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Data was collected every half hour from four stations set up along the pontoon, over the course of 2 hours, from 8.40 UTC to 10.40 UTC. The variables were measured at 1m intervals to a maximum depth of 5m so as to avoid fouling the instruments.

The Fluorimeter measures the intensity of the fluorescence emitted by the phytoplankton at the surface as well as at depth. Measurements were carried out at every meter up to a depth of 5m. The probe at the surface was used to assess the influence of cloud cover on the incoming irradiance at the surface of the water so that calibrations could be applied to the fluorescence depth measurements.

In the laboratory, a fluorimeter, zeroed using pure acetone, recorded the levels of chlorophyll within the samples collected from the pontoon. Each individual sample had to be inserted into the fluorimeter, which then measured the fluorescence. This process was repeated for all of the samples which provided an insight into how chlorophyll varied with depth for each station.

A flow meter was used to measure the flow velocity of the river’s estuary. Considerations for boat traffic had to be taken into account in order to provide flow measurements that were representative of the estuary’s natural discharge. The Enterprise Boats’ ferry moored at the pontoon at regular intervals, and at 10.45 interfered with the sampling as it had to be stopped whilst the ferry drew up to let passengers off.

A horizontal Niskin bottle was deployed at depths of up to 5m. The aim was sample the water column for chlorophyll. Water samples were taken at 1m intervals with an additional surface sample. Each water sample was filtered through a GFF filter before being preserved in acetone for future laboratory analysis.

The chlorophyll samples collected on the pontoon by the CTD were prepared back at the dry lab by the technicians. The samples fluorescence was then measured and recorded using a fluorometer. These values were then corrected by using the equation below.

In addition to the estuarine and offshore filters being analysed to determine the levels of chlorophyll present, a set of filters collected from the pontoon were also analysed, however these were used to construct a time series to be later compiled with the other variables measured. Due to time constraints and more regular samples being collected, only one filter per depth measured was collected, which increased the likelihood for errors. Filters were analysed systematically in the labs using a fluorimeter and the readings were converted (vol of ace 6ml/vol of sea water 50ml x reading) to give a μg/L result. If no chlorophyll was present then a negative result would be produced, however it is important to consider that if the filters had been damaged then this would also happen.

Methodology & Equipment

Flow Meter

Fluorimeter

Niskin Bottle

The Exo probe is used to measure sonde time (UST), temperature (°C), salinity (PSU), dissolved oxygen in both % and mg/l and pH. Measurements were taken every half an hour at a variety of depths. At the first station the Exo probe was deployed to 5m taking measurements every metre including the surface. Due to the tide going out the Exo probe could only be deployed to 5m to avoid it hitting the sediment in the estuary below when measurements were being taken after the initial readings. Due to a calibration error with the salinity reading on the Exo probe the readings taken had to be recalibrated. To get the correct salinity values 12PSU had to be subtracted from the values shown on the Exo probe.

Exoprobe