Nutrients is the general term given to certain compounds
essential for growth of living organisms. The most important of these are
nitrogen and phosphorus compounds. They are also excreted by living organisms
and can build up in the environment as waste products, food residues,
industrial and agricultural by-products, and contaminants. They can make their way into water ways by
run-off and other means. This can
contribute to the growth of photosynthetic aquatic micro and macro organisms
which can cause significant health and environmental issues.
All of the
forms of nitrogen described here are components of the nitrogen cycle and are
“Total Kjeldahl Nitrogen” (TKN) is a high temperature
acid-digest process that measures organic nitrogen and ammonia. Add nitrate and
nitrite (NOx) and we get what is termed “Total Nitrogen”.
- Ammonia (NH3)
occurs in natural waters and in wastewaters.
Ammonia is a component of the nitrogen cycle and is produced largely by
deamination of organic nitrogen-containing compounds and by hydrolysis of urea. Its concentration is generally low in
groundwater because it adsorbs to soil particles and clays and is not leached
readily from soils. At some water
treatment plants ammonia is added to react with chlorine to form a combined
- Nitrite (NO2)
occurs in natural waters, water distribution systems and wastewater treatment
plants as a result of chemical oxidation and reduction processes. Nitrite is an intermediate oxidation state of
nitrogen, being produced when ammonia is oxidised and when nitrate is being
reduced, and thus does not usually occur in large quantities or for very
long. Nitrite can enter a water supply
system through its use as a corrosion inhibitor in industrial process
- Nitrate (NO3)
also occurs in natural waters, water distribution systems and wastewater
treatment plants as a result of chemical oxidation and reduction
processes. Nitrate generally occurs in
trace quantities in surface water but may attain higher levels in some ground
waters. It is an essential nutrient for
many photosynthetic autotrophs and in some cases has been identified as the
Phosphorus occurs in natural waters and in
wastewaters almost solely as phosphates (PO4). Dissolved reactive phosphorus (DRP) is
analysed on the filtered part of a water sample.
At AST our
dissolved nutrients suite includes ammonia (NH3), dissolved reactive
phosphorus (DRP), nitrate (NO3), nitrite (NO2), and nitrate
+ nitrite (NOx). All of these analytes are reported as either mgN/L or mgP/L. We
utilise modern flow injection analyser (FIA) instrumentation for these
automated colourimetric analyses.
AST’s NATA-accredited low-level methods for environmental
monitoring programs deliver the following reporting limits:
|Reporting limit concentration (mg/L)
|±15% or ±0.005 mgN/L, whichever is greater
|±15% or ±0.002 mgN/L, whichever is greater
|±10% ±0.002 mgN/L, whichever is greater
|Nitrate + Nitrite (NOx)
|±15% ±0.002 mgN/L, whichever is greater
|Dissolved Reactive Phosphorus (DRP)
|±20% ±0.003 mgP/L, whichever is greater
|Total Kjeldahl Nitrogen (TKN)
|±23% ±0.10 mgN/L, whichever is greater
|Total Nitrogen (TN)
|±23% ±0.10 mgN/L, whichever is greater
|Total Phosphorus (TP)
|±28% ±0.01 mgP/L, whichever is greater
Recommended requirements for taking nutrient samples (sample
bottle types, preservation, filtration etc.) is available on our Nutrients
Silica (SiO2) is important to phytoplankton
communities. Silica is a food source for
zooplankton and filter feeders and can become depleted in waters if
eutrophication occurs. Silica can be also
be found in ground waters, depending on the parent rock material.
At AST we offer NATA-accredited SiO2 colourimetrically
by automated discrete analyser. Ideally samples should not be frozen before
analysis. Results are reported as mg SiO2/L with a reporting limit
of 0.1 SiO2/L. Measurement uncertainty for Silica has been calculated to be ±12% or ±0.05mg/L SiO2, whichever is greater.
Samples for silica analysis should be taken in a blue
labelled bottle or vial.
Nutrients in soils and sediments
AST offers NATA accredited nutrient analyses in soils, sediments, and biosolids. The tests on offer are similar to the waters suite: Ammonia, Nitrate, Nitrite, Nitrate + Nitrite, Total Kjeldahl Nitrogen, Total Nitrogen, Total Phosphorus, Bicarbonate extractable phosphorus, and water extractable Phosphorus.
We offer potassium chloride (KCl) extractions (1:10 or 1:5) or water extractions (1:10 or 1:5) for the nitrogen species, and bicarbonate extractions (1:100) or water extractions for phosphorous. The total nutrients analysis process comprises a high temperature acid-digest (Kjeldahl) followed by flow injection (FIA) automated colourimetric analysis. Other methodology may be accommodated or tailored for your specific requirements, please contact us if tailored analyses may be of use to your testing program.
Reporting limits for soil/sediment analytes vary, depending on the moisture content of the sample. Samples can be taken in glass sample jars and kept chilled while in transit to the laboratory.