Field Experiment#
Salinity in the Elbe estuary
Aim: To assess the variability of salinity in a semi-controlled coastal environment.
Learning outcomes: After the session, you will be able to describe salinity changes over a short time period (<1 day) as observed in a region of the German coast (e.g., Cuxhaven).
Background: Background: Now that you have examined salinity measurement in a controlled (laboratory) set- ting, you will now make measurements of salinity in the field. Here, you will assess the observed salinity changes and comment on the likely sources of variability including e.g. physical oceano- graphic, hydrologic and instrumental sources of salinity fluctuations.
Warning
Planning deadline: Please discuss and agree your planned experiment timing and practicalities (travel considerations) by the end of the day before the planned excursion. Planned equipment should be agreed by 15:00 so that there is time to pack.
Design an experiment#
Your likely region of study will be Cuxhaven, Germany, on the date specified in the course for the field experiment. You have access to the salinity instruments you’ve used so far during the laboratory exercises (with the exception of the salinometer). To plan the experiment, you should identify possible sources of salinity variability for the region, and make a hypothesis about what a time series of salinity would look like if taken from the side of the harbour in Cuxhaven.
The questions below are designed to help you outline your ideas.
Background on the region.
Do some background investigation into the region of Cuxhaven. Where is it located, and what might influence the salinity of the water there (physical processes)?
What are the possible timescales of variability associated with the processes identified in the previous section? I.e., over what time period of measurement would you expect each process to affect the measured salinity?
Come up with a couple sample hypotheses to design an experiment around.
What are your possible independent variables? Recall, your independent variable is the cause. Its value is independent of the other variables in your study (you can control it).
What is your dependent variable? The dependent variable is the effect. Its value depends on changes in the independent variable.
Choice of instrumentation
What are the pros and cons of the various instruments you have available to you to measure salinity? Consider both practicalities (size of the instrument, operating procedure) and the objectives of the experiment (required accuracy, suitable measurement ranges).
What instrument(s) will you need for the field experiment?
What auxiliary equipment (if any)?
For your chosen instrument, note any sampling restrictions (e.g., sample rate, requirement to be submerged, etc).
Outline the methodology
How will you set up the experiment, in broad terms. Where will you make measurements (geographic location), how often, what depth(s), for how long?
What other background information have you consulted and what did you learn? E.g. on tidal conditions, phases:
Or on riverine output?
Or other?
Revise and finalise
Design the results table/figure. Based on your planned experiment, what form will the results take? Is it a table of discrete values? Is it a graph or a time series plot?
Sketch an example of a results figure, graph or plot that will allow someone looking at the figure to say ’yes’ or ’no’ to the hypothesis. Is there any further information that could or should be determined from the figure?
Go back and check your hypothesis. Revise if necessary. Double check - is your hypoth- esis aligned with your planned ‘results figure’?
Check the instrument manual. Make notes for the instructions to include on how to set up the instrument for sampling, as well as how to make measurements and download data.
What role do you expect user error, instrumental error or other sources of error/noise to play in your measurements?
How else might your experiment turn out? I.e., what would a negative result look like? What about inconclusive? Any guesses as to why it might end up being inconclusive?
Go back and revise your experiment design. Revise if necessary. Based on travel time and your sampling requirements, when would you need to arrive in Cuxhaven? How often do you need to measure? What about other practicalities? Discuss and agree these with instructors by end of the working day before the excursion.
What other preparatory questions should be included here to aid you in planning an excursion? I.e., what have you considered that wasn’t included in this worksheet?