The data was taken on the King Harry’s Ferry Pontoon, located in the Falmouth Estuary close to a shellfish farm.The pontoon is used for a ferry and is open for leisurely use by the public, which at times would have affected some of our data.

Methods

YSI Multi-probe

The YSI Multi-probe was lowered close to the estuarine bed (the depth determined before each reading due to the fluctuation caused by the changing tidal height), measurements were taken at 1m intervals from the surface. The final reading was taken 0.5m from the estuarine bed whose depth varied by ~ 0.5m during the 3 hour period of data recording. The probe recorded; temperature (°C), salinity (PSU), pH, % dissolved O2, dissolved oxygen concentration (mgl-1), chlorophyll concentration (µgl-1) and turbidity (NTUs).  

Valeport Current Meter

The current meter recorded the speed (ms-1) and direction of flow of the water at 1m intervals from the surface.

Due to the pontoon being open to leisure craft for mooring and the premature arrival of the Conway flow measurements were taken occasionally from different points on the pontoon in an effort to reduce the impact of the boat presence on the current data.  

Chlorophyll

Two 50ml samples were taken from the surface water which were subsequently filtered using glass-microfiber filters. The filters were stored in acetone in preparation for laboratory analysis.   

Light Meter

Two sensors were deployed one remained on the pontoon the other was placed into the water taking readings of light intensity at 1m intervals from the surface. The sensor that remained on the pontoon recorded the ambient fluctuation in light in intensity due to influences such as cloud cover, these readings allow for the correction of the data obtained from the submerged probe.    

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Results

Temperature

Defined thermocline present between 1-2m depth that exhibits a general decrease in depth with increasing time. Shape of thermocline follows the salinity structure of the water column suggesting the presence of two distinct water species at the pontoon flowing over one another. Surface water heating throughout the morning lead to an increase in surface temperature with time increasing from 16.54°C to 16.65°C over the course of the three hour sample period. Temperature at depth also increased within this time possibly due to advection from the warmer surface waters.  

Minimum Temperature: 15.00 °C  -  Maximum Temperature: 16.83 °C  

Salinity

Contour plot reveals that lower salinities are located at the top of the water column (which coincide with higher temperatures) with an increase in salinity with depth. The contour shape of the halocline approximately follows that of the thermocline again providing support of two distinct water species. The estuarine salinity increases with the approaching high tide indicating the movement of seawater further up the estuary with the tidal movement (increase from 32.01 to 34.60 PSU).

Minimum Salinity: 32.01 PSU  -  Maximum Salinity: 34.60 PSU

pH

 Vertical gradient of pH with the highest values being located at the top of the water column and the lowest at the estuarine bed, depth of intermediate values reflects the boundaries of the halocline.

Minimum pH: 8.13 - Maximum pH: 8.23

Dissolved Oxygen- Figure 1.

In a similar fashion to pH dissolved oxygen is vertically separated with the highest values located at the top of the water column and the lowest at the estuarine bed this is due to the reduced atmospheric interaction at depth. Two distinct peaks occurred at ~1m depth, one at 09:30:00 and the other at 10:30:00.

Minimum Dissolved Oxygen: 113.3 % - Maximum Dissolved Oxygen: 134.7 %

Chlorophyll Concentration (YSI Multi Probe)

No clear vertical separation, two distinct peaks located at ~1m depth (08:30:00) and ~4m depth (10:30:00).  

Minimum Chlorophyll Concentration: 2.81 µg/L  - Maximum Chlorophyll Concentration: 25.92 µg/L

Chlorophyll Concentration (Surface Samples) - Figure 2.

No significant increase across the 3 hour sample period, however there is a fluctuation of ~ 0.1µg/L from each instance of measurement.

Minimum Chlorophyll Concentration: 0.002 µg/L - Maximum Chlorophyll Concentration: 0.122 µg/L

Current speed - Figure 3.

The highest values of flow are located at median depths between 2-4m with low values found at the top and bottom of the water column. The lowest values (< 0.02 ms-1) are located at the estuarine bed ~5m. There is a period at 11:00:00 where flow at median depth significantly declines and then resumes at 11:30:00, a phenomenon possibly linked to the influence of the tidal cycle (High tide at 11:05:00) which induced a period of slack water.

Minimum Current Speed: 0.000 ms-1  -  Maximum Current Speed: 0.164 ms-1

Light Intensity - Figure 4.

Exhibits a fairly uniform decrease with depth, two peaks were recorded in the surface water at 09:00:00 and 11:00:00.

Minimum Light Intensity: 0.54 %  -  Maximum Light Intensity: 45.26 %

Turbidity - Figure 5.

Between the times of 08:30:00 and 10:00:00 the greatest turbidity is located at the estuarine bed ~4.5-5m, the turbidity then abruptly decreases post 10:00:00. A second peak can be observed further up the water column (3m depth) at 11:00:00. In general there is little turbidity at the surface. Minimum Turbidity: 0.87 FNU  -  Maximum Turbidity: 1.98 FNU

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Discussion

The estuary salinity increases with time and approaching high tide (11:05), indicating the movement of seawater into the estuary. Lower salinity values at the surface shows a stratified estuary. Temperature and salinity present opposite behaviour, with higher temperatures in surface coinciding with lower salinity values. The shape of thermocline follows the salinity structure of the water column suggesting the presence of two distinct water species at the pontoon flowing over one another. Temperatures decreases with depth during the entire sample period.

The top of the water column presents the highest values of pH and dissolved oxygen due to atmospheric interaction, dissolving CO2 and O2. pH and dissolved oxygen decrease with depth as atmospheric interaction decreases. Two distinct peaks occurred at around 1m depth, one at 09:30 and the other at 10:30. This can be caused by wind and current changes.

Chlorophyll concentration do not show vertical separation, but present two distinct peaks around 1m depth (08:30) and around 4m depth (10:30).  This can be explained by current speed and direction.

Current speed presents higher values between 2 and 4 meters, with lower values at the bottom and at the surface. At around 11:00 the flow at median depth significantly declines and then resumes at 11:30, a phenomenon possibly linked to the influence of the tidal cycle (high tide at 11:05) which induced a period of slack water.

Light intensity decreases with depth, presenting two peaks in surface at 09:00 and 11:00.

Turbidity presents higher values in estuarine bottom from 08:30 to 10:00. Around the high tide period (11:05), a second peak stands out around 3 meters deep. This could be caused by a decrease in current speed (around high tide). At middle depths (from 1 to 3 meters), turbidity decreases with increasing time until 11:00, while current speed presents high values.

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Date: 25.06.2015

Time: 8:30 (UTC)

Location: King Harry’s Ferry Pontoon

                50° 12'57 N

                  005°1'39 W

High tide: 11:05   4.1m

Low tide: 17:35    1.8m

Cloud cover: 3/8

Sea state: 2/10

Disclaimer- The views shown here are solely of group 4 and do not necessarily reflect the views or opinions of the University of Southampton.

Falmouth 2015 Group

Figure 1. Dissolved Oxygen Contour Graph

Figure 2. Chlorophyll over time

Figure 3. Current speed contour graph

Figure 4. Light intensity contour graph

Figure 5. Turbidity Contour graph

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