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Lab Protocol

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GEOPHYSICS

TAMAR SAMPLING

OFFSHORE

REFERENCE

Home Geophysics Tamar Sampling Offshore

Flying Pig and Porky Pig (RIB)

METHODOLOGY

Zooplankton:

samples were collected at Calstock, Above R. Tavy Confluence and Saltash (sites A, B and C respectively). They were collected using a 200 μm net fitted with a hydro-bioskiel flowmeter. The net was 0.5m in diameter and was trawled for 20 seconds at each site. The samples were fixed with 10% formaldehyde solution and stored in 1 litre bottles. The chemicals used were handled with care and gloves were worn when fixing samples in order to minimise contamination. 

Properties (Dissolved Oxygen, Surface Temperature and Salinity):

readings were taken at regular intervals of approximately 2 PSU. These readings were taken using a handheld probe.  Each property was recorded to 1d.p., alongside the time of reading, geographical location (latitude and longitude) and depth in meters. At sites A, B and C vertical profiles of temperature, salinity, dissolved oxygen and total-dissolved solids were taken. 

Chlorophyll:

3 replicated samples were collected. From the master sample (bucket sample) 50ml was filtered via a syringe, ensuring there were no leaks or breaks in the filter. The holder was then unscrewed and dismantled, exposing the filter. This was then, using forceps, folded and stored in a tube loaded with & ml of 90% Acetone. 

Phytoplankton:

We used random sampling over the course of the estuary. 4 samples were taken and stored in bottles containing Lugol’s iodine. Contamination was avoided by wearing gloves when handling the iodine and the water sample, care was also taken when using the Lugol’s to ensure none was spilled. 

Nutrients: Dissolved silicate and nitrate were filtered to remove both sediment and biota, avoiding contamination and alteration of the sample via biological processing. Nitrate samples were stored in plastic bottles and silicon in glass bottles.

INTRODUCTION

On Friday the 5th of July 2019 our group split across two RIBs, the Porky Pig and the Flying Pig, to go and take samples from the Tamar river above the Saltash bridge (Station C0).

It was decided to sample down the river in order to get the most complete set of salinities, reach all stations, and avoid becoming stranded by the ebbing tide.

The Porky Pig’s aim was to head up river to station A, collect samples of the lower Salinities (0 and up), and gather zooplankton samples. In order to gather samples close to 0 salinity, it was required to go above station A.

The Flying Pig was tasked with collecting samples from the upper end of the salinity range (up to 35).

AIM

The focus was to collect data to help create a complete data set of salinities from the Tamar Estuary with the Falcon Spirit and observe the behaviour of chemical and biological parameters with respect to the salinity.

UNEXPECTED OBSERVATIONS

On our way down the river travelling from station B0 to station C0, we observed a line of foam at the water surface. The line was potentially indicative of 2 water bodies mixing. The appearance of the foam line occurred at the meeting of the Tamar and the Tavy river leading us to believe that the line was indeed a result of water bodies mixing. We sampled the east (B1) and west (B2) of the line to investigate.

(Sound On)→

RESULTS

The resolution to the temperature salinity probe must be brought into account when considering the temperature-salinity depth profiles. The resolution of the probe was 0.1°C for temperature and 0.01 for salinity. Failure to consider the resolution may lead to recognition of features which are not present in the water column.

The water column measured at A-1 is fairly homogeneous (Fig.28). The temperature difference is 0.4°C and Salinity 0.01. These differences in temperature and salinity are not notable given the resolution. The water column is well mixed and there is no apparent intrusion of sea water at this station.

The water column measured at B0 shows slight stratification of the water column (Fig.29). The top of the water column is less dense with a temperature of 20.1°C and 27.50 salinity, the bottom of the water column is denser, with a temperature of 19.7°C and 28.60 salinity. This shows the layer of fresher less dense water over the denser sea water, and indicating that the water column is statically stable.

Having sampled a few metres east and west of the front between the rivers, samples were very closely matched.

temperature (<1°C), salinity (<1PSU), Oxygen saturation (0.1 difference), Chlorophyll (0.003 maximum difference), PO4 (0.05 difference), NO3 (0.6 difference), and silicon concentration (1.2 difference).

Temperature, salinity, Si, NO3, PO4, oxygen saturation, and chlorophyll are all very similar between the two samples.

The two rivers appear to be quite similar in composition. This could be genuine or perhaps the boat caused a degree of mixing resulting in the sample similarities.

It was an interesting aside to explore, however we were not equipped to take the extra samples to fully investigate the rivers meeting. To gain a better view of the two rivers and how the mix we would need to sample across a few transects across the width of the river at this point.