General Purpose
Conceptual
Procedural
Chemical reactions are required for many abiotic factors to be analyzed. In this pre-lab, the assays for phosphate and various forms of nitrogen in the nitrogen cycle will be explored.
Phosphate is an essential nutrient for both heterotrophs and autotrophs. Phosphate is often the limiting nutrient in freshwater systems. A normal level of phosphate is around 0.05 mg/mL. Poor water quality in many lakes and aquatic ecosystems can be partly due to accumulated phosphate in the bottom sediments. Excessive phosphate can result in excessive algae growth (algae blooms) which is one cause of the fish kills the University Lake system periodically experiences. Algae blooms can release toxins, block sunlight, thus reducing lake autotrophs, and reduce dissolved oxygen. Phosphate occurs naturally in rocks and soil. Sources of excess harmful phosphate are fertilizers, animal feed, animal waste and sewage.
The following chemical forms of the nitrogen cycle can impact the organisms in an ecosystem.
Ammonia/Ammonium (NH3/NH4+): Ammonia and the protonated form ammonium are soluble in water. Nitrogen-fixing bacteria convert nitrogen gas to ammonia. This form of nitrogen can be used by many organisms. Ammonia results from metabolic waste and fungal or bacterial decay of organic material. Nitrogen fertilizers introduce ammonia into the environment.
Nitrite (NO22−): A short-lived form of nitrogen intermediate between ammonia and nitrate. Chemotrophic bacteria convert ammonia to nitrite, and then other species of bacteria convert nitrite to nitrate.
Nitrate (NO3−): The form of nitrogen that is most usable by plants, where it can be converted to nitrogen-containing amino acids for use by heterotrophs.
Both ammonium and nitrate can be introduced into the aquatic ecosystem by runoff water entering the watershed. Both are components of common commercial fertilizers and ammonium (from ammonia) can also result from animal feces (directly in the water or as runoff).
The presence of nitrite is indicative of bacterial activity because the main source is conversion of ammonium into nitrite by various microorganisms in the ecosystem.
Nitrite analysis (like many water analyses) requires a chemical reaction which gives a color product that is proportional to the amount of nitrite present in the sample. Most of these chemical reaction assays involve chemicals that can be harmful so the appropriate precautions (gloves and eye protection) should be used. Also, if the colorimetric reaction is judged by eye, then the same person should be the judge for each of the same type of assays.
Please view the following video to see some of the aspects of the nitrite test.