly come from the agricultural industry and industrial air pollution.

Agricultural fertilizers are used to assist with plant growth of crops but is problematic since many fertilizers contain high concentrations of synthetically made nitrogen within them. Once fertilizers are applied to agricultural fields they can infiltrate into underlying groundwater systems within the soil or runoff into nearby streams or lakes, potentially causing eutrophication. As mentioned in the Phosphorus section, eutrophication refers to the excess input of nutrients into a water system that causes the rapid growth of nuisance plants (algae). This process can cause environmental harm by reducing oxygen availability for aquatic organisms, introducing potentially toxic forms of algae, and blocking out sunlight that is essential for aquatic organisms to survive. Within the agricultural industry, nitrogen can also be sourced from cattle manure or crop residues. Another major nitrogen source in the environment is from soil emissions, in which microbes within the soil are constantly converting nitrate within the soil into nitrogen gas (denitrification process) that gets released into the atmosphere.

As previously mentioned, excess concentrations of nitrogen within the environment can cause harmful impacts such as eutrophication. However, high concentrations within water that is ingested can impact human health and cause methemoglobinemia, which is a condition that can occur in infants and impact the blood circulatory system and potentially be life-threatening. Nitrogen can further be impactful on the environment due to one of it's gaseous forms (N₂O), which is a potent greenhouse gas. Refer to the N₂O section to further learn about the impacts of nitrous oxide.