In situ monitoring of eutrophication
Introduction
In situ monitoring is the observation and / or measurement of events in its original place (Latin: situs).[1]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 parameter into a signal which can be measured electrically.[2] The easiest way to measure environmental parameters is to take a water sample and analyze it in the laboratory. Disadvantages are that only a limited number of samples can be processed and information on temporal variations is limited. Sensors however gather data more quickly and record it accurately. These data are converted to a digital form and are processed at high speed. The data are subsequently retrieved and processed whenever and however the scientist wants. Alternatively, sensor technology can display graphs of data in "real time", the graph is constructed as the data is being collected, and the graph is then modified on the screen as the data is processed.
Oceanographic instruments
CTD
The CTD is the primary oceanographic instrument used to determine the conductivity, temperature and depth of the ocean. The CTD is made up of a set of small probes attached to a large metal rosette wheel. The rosette is lowered on a cable down to the seafloor, and scientists observe the water properties in real time via a conducting cable connecting the CTD to a computer on the ship. A remotely operated device allows the water bottles to be closed selectively as the instrument ascends. There can be a host of other accessories and instruments attached to the CTD package. These include for example Niskin bottles that collect water samples at different depths for measuring chemical properties, chlorophyll fluorescence(phytoplankton) and oxygen sensors that measure the dissolved oxygen content of the water.
