Sampling of surface water and sediments Flashcards
At which depths would you sample a lake that is 20 m deep and why?
You should sample at 0.5 meters below the thermocline, and 1 meter above bottom to get a representative sample
What do you separate if you filter the water with 0.2 um filters?
To separate between dissolved and particulate phase. Colloids can be found in sizes that fit both phases.
What could happen with the fractions if you don’t have the possibility to filter your sample on site and instead ask the laboratory to filter the water?
A lot of things can change with the speciation of the sample if it comes into contact with oxygen. It takes some time for the change of speciation. If the lab filters then they might filter away all the particles that from the beginning were ions. If there is no filtration the lab could also dissolve the particulate phase which then could give wrongfully high concentrations of for example dangerous metals that are only in particulate phase in normal conditions.
How should you store water samples and sediment samples until they reach the laboratory for analysis and why?
For water samples it is important to know what you are looking for, if it’s metals you should never use a glass bottle since they contain silica and if you’re looking at organic matter you should never use a plastic bottle since they contain organic matter themselves. You should also store the sample dark and cold to avoid chemical reactions in the sample.
Avoid putting the samples into contact with oxygen.
Name a situation/”identification of an environmental problem” when it is good to use a Ruttner sampler?
A Ruttner is good to use when you want to take samples from a certain depth in still water, could be from a lake. If you’re looking for eutrophication it is useful to take samples from different depths and places in the lake.
What is the difference between looking at the results from water samples and water moss samples?
Water moss will take up metals that are in the water and if you analyze them you can see over a longer period of time which metals have been there. Water samples show the metals in that exact moment you sampled.
If you want to trace climate changes by analyzing the sediments – Which sediment sampler would you use?
You would want to take a core sample, these give a lot of information when you see for example varved sediments and bioturbation.
Explain how the lead (Pb) concentration in sediments can be used to trace periods of Economic Development several 100 years ago.
Peaks in lead concentration are traced to economic development and extensive metal production whilst the declines show of diseases affecting the population and economic crises.
A new harbor should be established and sediments needs to be dredged in order for the ships/boats to reach the harbor. Your task is to determine if there are any pollutants that could be spread during the dredging. Which sampling equipment would you use and why?
I would use one of the corers (gravity corer, kajak corer, Russian peat corer) and take samples of the sediments over a grid of locations. This would show different metals that can be in the sediments. The sediments are mostly in an oxygen-free location and when dredging will be done these can be dissolved into the water due to new oxygen. Just taking a sample of the surface sediments won’t give an accurate picture.
What is the difference between a direct and an indirect flow/discharge measurement method?
The direct methods involve going to the stream and using some king of equipment there to measure the flow. The indirect methods on the other hand requires no equipment at the stream because you use mathematical methods or data available online.
Explain how a measurement using a rod suspended current meter is to be done.
A rod suspended current meter is a propeller that you put down in the water and it then measures the flow. You need to divide the water into sections (preferably more than 30 sections) and then measure the flow close to the surface and close to the bottom in each section, this is due to the flow being stronger closer to the surface. You will get an estimation of the mean current.
How does the water flow affect the metal concentration in a river?
The dissolved phase will be diluted during the spring flood and the concentrations will be lower.
Sometimes the spring flood can bring high concentrations of metals that have diluted during the winter (Fe3+ in sulphide ground)
