Tamar Estuary

Chemical Findings…

Method

Phosphate spectrophotometry:

Firstly the spectrophotometer was calibrated using mili-Q water, setting the standard to 0.

Start with the standards of known phosphate concentrations

For each sample a 1 cubed couvette was filled with the phosphate solutions, pouring the solution slowly to ensure no bubbles appear in the couvette

The couvette is then placed into the spectrophotometernsured

Take 3 readings from the machine for each sample

Record results in a table.

Repeat for each sample taken.

Findings

The graph shows how phosphate concentration changes with increasing salinity, from an endpoint at a salinity of 0 (upriver) to an endpoint seaward at a salinity of 35. By drawing a theoretical dilution line (TDL) between the end points, it can be seen that initially between a salinity of 0-7, there is a large removal of phosphate from the estuarine system, indicated by the data points falling well below the TDL. Past this there is no further large scale net addition or removal of phosphate as salinity increases to 35. This is indicated by the phosphate concentration (despite slight variation) remaining at around 0.5 micro moles per litre. Phosphate is a vital biological molecule for organisms who use it within ATP, cell membranes and within DNA. This could explain the rapid and sudden removal of phosphate shortly after the river water endmember, which is taken up into organisms whose growth is sparked by a change in salinity.

 PHOSPHATE

SILICATE

Method

First, add 5ml of each sample into separate tubes (x53 in this experiment).

Add 2ml of Ammonium Molybdate into each of the tubes and invert a few times.

Add 3ml of reagent and shake again.

Leave for a minimum of 1.5 hours to allow for the colour to develop.

Run a blank in a spectrophotometer to calibrate it.

Then run a series of standards to be able to draw a conversion curve.

Then put the samples one at a time in the spectrophotometer and read off the value.

Next, using the conversion curve, the readings from the spectrophotometer can be used to calculate a concentration value for each sample.

Findings

The graph shows how silicate concentrations changes with increasing salinity, from an endpoint at a salinity of 0 (upriver) to an endpoint seaward at a salinity of 35. By drawing a theoretical dilution line between the end points, it can be seen that initially there is a very rapid removal of silicate. Between 0-6 salinity, the silicate concentration is reduced by 22 micromoles per litre. This then remains constant at around 3 micromoles per litre at all of the sample points further downstream after 6 PSU suggesting no further net addition or removal of silicate. Silicate is vital from many marine organisms including diatoms who incorporate it into their cell wall as a grazing defence. The rapid removal in the graph upon changing salinities could be due to rapid diatom growth, causing an uptake in silicate from the estuary.

 SILICATE

SILICATE

Method

Water samples were collected and run through an auto-analyser to determine the nitrate and nitrite concentrations, these were then combined to give total nitrogen concentration.

Findings

The nitrogen concentration at the riverine endmember (5 PSU) for the Tamar estuary was 115 umol/L and was 0 umol/L at the seawater endmember (35 PSU), creating a declining TDL from the upper to the lower estuary.

The points in the mid estuary lie slightly below the TDL, but remain almost parallel, meaning the nitrogen remains fairly conservative but shows slight removal in the upper and mid estuary.

Towards the lower estuary, the points cluster

closer to the TDL, showing how there is less nitrogen removal towards the lower estuary.

 NITROGEN

SILICATE

Method

Add 1ml of 1M Sulphuric acid to the sample bottles (each around 120ml capacity).

The precipitate inside will start to dissolve and place the magnetic stirrer in.

Place in Dosimat 665 Machine and once all visible particulate precipitate has dissolved, place the tube from the thiosulfate container in.

Add sodium thiosulfate as necessary until the mixture goes clear and the Servoscribe 1.5 flat lines vertically.

Record the value of thiosulfate added.

Repeat for each sample and note results in table, next to bottle volumes and IDs.

Findings

For all the stations sampled in the lower estuary, via the Falcon spirit, the oxygen concentration was taken against depth (m), down to a maximum of around 27m (at station h11).

The surface O2 concentration was highest at station i18 with 249.2 umol/L and the lowest surface O2 concentration was at station g17 with 242.03 umol/L.

Stations c15, d13 and e16 show a fluctuating but overall almost vertical O2 concentration decrease with depth (m). Stations f12 and h11 show an even less fluctuating vertical decrease, and at these stations, the O2 concentrations down the water columns can be considered uniform.

Station j19, which is far downstream, shows an overall decrease in O2 concentration with depth, however there are three small peaks as it goes down, suggesting depths with areas of higher concentration than the surrounding waters.

Station g17 shows a short decrease in O2 concentration down from the surface, before taking a sharp increase at around 3m depth. Here, O2 concentration jumps from 240.5 umol/L to 246.6 umol/L, and once it reaches a maximum of 247 umol/L the increase slows to a plateau for the rest of the water column sampled.

 OXYGEN

Figure 5. Estuarine mixing diagram showing change in concentration of phosphate with respect to changes in salinity from samples collected along the Tamar estuary on 05/07/18 and processed on 06/07/18. A theoretical dilution line (TDL) has also been plotted using the riverine and seawater endmembers.

Figure. 6 Estuarine mixing diagram showing variations in phosphate concentration with salinity in the Tamar estuary with Theoretical Dilution Line. Plotted from samples collected on 05/07/18 and analysed on 06/07/18.

Above Figure 7. Estuarine mixing diagram showing variations in phosphate concentration with salinity in the Tamar estuary with Theoretical Dilution Line. Plotted from samples collected on 05/07/18 and analysed on 06/07/18.

Figure 8. Oxygen concentration plotted against depth for the lower Tamar Estuary from samples collected on RV Falcon Spirit on 05/07/18 and processed on 06/07/18.

Take 1L samples from each niskin bottle you wish to analyse for phosphate and silicate. Next you place a filter paper on a syringe and filter enough of original sample until the sample bottles are full with filtered seawater. Phosphate samples filter into a brown glass and silicate filter into a white plastic container. Throw away the filter paper and restart the process until enough samples have been gathered.

 BOAT WET LAB METHODS