Falmouth Field Course 2017

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Lab Protocols

Dissolved Oxygen

Dissolved oxygen was obtained utilising the Winkler Titration method (Grasshoff, et al., 1999). This included the addition of 1ml sulphuric acid our sample. The sample was then placed in an endpoint detector and mixed using a magnetic stirrer to dissolve the precipitate into a yellow solution. Sodium thiosulphate (normality 0.22) was then titrated with the sample using a dose tube until the endpoint was reached.

Phosphate

Phosphate concentrations were calculated using a Manual Dissolved Phosphate Procedure, see Parsons, et al. (1984). Each phosphate sample reading was obtained using a 100ml cylindrical cell and U-1800 Spectrophotometer with replicates taken every fifth sample.

Nitrate

Nitrate concentrations were calculated using the Nitrate Flow Injection Method (Johnson & Petty, 1983). Each sample was filtered to create 10 ml of filtered stock and then approximately 10 microns steadily injected into a network of fine tubing. The sample then entered a 1 cm spectrometer cell, where it outputted a voltage, converted into red and blue peaks by an analogue chart display. Each injection was allowed 3.8 minutes to travel through the tubing.

Silicate

Our silicate procedures can be understood in detail by looking at the methodology established by Parsons, et al. (1984). Briefly: we first calibrated the spectrophotometer using standards and blanks to quantify any uniform variation in the readings. 6ml of ammonium molybdate and 9ml of mixed reducing reagent was added to the collected samples, replicates and blanks which were left to stand for two hours. The samples were then run through the spectrophotometer at 810nm to measure the absorbance and develop a conversion graph for silicon concentration.

Figure 1: Nitrate work bench. (left to right) Filtered sample bottles, constant speed motor, point of injection, reagents (Sulphanilamide & NEDH), coiling and spectrometer. (05/07/17).

Figure 2: Analogue chart display

Chlorophyll

Our chlorophyll method follows that outlined by Parsons, et al. (1984). First a blank was recorded by taking a fluorimeter reading for pure acetone. Then our filtered water samples were distributed into test tubes and similarly tested. The actual chlorophyll concentration is calculated from the fluorimeter reading using the equation: (Volume of acetone/Volume of seawater) x Fluorometer Reading (Parsons, et al., 1984).

Figure 3: Phosphate samples

Figure 4: 100ml cell in the

U-1800 Spectrophoto meter

References

Grasshoff, K., Kremling, K., & Ehrhardt, M. (1999). Methods of seawater analysis. (3rd, Ed.) Wiley-VCH. Retrieved July 10, 2017

Johnson, K., & Petty, R. L. (1983). Detemination of nitrate and nitrite in seawater by flow injection analysis. Limnology and Oceanography, 28, 1260-1266. Retrieved July 10, 2017

Parsons, T. R., Maita, Y., & Lalli, C. (1984). A manual of chemistry and biological methods for seawater analysis. Permamon. Retrieved July 10, 2017