Metadata YSI Probe Current meter Chlorophyll

On the morning of 02/07/14 a time series survey was conducted of Fal estuarine water from the King Harry pontoon. Between 09:30 and 12:30, half-hourly measurements were recorded of the physical properties of the water using a current meter and YSI probe. Changes in temperature, salinity, dissolved oxygen and current speed were recorded over the time period along with chlorophyll which was measured from bottle samples taken at the same half-hour intervals. For more details see metadata.

The first measurement was taken half an hour after high water. The overall salinity was around 34 indicating strong seawater influence, however over the half-tide the salinity decreased by around 1 unit indicating increasing influence of river water towards low tide. As the tide ebbed, dissolved oxygen and chlorophyll concentrations increased significantly (8.5 to 9.5mgL--1 and 0.5 to 4µgL-1 respectively at the surface) as river water became more dominant and replenished the estuary. Velocity measurements showed little variation over the time series.

The temperature at all depths increased throughout the morning and the surface saw a change from 17.85 to 18.4°C. This is likely due to warming by the sun and decreasing depth allowing for greater heat transit through the water column.

Figure 1.0

Google Earth image of King Harry pontoon, sampled on 2/7/2014.

Metadata

Date:

Time:

Location:  

Weather:           

High Tide:

Low Tide:

2/07/14

0830 – 1130 UTC

50° 12'57N 005°1'39W

Sunny, calm weather with only 1/8 octaves cloud cover.

0909 UTC

1507 UTC

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YSI Probe

Overall the salinity range was small with the highest value being 34.75 at -5.5hrs and -4.5hrs and the lowest value being around 33.8 at high water (H.W). The data suggests that as the tide ebbs salinity decreases, likely due to the flushing of salt water out of the estuary.

Temperature decreases with depth due to denser, cold waters sitting below the less dense surface water. Surface water heating throughout the morning lead to an increase in surface temperature with time, from 17.85°C at H.W. to 18.40°C . Temperature at depth also increased with time, possibly due to heat advection from the warmer surface waters.

Figure 2.1

Salinity with depth (m) time series, recorded at 30 minute intervals.

Figure 2.2

Temperature (°C) with depth (m) time series, recorded at 30 minute intervals.

Figure 3.1

Water velocity (m/s) with depth (m) time series, recorded at 30 minute intervals.

The water velocities measured at the pontoon over half a tidal cycle presented no significant velocity changes other than at H.W. At this time, water velocity presented its highest values across the cycle at 0.95m/s and 1.55m/s at the surface and at 1m depth. However, this variation likely is not natural, as a close passing ferry at this time may have affected the water velocity of the area.  

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Chlorophyll

Figure 2.3

Oxygen concentration (mg/L) with depth (m) time series, recorded at 30 minute intervals.

Over the course of the tidal cycle there was an overall increase in the oxygen concentration away from high water, increasing to a maximum concentration of 9.69mg/l at -3hr, due to the increasing freshwater input which has a higher oxygen concentration.  There is a peak in concentration at 1m where primary production will be greatest. There is a general decrease in oxygen concentration with depth over the entire tidal cycle as there is less atmospheric interaction.

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Current meter

Figure 4.1

Chlorophyll Acetone derived samples taken at the surface of the water column at 30 minute intervals. The results displayed are averaged from the 2 samples taken simultaneously at the site.

Initial surface levels of chlorophyll was very low (<0.5µg/L), as the tide ebbed the concentration rose significantly (>4 µg/L). This is most likely due to an influx of algal material from further upstream.

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