In situ monitoring of eutrophication
Contents
Introduction
In situ monitoring is the observation and / or measurement of events in its original place (Latin: situs). Oceanographic instruments containing different types of sensors are used to monitor eutrophication in coastal waters. Sensors detect and respond to electrical or optical signals and convert the physical, chemical or biological parameter into a signal which can be measured electrically.
Oceanographic instruments
CTD
The CTD[1][2] - Conductivity (salinity), Temperature and Depth (pressure) recorder - is the standard oceanographic tool for continuously measurement of physical properties of sea water. The CTD is mostly attached to a frame with water-collecting Niskin bottles (CTD rosette). From the deck the rosette is lowered on a cable down to the seafloor and once in the water data are transferred via a conducting cable connecting the CTD to a computer on a ship. The Niskin bottles are closed at predefined depths to target water samples for further analysis. Other sensors to measure chemical or biological parameters such as dissolved oxygen, chlorophyll fluorescence (phytoplankton concentrations) and water light transmission can be added to the cluster.
Sensors
In this section we focus only on the sensors that measure parameters that need to be monitored in the frame of the OSPAR Eutrophication Monitoring Programme: [3]
Temperature
The simplest mechanical way to measure temperature is by using a mercury-in-glass thermometer. They are commonly used to measure sea surface temperature by placing it in a bucket of sea water. Electrical temperature sensors such as the Resistance Temperature Detectors (RTDs) and the thermistors are more frequently used on a CTD. A thermistor is a type of resistor composed of a small piece of electrically semiconductor material such as a resistor which exhibits a large change in resistance proportional to a small change in temperature (sensitive). Thermistors usually have negative temperature coefficients which means the resistance of the thermistor decreases as the temperature increases. The thermistor relies upon measuring electrical resistance which is directly or indirectly or inversely proportional to temperature. Thermistors are inexpensive, easily-obtainable temperature sensors. They are easy to use and adaptable. RTDs are sensors used to measure temperature by correlating the resistance of the RTD element with temperature. Most RTD elements consist of a length of fine coiled wire wrapped around a ceramic or glass core. The element is usually quite fragile, so it is often placed inside a sheathed probe to protect it. The RTD element is made from a pure material, typically platinum, nickel or copper. The material has a predictable change in resistance as the temperature changes; it is this predictable change that is used to determine temperature.
Salinity
- Phytoplankton chlorophyll-a
- Phytoplankton indicator species
- O2-concentration
- Macrophytes
- Benthic communities
- Nutrients
See also
References
- ↑ http://www.whoi.edu/instruments/viewInstrument.do?id=1003[1]
- ↑ http://noc.ac.uk/research-at-sea/nmfss/nmep/ctd[2]
- ↑ OSPAR Commission (2005), Agreement on the Eutrophication Monitoring Programme (Reference Number: 2005-4)[3]
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