Environmental Science/Monitoring Water Quality
I am currently working on putting together a methodology for a monitoring programme of a brackish lagoon on the coast of Samos (a greek island close to Turkey). It is not a deep lagoon (about 1m at the most) the lagoon is cut off from the sea by a road though there is a small channel linking it to the sea- but we believe that not much if any sea water enters here. The site used to be home to a salt extraction factory, which may have contributed to the salinity of the ambient water.
My current problem is how to take water samples that are representative of the water body in terms of its salinity. Any advice you could give on this would be much appreciated. Questions:
- Can samples be taken from around the edge of lagoon or would they need to be taken in the middle to be representative?
- Would vertical profiles of salinity need to be taken i.e.will the lagoon be stratified or will there be a gradient of salinity from the top of the water column down. If so then a sample from the surface may not be representative.
- Could we use a thief type sampler to sample different depths of the water- if we are using waders (would wading mix the water column?)
Any help is very much appreciated! Feel free to give any advice even if it not a direct answer to one of the questions above. Thank you.
Volunteer at Archipelagos Marine Institute
It is not uncommon to have a profile of salinity differences across a body of water. So please plan on taking a couple of transits across the pond and taking samples at least at the midpoints, but even better if you can, depending upon the size of the lagoon, take 4-5 samples on each transit.
The water in the lagoon will likely be stratified. Omega instruments, for one, makes a good instrument which is not too expensive and will measure salinity in the range from 0.1 to 10%.
Yes, you will probably have vertical and horizontal salinity profiles, and unusual discontinuities in the vicinity of the outlet or inlet.
I would not recommend a thief. IF you are looking for gross analyses of concentration, then the thief is fine, but it will not allow you to develop a profile because when you transfer the contents to a flask for analyses, the profile will be lost.
Wading will mix the water column somewhat. I'd rather see you use a log platform or a platform created out of some 55 gallon drums and towed from one site to the other very slowly. Check with your professor or sponsoring agency to see if they will pay for the purchase of the Omega measurement device. It's less than 100 Eu. So it will be economical and as accurate as any device. Just remember to take distilled water with you on your float and decontaminate the instrument before each measurement profile. I would also have the measurements made in front of the floating platform because the pulling of the platform will disturb the profile.
Good luck and let me know if you need a hand plotting the information, as I have some suggestions there as well.