Nitrogen is an element needed by all living plants and animals to build protein. In aquatic ecosystems, nitrogen is present in many forms.
Nitrogen is a much more abundant nutrient than phosphorus in nature. It is most commonly found in its molecular form (N2), which makes up 79 percent of the air we breathe. This form, however is useless for most aquatic plant growth.
Blue-green algae, the primary algae of algal blooms, are able to use N2 and convert it into forms of nitrogen that plants can take up through their roots and use for growth: ammonia (NH3) and nitrate (NO-3).
How do aquatic animals obtain the nitrogen they need to form proteins? In two ways: they either eat aquatic plants and convert plant proteins to specific animal proteins, or they eat other aquatic organisms which feed upon plants.
As aquatic plants and animals die, bacteria break down large protein molecules into ammonia. Ammonia is then oxidized (combined with oxygen) by specialized bacteria to form nitrites (NO-2) and nitrates (NO-3). These bacteria get energy for metabolism from oxidation.
Excretions of aquatic organisms are very rich in ammonia, although the amount of nitrogen they add to waters is usually small. Duck and geese, however, contribute a heavy load of nitrogen (from excrement) in areas where they are plentiful. Through decomposition of dead plants and animals, and the excretions of living animals, nitrogen that was previously "locked up" is released.
There even exist bacteria that can transform nitrates (NO-3) into free molecular nitrogen (N2). The nitrogen cycle begins again if this molecular nitrogen is converted by blue-green algae into ammonia and nitrates.
Because nitrogen, in the form of ammonia and nitrates, acts as a plan nutrient, it also causes eutrophication. As you learned in the Total Phosphate Test, eutrophication promotes more plant growth and decay, which in turn increases biochemical oxygen demand. However, unlike phosphorus, nitrogen rarely limits plant growth, so plants are not as sensitive to increases in ammonia and nitrate levels.
Sources of Nitrates
Sewage is the main source of nitrates added by humans to rivers and lakes.
Sewage enters waterways in inadequately treated wastewater from sewage treatment
plants, in the effluent (outflow) from illegal sanitary sewer connections,
and from poorly functioning septic systems.
Septic systems are common in rural areas. Unlike large, centralized urban sewer systems that collect waste from many households, septic systems are generally used to treat the waste from only a single household.
In a septic system, household wastewater from toilets, sinks, bathtubs, and washing machines flows through a main pipe into a box called a septic tank. After larger waste materials settle and floating grease is skimmed off, the remaining liquid then flows through a grid of perforated pipes. The holes in these pipes allow the liquid to trickle out onto a layer of stone, gravel, and soil known as the "drain field".
In properly functioning septic systems, soil particles remove nutrients like nitrates and phosphates before they reach groundwater. However, two factors often keep septic systems from working like they should.
Septic systems must be properly located. When septic system drainfields are placed too close to the water table, nutrients and bacteria are able to percolate down into the groundwater where they may contaminate drinking water supplies. They may also find their way into lakes or rivers via groundwater flow.
Also, septic tanks must be emptied periodically, to function properly. If the tank is full, household wastes go directly to the drain field instead of settling in the tank. When this happens, the drain field pipes may become plugged, and household sewage may start to pool on the ground and enter water through surface runoff.
Water containing high nitrate levels can cause a serious condition called methemoglobinemia (met-hemo-glo-bin-emia), if it is used for infant milk formula. This condition prevents the baby's blood from carrying oxygen; hence the nickname "blue baby" syndrome.
Two other important sources of nitrates in water are fertilizers, and the runoff from cattle feedlots, dairies, and barnyards. High nitrate levels have been discovered in groundwater beneath croplands due to excessive fertilizer use, especially in heavily irrigated areas with sandy soils. Storm water runoff can carry nitrate-containing fertilizers from farms and lawns into waterways. Similarly, places where animals are concentrated, such as feedlots and dairies, produce large amounts of wastes rich in ammonia and nitrates. If not properly contained, these can seep into groundwater or be transported in runoff into surface waters.
As discussed in the Total Phosphate section, people have created the eutrophication problem that threatens to limit organism diversity, recreational opportunities, and property values. Only we can reverse eutrophication through thoughtful action.
Sampling Procedure
Again, any sampling device might be used for this water quality test to obtain
representative samples. It is also important to have spotless glassware, rinsed
with demineralized water. Always use demineralized water during the nitrate
test, Distilled water contains ammonia (NH3) ions that will interfere with
the test.
Nitrate Testing Procedure
Nitrate test kit items
Note: Use the following procedure for suspected nitrate nitrogen in the 0.25- 10.0 mg/L range. A low range test 0-1 mg/L Nitrate test is also available.
