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 Tamar Estuary

Introduction Biological Chemical Physical Time Series

Time Series…





The Saltash pontoon sits at site C15 in around 4m of water, measurements were taken between every 30 minutes and every hour during the day to produce a time series. Three procedures were followed- the first, lowering a probe into the water to measure temperature, salinity, O2 saturation, O2 concentration, pH and chlorophyll concentration. Water flow speed and direction were measured by lowering a flow fish into the water. Niskin samples were also taken to analyse in the lab.

 INTRODUCTION





The graphs from this time series data show several main area of interest. Sampling began at 08:30am (UTC). At this time, flow speed began to decrease causing salinity to increase in all water levels as high tide approached. Current speed dropped to a minimum at high tide (09:56 UTC) causing a salinity peak in all layers of water. After this peak, salinity decreases as the tide goes out and more fresh water flows past the pontoon. In addition to this, in the surface layer, the temperature peaked at 24°C- although this value may be a little high as the sun was warming the probe before it was placed into the water- as there was less movement of water to distribute the heat energy evenly through the water column.


After high water, the direction of the current changes and stays constant throughout the afternoon. The current speed increases in the surface layer up to a maximum of around 0.8ms-1. Increased current and nutrient flow causes an increase in oxygen saturation in the surface layer. O2 concentration remains lowers in the surface layer throughout the afternoon due to exchange with the air but increases overall due to stratification. Heat and nutrient stratification and increased light intensity cause production to increase which leads to more oxygen available in the water column.


Temperature in the top 1m of the water column peaks just after midday, accompanied by a drop in salinity in the surface waters. This suggests increased stratification as a warm, fresh layer of water sits on top of the main estuary water.  Current speed peaks at 1pm and then begins to fall as low tide approaches (15:50pm).


 FINDINGS

21. Pontoon time series data of flow speed against time (UTC) collected on 05/07/18.

22. Time series of salinity as sampled from the pontoon at Saltash on 05/07/18.

23. Time series of salinity as sampled from the pontoon at Saltash on 05/07/18.

24. Pontoon time series data of flow direction (°) against time (UTC) collected on 05/07/18.

25. Time series of O2 saturation as sampled from the pontoon at Saltash on 05/07/18.