Introduction to Nutrient Pollution

Introduction
On August 27, 2009 the State-EPA Nutrient Innovations Task Group issued an urgent call to action to EPA Administrator Lisa Jackson. The task group studied documented levels of excess nutrients in our nations waterways. Current, and past, efforts to control these pollutants have been inadequate on the national and statewide scale. Efforts to date have been predominantly “regulation at the pipe” and have not addressed the non point sources that are the root cause of elevated concentrations of nutrients in ground and surface waters. Nutrient pollution significantly impacts all of us. It impacts our drinking water, our recreational water, such as beaches and rivers and lakes, and it affects, and even kills, aquatic life. None of us want a bunch of dead rivers, but what can we do?
What are Nutrients?
Nutrients are elements that are essential to life. Being essential to life they are also essential components of the molecules that make up living tissue. Decaying organic matter and human and animal waste are significant sources of nutrient pollution in ground and surface water. The chemicals we manufacture and use in day-to-day life may also contain nutrients, as well as the fertilizers that we spread on our yards and farms. It is the broad application of fertilizers, the animal feeding lots, the widespread use of septic tanks, and runoff water from rainfall to school kid carwashes that are responsible for the immeasurable amounts of nutrients that find their way into the watershed. These are the non-point sources that cannot be easily regulated.
For 30 years the Clean Water Act has regulated industrial and municipal effluents. Limits are getting lower and lower. It is easy to take a sample at the end of a pipe. It’s easy to know where the sample comes from, and who is responsible if pollutants are too high. Unfortunately, 30 years of regulation of industry has not significantly reduced the problem. Obviously, there are other sources.
And the sources are us. Our everyday activities of washing our cars, fertilizing and watering our lawns, irrigating farms, and even desiring green golf courses. The essential nutrients that are in the fertilizers and detergents are entering the groundwater, not by an industrial effluent but down the gutter and into the storm drain. Rainfall is washing nutrients into creeks and rivers and carrying them into basins such as the Gulf of Mexico or Chesapeake Bay. Hypoxic zones, also known as dead zones, are forming where excess nutrients are deposited.
The excess nutrients cause a rapid growth of algae. The algae grow so rapidly that they cut off their own light and die. This is a normal, geologic process, occurring more rapidly than normal. As the algae dies it decays and the decay process consumes oxygen. Without oxygen aquatic life cannot breathe.
What is Nutrient Pollution?
Nitrogen and Phosphorus are the principal elements referred to when discussing nutrient pollution. Other essential elements, such as carbon, silica, and sulfur are not included in this discussion. Organic nitrogen and organic phosphorus are associated with the organic matter we measure and report as TOC. Nitrogen and phosphorus are essential elements in DNA, RNA, and nitrogen is a major component of protein and urine. Nitrogen and phosphorus occur as both water-soluble and water insoluble species. Unfortunately, both soluble and insoluble become bioavailable. Looking at this table, we see that Nitrogen and Phosphorus are somewhat similar chemically, for instance, the plus 5 ions known as nitrate and phosphate are very stable and highly water-soluble.
Nitrogen
Nitrogen is an essential nutrient for plant growth ranking only behind carbon, hydrogen and oxygen in total quantity needed. The nitrogen gas making up about 80% of the atmosphere is largely inert and unavailable to life directly. Lightning will convert small amounts of nitrogen to nitrate. Nitrogen in fertilizers largely comes from the chemical reaction between nitrogen and hydrogen gas to form ammonia. The ammonia can then be oxidized to form nitrate. Fertilizers will often contain ammonia, nitrate, and/or urea as the sources of nitrogen. Organic matter, referred to as humic matter, manure, mulch, etcetera contains about 5% Nitrogen. This nitrogen is slowly converted to ammonia by bacteria and is eventually oxidized to nitrite then nitrate. During a storm event, or during irrigation the nitrate in soil is easily leached into the runoff.
Dissolved inorganic nitrogen includes nitrate, nitrite, and ammonia. Dissolved organic nitrogen includes water-soluble proteins, amines, amides, and so forth. Basically decayed organic life and some man made chemicals that are dissolved in water. Total Organic nitrogen is the sum of dissolved organic nitrogen and particulate organic nitrogen. Particulate organic nitrogen is, well obviously, the insoluble organic compounds, or organic matter, in the water. Total Dissolved Nitrogen is the dissolved organic nitrogen plus the dissolved inorganic nitrogen, and Total nitrogen includes all of the above. Notice, there is REALLY no such thing as total inorganic nitrogen. This is because inorganic nitrogen compounds are all water-soluble.
Chemical Analysis of Nitrogen Compounds
Total dissolved nitrogen, or the result you get when analyzing total nitrogen on a filtered sample consists of dissolved organic nitrogen, nitrate, nitrite and ammonia. Methods used to determine TDN usually rely on an alkaline persulfate digestion that converts all of the nitrogen present to nitrate and then the nitrate is determined colorimetrically. Analyzing inorganic nitrogen alone will only recover about 30 – 40 % of the total dissolved nitrogen in the natural environment. Sewage treatment and industrial plant effluents, on the other hand, are predominantly inorganic nitrogen (nitrate) since the treatment process is designed to completely oxidize dissolved organic nitrogen and ammonia to nitrate.
Total nitrogen, or the result you get when analyzing total nitrogen on a non-filtered sample consists of dissolved organic nitrogen, nitrate, nitrite and ammonia plus particulate nitrogen. Since all inorganic nitrogen compounds are soluble, particulate nitrogen is almost entirely organic nitrogen, or PON. Methods used to determine TN can rely on the same alkaline persulfate digestion used to determine TDN with the exception that samples are not filtered. Since samples are not filtered, the automated version is not applicable if there is a significant amount of sediment (or solids) in the sample. In other words, the automated inline digestion methods measure TDN and are only applicable if TDN and TN are essentially equal (there is no particulate organic nitrogen).
The DIN fraction, measured to calculate the Total Organic Nitrogen content can be, and should be, analyzed on a filtered sample. Remember that there is no such thing as Total Inorganic Nitrogen since it is equal to Dissolved Inorganic Nitrogen. Another infamous parameter in the total nitrogen world is, of course, TKN (Total Kjeldahl Nitrogen). TKN, as routinely used, does not measure nitrate or nitrite. It is essentially a measure of organic nitrogen plus ammonia nitrogen.
TKN is the classical, if you will, analysis for total organic nitrogen. TKN has its roots in food and feed analysis as a way to quantify the amount of protein. TKN has been extrapolated to environmental analysis and is the regulated parameter for Total Nitrogen. Unless steps are taken to include nitrate and nitrite the regular TKN method does not measure it. TKN essentially measures organic nitrogen and ammonia. TKN is sufficient in POTW or municipal influents because these samples rarely have nitrate in them anyway. Recall the nitrogen reactions. An influent to a POTW will contain particulate nitrogen, dissolved organic nitrogen, and ammonia. The particulate nitrogen mostly settles as sludge removing it from the equation. Organic nitrogen and ammonia are oxidized to nitrate during the treatment process. The TKN digestion boils the sample in concentrated sulfuric acid in the presence of a metallic catalyst to speed the reaction. Potassium sulfate is added to raise the boiling point to about 380 C. The digestion will not completely recover all organic nitrogen compounds making the TKN result actually less than or equal to the TN determined by alkaline persulfate oxidation.
According to the EPA definition, Total Nitrogen equals TKN plus nitrate plus nitrite.
Phosphorus
Phosphorus is an essential nutrient found in living organisms as part of DNA among other important molecules. Phosphorus is always found in nature bound to other atoms and usually as the inorganic phosphate. It is phosphate that is available to plants and used as a fertilizer. It is phosphate that is consumed by algae and has the potential to cause algal blooms. Measurement of total phosphorus is important because it can, with time, convert to bioavailable soluble phosphate.

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Nitrogen and Phosphorus are the principal elements referred to when discussing nutrient pollution. Other essential elements, such as carbon, silica, and sulfur are not included in this discussion. Organic nitrogen and organic phosphorus are associated with the organic matter we measure and report as TOC. Nitrogen and phosphorus are essential elements in DNA, RNA, and nitrogen is a major component of protein and urine. Nitrogen and phosphorus occur as both water-soluble and water insoluble species. Unfortunately, both soluble and insoluble become bioavailable. Looking at this table, we see that Nitrogen and Phosphorus are somewhat similar chemically, for instance, the plus 5 ions known as nitrate and phosphate are very stable and highly water-soluble.
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