University of Southampton OES Undergraduate Falmouth Field Course 2016 - Group 3 databank and initial findings.
Disclaimer: The views and opinions expressed are solely those of the contributors, they do not reflect the views and opinions of the University of Southampton.
Estuary sampling - R.V. Bill Conway
On the 23rd of June 2016, a study was undertaken on the RV Bill Conway in the Fal Estuary to investigate and understand how the water column changes, over depth and time, along the estuary. Profiles were obtained at 6 sites along the estuary, from near to the river end member (50°14.391N 005°00.878W) to the mouth of the estuary, near Black Rock (50°09.030N 005°01.804W). Starting at 07:00UTC the tide was beginning to go out. The data collected from the stations will show how the estuary changes spatially as the tide is going out.
CTD, Secchi Disc and Zooplankton sampling
Deck hands were responsible for deploying the OSI CTD at each station. The CTD was attached to a rosette along with six operating Niskin bottles, a fluorometer, and a transmissometer. The Niskin bottles were carefully prepared before each deployment to ensure that they would fire correctly. Two bottles were fired at each depth. Other group members were responsible for transferring the samples to smaller containers in order to use later.
Following the CTD deployment a secchi disc was deployed from the starboard side and a measurement was taken and recorded for each station.
The deck hands were also responsible for deploying the zooplankton net which had a diameter of 50cm and had 200 micron mesh. It was deployed three times, for five minutes each, off the port stern. The net was rinsed and the sample collected and transferred into a smaller sample bottle.
Biological and Chemical analysis
A temperature and salinity profile was obtained as the CTD was
lowered through the water column providing an idea of water column
structure. From which, we were able to choose the depths to sample
dissolved oxygen.
Water samples were collected in Niskin bottles at surface, mid and
deep depths relative to the seafloor of the station. The water
samples collected were treated as follows:
Dissolved oxygen:
- Rinse glass bottle with water from depth sampled
- Put tube connected to Niskin bottle output to bottom of bottle and fill glass bottle right to top, minimising the exposure of the water sample to the atmospheric oxygen
- Pipette 1ml of manganous chloride into the sample. This precipitates out the oxygen present in the water sample, preserving it.
- Then pipette 1ml of alkaline iodine into the sample. This neutralises the reagents in the solution and prevents further change.
- Carefully place the lid in the glass bottle. Do this slowly so air bubble are not added to the sample.
- Store in a bucket containing sea water deep enough to cover the bottle.
Silicon:
- Rinse syringe and plastic bottle with sample.
- Use the syringe to fill plastic bottle with water sample.
- Make a note of the bottle number for each site and depth.
Nitrate and Phosphate:
- Rinse syringe and glass bottle with sample.
- Use syringe to fill glass bottle with water sample.
- Make a note of the bottle number for each site and sample.
Phytoplankton:
- Rinse the measuring cylinder.
- Add 100ml of water sample to glass bottle containing Lugols solution.
Chlorophyll:
- Filter 50ml of seawater through filter paper
- Remove filter paper using tweezers and add to a tube containing acetone.
To determine our nutrient, chlorophyll, and dissolved oxygen concentrations we used various methods including Parsons, Maita, and Lalli (1984) for the chlorophyll, dissolved phosphate and silicon concentrations. We used Grasshof, Kremling, and Ehrhardt (1999) for dissolved oxygen concentration and Johnson and Petty (1983) for the Nitrate by Flow injection analysis method.
Spectrophotometry was used to measure phosphate and silicate levels in estuary samples as well as in reference samples of known concentrations (as described in Parsons, Maita & Lalli, 1984, which in turn is based on Murphy & Riley, 1962). This method is useful for measuring low PO4 concentrations.
Differences:
- Beam in original method operates ta 885nm, in our experiment this was attenuated to 882nm.
- For very low levels, a blue colour is produced by extraction with iso-butanol and measured at 690nm, increasing sensitivity 5-fold (Stephens, 1963).
Initial processing of data can be found here:
Methodology
Environment Parameters (23/06/16)
Cloud Cover - 3-4 octants
Air Temperature - 19°C
Wind Speed - 6.03 knots
Wind Direction - N
Precipitation - None
Sea State - 2
Tide Times - H: 06:56, 19:08 UTC
L: 01:04, 13:21 UTC