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Key Findings

A decrease in temperature with depth was observed. Over the period of study, an increase in temperature was observed due to reduced tidal input.

The water column was consistently more saline with increasing depth. Over the period of sampling, the surface layers of water gained a higher proportion of freshwater. Precipitation also had a perceptible effect on the salinity of the surface layer.

pH was variable over time and depth over a small range, becoming slightly more acidic over the sampling period.

Irradiance decreased with depth. During periods of cloud cover and precipitation, the radiant input to the surface layers was lesser than when the sky was clear.

The dissolved oxygen content of the water column decreased with depth. This remained consistent apart from during precipitation, when the dissolved oxygen content decreased.

Met data

Date: 25.06/.16

Time Range. 8:30 UTC - 12:00 UTC

Co-ordinates: : E181983.9m; N31650.546m

Air Temperature: 15oc

Cloud Cover: 5/8

High Tide: 09:14 BST

             21:30 BST

Low Tide: 03:24 BST

             15:41 BST

Introduction to Pontoon

Sampling was undertaken on a pontoon located downriver from the King Harry Ferry. Due to both marine and riverine influences, this was an ideal location to study mid-estuarine conditions across a semi-diurnal tidal cycle.

Equipment could be easily and safely deployed from the side of the pontoon, and its stationary nature allowed a time series to be created. This time series recorded the changes in the water column throughout the morning of the 25th, from 9.10am to 11.40am.

This data was used to create a time series, which could then be analysed to determine the relationship between riverine and marine influences and how they interacted at a fixed point in the mid-estuary.

Our aim was to create a time series using the data collected on the 25th June 2016 from the pontoon, with the purpose of determining the relationship between riverine and marine influences and how they interacted at a fixed point in the mid-estuary.

Various pieces of equipment were used to collect the data for the time series: A flow meter was used to determine flow speed (m/s) and flow direction (degrees from North); a multi-parameter Exo probe was used to sample pH, salinity, depth (m) and temperature (degrees Celsius); a light meter was used to determine light attenuation throughout the water column (% irradiance at surface) and finally a horizontal Niskin bottle was used to sample the water column. These water samples were then filtered using a GFF filter, before being stored in acetone for later laboratory analysis.

Aims and Objectives

It must be noted when looking at any findings and data presented on this topic that at the following times, other boats, Ferries using the river and heavy rain may have affected the results. The table below lists all other factors at the sample times.

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