Marine Biology (2+1)

THE NANSEN REVERSING WATER SAMPLER

Like the Freidinger’s water sampler, it is also employed for taking water samples for phytoplankton enumeration from subsurface levels, but its operation varies slightly from that of the former. The reversing bottle is made of brass and plated inside with tin or silver or coated with a special lacquer. It is fitted with a drain cock and an air-vent to facilitate draining the trapped water sample. The reversing water samplers are available in different capacities (750-1250 ml). Each sampler is also provided with two plug valves, one on each end of the metal cylinder and are operated synchronously by means of a connecting rod fastened to the clamp which secures the sampler to the wire rope. When the sampler is lowered, the clamp at the lower end and the plug valves are in open condition, so that, water can pass through the sampler. The sampler is held in this position by the release mechanism which passes around the wire rope. But, when, the messenger is dropped down the rope, it strikes the release and the sampler immediately falls over and turns through 180^o, shutting the valves which are then held closed by a locking device. The water sample of the desired depth so trapped in the bottle can then be pulled up onto the vessel in a closed condition. For collection water samples from different depths simultaneously, a series of water samplers are suspended one above the other from a wire rope and re lowered into the depths in the open state. In this case, after reversing one bottle, the messenger releases another messenger that was attached to the wire clamp before lowering. The second messenger closes the next lower sampler releasing a third messenger and so on.

The water collected through the different water samplers is either centrifuged or passed through fine mesh nylon or filter papers to separate the plankton present in it. Alternately, the water may be subjected to enumeration by filling in Utermohl’s tubular chambers for sedimentation and further quantification.