Chemisty and Physical

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Chlorophyll (Fig 1 );-

Surface chl a filtered measurement

The exponential increase can be viewed as a result of heightened light levels occurring around 13:30 and 15:00 (UTC). Between 13:00 and 15:00 (UTC) where chlorophyll increases from 0.616 µg/L to 51.55 µg/L. As the tide ebbed there was a rise in the algal matter surround the pontoon from other regions of the estuary which can account for the growth.

pH (Fig 10);-

Values range from 8.16-8.29 with a general decreasing trend in pH with depth. Profile 13 shows an increase within the first 2m of the estuary before following the overall decreasing pattern. The unusual change in the surface waters can be a result of the increased evaporation as cloud cover reduces from 5/8th to 2/8th around this time.

Chlorophyll mg/L (Fig 7);-

A chlorophyll maximum is indicated in each profile at varying depths. Between 13:00-15:00 the maximum for each profile becomes increasingly more shallow with profile 10 measured at 4.04m (13.93mg/L) and profile 14 maximum measured at 2m (15.74mg/L). The chlorophyll maximum is dependent on the amount of light, nutrients and mixing within the water column.

Figure 5 - Briefing at the pontoon

Figure 6 - Surrounding environments from the pontoon

O2:

Oxygen readings were collected off the side of the pontoon every 30 minutes with the first profile was taken at 1200 UTC and the final profile taken at 1500 UTC. The YSI probe was deployed at the surface and descended at 1m intervals to the maximum depth. Indicated by the light probe (~5m), the maximum depth was calculated by taking 0.5m’s off the sea bed depth to ensure the probe didn’t reach the sea floor and become damaged.

Chl a:

At the same 30 minutes intervals (1200-1500 UTC), surface water was collected using a large plastic bottle. From this sample, 50ml was passed through a GF/F filter from which the filter paper was placed within small test tube containing 6ml of acetone. Samples were placed within a freezer overnight. The following day, samples were removed from the freezer and absorbance readings obtained using a fluorometer. Final values were then calculated after taking acetone and sea water volumes into consideration, using the following equation:

(Acetone value (6ml) / Seawater Volume (50ml)) X fluorometer reading.

Current (Methodology)

A current meter was deployed every thirty minutes off the King Harry Pontoon. The first profile was taken at 1200 UTC and the final profile at 1500 UTC. A surface reading was taken and another reading for every meter until the seabed was reached at approximately 5 meters.

Light (Methodology)

An irradiance probe was deployed every thirty minutes off the King Harry Pontoon. The first profile was taken at 1200 UTC and the final profile at 1500 UTC. A surface reading was taken along with a reading for every meter until the seabed was reached at approximately 5 meters. A ratio (Ez/Eo) was calculated with the irradiance values recorded.

In summary, a range of equipment was used to record and analyse data, collected from King Harry’s Pontoon. A number of trend and observations were made in reference to the estuary’s water column structure.

As the tide ebbs, chlorophyll becomes increasingly more concentrated due a reduction in volume of water. Increasing irradiance will induce vertical migration of primary producers, to maximise photosynthesis. Tidal movements and sun exposure both have a significant effect on water temperature within the estuary. Precipitation and physical movements, from boats and tidal regimes have an effect on the salinity structure within the water column. Surface water shows a reduction in salinity during periods of precipitation. Above 3m, water salinity is more susceptible to disruptions such as passing boat and the King Harry Chain Ferry. Surface waters of the estuary are supersaturated, oxygen is then depleted with depth as a result of biological activity. There is no significant change in pH within the water column profiles with time, however a slight neutralisation occurs with increasing depth. Anomalies, where water becomes more alkaline, can occur when the rate of evaporation increases. Changes in short term weather, e.g. cloud cover and sun exposure, effect irradiance within surface waters, altering water column ratios (Ez/Eo). At depth there is an increase in turbidity and resuspension of particles leading to a decrease in irradiance as less light is available to travel through the water column. Strong surface currents occur within the water column. The ebb tide has a significant effect on intermediate waters, increasing current strength that is subsequently reduced towards the sea bed. Sheer stress at the sea water-seabed interface produces a weak current at the sea bed.

Pontoon

A time series survey was conducted on the Falmouth estuary located at King Harry pontoon, on 26 of June 2015 afternoon. Physical and chemical measurements were obtained at the same time at every half an hour between 12:00 and 15:00 UTC to acquire data over a tidal cycle, totalising 7 tests. Current speed measurements were done with a current meter and light and dissolved oxygen were measured using an YSI probe. Water samples were taken with a plastic bottle and then filtered for later chlorophyll determination on the lab.

AIM – To measure water column characteristics over a tidal regime

YSI

Temperature (Fig 2);-

The general trend shows a decrease of temperature with depth. Profiles 12-14 show an increase in surface temperature to a maximum of 17.19°C, possibly a result of the increased sun exposure from 13:30 till 15:00(UTC). The large decrease between 2-4m, 16.23°C-15.17°C, at profile 14 may be a result the tidal movements in the water body.

Salinity (Fig 3);-

On average salinity is shown to increase with depth. Strong haloclines can be observed in profiles 13 and 14 between 2m and 3m. Profiles 8, 11 and 12 have a weaker halocline located around 1-2m. Values converge around 3m to a range of 0.2PSU where the water column is less susceptible to changing conditions such as passing boats or changing weather conditions that were experienced that day. Salinity values range from 33.83- 34.46 PSU, profile 8 (0.4m) and profile 12 (4.47m) respectfully. The rain which occurred between 12:00 and 13:30(UTC) would have reduced the surface salinity due to the increased freshwater input.

Oxygen % and mg/L (Fig 4);-

Oxygen saturation percentage typically decreases with depth. Values range from 118.1% at 14:00(UTC) to 144.2% at 15:00(UTC). Oxygen was also measured in mg/L using the YSI probe. Comparing figure? (O2 mg/L) and figure? (O2 %), profile 11 (13:30 UTC) has a smooth declining trend whereas in figure? (O2 %) there is a sharp decrease in saturation %. This suggests that there is an anomaly at 3m in profile 11. Oxygen within the upper areas of the water is reduced by biological activity, the values of oxygen saturation shows the water to be supersaturated at all profile times.

Figure 1 -A graph showing the change in chlorophyll over time.

Figure 2 -A graph showing the change in chlorophyll with depth from the YSI data

Irradiance µmol/m2/s (Fig 8);-

Irradiance levels decrease exponentially with depth for each profile. From 1200 to 1330 UTC there was 8/8 cloud coverage and at 13.30 it cleared up to 3/8. This weather change is reflected in the surface values for irradiance with value increasing from 0.36µm at profile 9 to 0.59 µm at profile 14.

Resuspension increases closer to the seafloor due to higher turbidity at the seafloor. This allows less light to travel through the water column decreasing irradiance.

Current m/s (Fig 9) ;-

In surface waters current strength is higher than that found with increasing depth. However all profiles except 9, show an increase in current around the mid-point within the water column. This can be seen as a result of the ebbing tidal movements occurring within the investigation time. The largest range is shown on profile 8 from 0.01 to 0.28m/s, this profile was taken closest to the changing in the tidal movements which can affect the current. The reduction in the current at the bottom of the water column is a result of the sheer stress between the non-moving sea floor and the fast moving water column.