Southampton University Falmouth 2015

Group 13

© B Carter

Disclaimer: The views and opinions expressed are those of the individual and not necessarily those of the University of Southampton or the National Oceanography Centre, Southampton.

Figure 101 - pH down water column

Figure 100 - Salinity down water column

Figure 99 - Temperature (°C) down water column

Figure 98- Turbidity (FTU) down water column

Figure 97 - Current speed (m/s) down water column

Figure 96- % O2 saturation down water column

Surface water rich in O2, throughout the day with maximum concentration of 150-160 in top 2metres at low tide. From 12:00:00 until 14:00:00 there is a notable decrease in % O2 saturation with a lower maximum concentration of 150 in the upper 1 meter of water column, at high tide. The O2 % saturation decreases gradually down the water column. There is upwelling of low oxygenated water at high tide. As the tide becomes lower the % O2 saturation begins to increase again.

The current speed is high at low tide. The fastest currents are visible towards the river floor. The current is slowest at high tide and fastest at low tide. Max flow velocity of 0.20m/s at approx 10:00:00 GMT and 14.30 GMT and min velocity of -0.05, -0.10 at 12:30:00 GMT. Velocities at each time tend to be homogeneous down the water column. Surface waters, in the upper metre are slowest.

At this position the water in the estuary is not turbid and this is shown throughout the day. Down the water column there is little to no variation in turbidity.The water is most turbid (2-3 FTU) at low tide at depth 2-4 meters, this could be explained by the period of stand still of water at high tide which allowed sediments to upwell. Low turbidity at high tide of 0-2 FTU. As the tide rises the area around the estuary floor is more turbid than the water column both at low tide and on approach to low tide.

Highest temperatures were reached in the surface waters (upper meter) and this can be seen throughout the course of the day because of incident shortwave radiation from sunlight. Gradual upwelling of cold water at high tide with the maximum upwelling seen at 13:00:00 GMT. Around 09:00:00 GMT, at low tide, sun can penetrate further reaching almost the the floor and most of the water column is warmed. Thermocline is deepest directly before and after high tide. More defined thermocline at and after high tide than at low tide. Highest temp 18.0C to lowest temperature 15.0°C

Alkalinity of the water generally decreases with depth. At the surface, removal of carboxylic acid with phytoplankton respiration causes an increase in pH. Removal decreases with depth because there greater attenuation of light with depth and hence decreased rates of photosynthesis.

At 13:00GMT there appears to be upwelling of water of lesser alkalinity with the large volume of seawater forcing it towards the surface at high tide.

Salinity is generally lower at surface than at depth, possibly due to saline tidal water entering the estuary under a small but non-negligible freshwater input. There is a gradual increase in salinity with time towards high tide as seawater enters the estuary.

Max salinity = 36, min salinity = 29

Pontoon Results

On each of the contour graphs the maximum depth throughout the day is represented by a black line. Therefore it is possible to see that high water was reached around 13:17:00 before the tide began to retreat. Before high water it was expected that there would be a higher salinity as the sea water floods the estuary. Beyond high tide there would be a noticeable change, particularly in salinity between the flood and ebb tides.