Nutrients are essential for life in the water and on land. But too much nutrients (Eutrophication) is harmful. Important nutrients include the nitrogen compounds nitrate (NO3-), nitrite (NO2-), ammonia (NH3) and ammonium (NH4+). Sometimes it is important to measure it separately, but sometimes the total nitrogen (Total-N) is important. Another important nutrient is phosphate (short for orthophosphate, PO43−). Instead of specifically measuring phosphate, sometimes the total phosphorus (Total-P) is important.

Some of the nutrients mentioned can be measured with so-called ISE (Ion Selective Electrode) sensors, see the ‘multiparameter measuring sondes’ category . The advantage of these sensors is that they can be used relatively cheaply and quickly. However, because the calibration expires in short span of time, these sensors need to be calibrated frequently and are therefore mainly suitable for hand measurements and for detecting ‘incidents’ (short-term disturbances) and less for continuously measuring and determining trends.

Accurate measurement of nutrients is very important, but requires high-quality measuring equipment. For that purpose Observator offers instruments from Xylem/YSI, Systea and TriOS:

• The Xylem/YSI ISE probes for ammonium and nitrate, for use with EXO sondes and the ProDSS handheld.
• The Xylem/YSI NitraLED UV Nitrate Sensor with state-of-the-art LED technology, for long-term nutrient monitoring, for use with EXO sondes.
• The Systea WIZ probe: The WIZ probe is a kind of ‘mini-lab’ with which the concentration of a large number of substances can be measured fully automatically (in the field). Substances such as: nitrate, nitrite, ammonia, phosphate. Nitrogen (total) and phosphorus (total) and various other compounds can also be measured. The WIZ is suitable for both freshwater and saltwater.
• The TriOS OPUS sensor: The OPUS measures the absorption of 256 spectral lines and calculates the concentration of a number of compounds, including nitrate and nitrite. The OPUS is suitable for both freshwater and saltwater.
• The TriOS NICO sensor: The NICO measures the absorption of 4 spectral lines and calculates the concentration of nitrate. The NICO is not suitable for saltwater.