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Falmouth 2017 - Group 12 7TITLE

Estuary

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Station 26 (temp, salinity depth profile)

The temperature of the water decreases with depth the surface layer has been heated by light exposure and convection takes the heat downwards. The colder water is also denser than the warmer water above which creates a thermocline.
The salinity of water decreases with depth due to saline water being denser than fresh water.

There appears to be a shallow water thermocline at 4m depth which drops from about 16.5 deg C to 15.7 deg C between 2m and 6m.
The surface temperature is about 16.5 deg and the surface salinity is about 33.7 PSU.
The maximum salinity at depth recorded was 34.2 PSU.
The minimum temperature recorded at depth was 14.5 deg meaning there was an overall quite sharp decrease of 2 deg C in 16m.

Station 27 (temp, salinity depth profile)

Temp decreases with depth sharply from about 3m to 17m.
Salinity increases with depth up to ~18m before remaining fairly stable.
There is a thermocline at 17 m.

Station 28 (temp, salinity depth profile)

 Temp decreases with depth sharply until around 17m at which point the temperature remains constant.

 Surface salinity drops considerably then increases again after a few meters this could be due to a fresh water input in the estuary. Salinity reaches a maximum at about 20m depth before slightly decreasing for the next 10m, which is unusual as it is expected that the denser saline water would sink below the freshwater inputs from inland.

 This is quite a complicated profile and may point to a salt wedge at depth.

 Thermocline at around 17 m.

Station 29 (temp, salinity depth profile)

Temperature decreases with depth.
Strong thermocline at 11 m. At 11m there is a major drop in salinity from 34.16 to 34.07.
The salinity decreases with depth however the change is so minimal as the water is already highly saline so shouldn’t indicate a salt wedge.

Station 26:

Chlorophyll increases slightly with depth, there’s a small change of around 0.4µg/L. After this slight increase, Chlorophyll decreases again with depth which follows the decrease in Phosphate (PO4) concentration. As chlorophyll increases in the surface layer, Nitrate (NO3) decreases, possibly being used up by phytoplankton.

Station 27

NO3 and PO4 show similar behaviour, except that the change in NO3 is very large compared to the change in PO4. Chlorophyll follows the same pattern in the surface layer and appears to stay the same to a depth of 30m however this would lead one to question these results.

Station 28

At this station NO3 and PO4 show an inverse relationship, with NO3 increasing within the surface layer and PO4 decreasing. Chlorophyll shows a slight increase in the surface, but decreases rapidly to a very low concentration at depth. NO3 and PO4 remain at constant concentrations between 5m and 28m, this could be due to the estuary constantly changing states with the movement of the tide, and it would seem there is a large influence of this tidal movement on the surface layer, with the deeper water being less affected.

Station 29

Around 10m, both PO4 and NO3 increase very rapidly. One would assume chlorophyll to follow with the availability of nutrients, but an increase is visible in chlorophyll with depth which could mean there is a slight delay in the chlorophyll growth after the input of nutrients from fresh river water.

Describing physical data – Estuary

Describing chemical data – Estuary

Physical

Chemical

Phosphate, Nitrate v.s Chlorophyll

Temperature and salinity v.s. depth:

The estuarine mixing diagram for Phosphate from the data collected on 7/7/17 shows non-conservative behaviour, as the data points for phosphate concentration do not fall directly on the Theoretical Dilution Line (TDL). The data largely falls above the TDL, showing that an addition process is in place in the Fal Estuary. This could potentially be due to sewage and agricultural run-off into the estuary, especially since the Newham Sewage Treatment plant is very nearby in Truro. There is an obvious anomaly at salinity 35.17 PSU, concentration 2.99 µmol/L. The data also appears very concentrated at the higher salinities, this is due to a lab error meaning our data collected from Winnie the Pooh cannot be presented – therefore the midrange salinities are not present on the plot.

The estuarine mixing diagram for nitrate from the data collected on 7/7/17 shows non-conservative behaviour, as the data points for nitrate concentration do not fall directly on the Theoretical Dilution Line (TDL). The data largely falls below the TDL, showing that a removal process is in place in the Fal Estuary. This could potentially be due to uptake by phytoplankton and zooplankton in the estuary as a nutrient for growth; this is particularly likely due to the strong sunlight in the preceding week, meaning that phytoplankton photosynthesis was not limited by sunlight.

The estuarine mixing diagram for silicate from the data collected on 7/7/17 shows non-conservative behaviour, as the data points for silicate concentration do not fall directly on the Theoretical Dilution Line (TDL). The data largely falls below the TDL, showing that a removal process is in place in the Fal Estuary. This could potentially be due to uptake by phytoplankton and zooplankton in the estuary as a nutrient for growth; this is particularly likely due to diatoms taking up silicon for their tests. Furthermore, the strong sunlight in the preceding week meant that phytoplankton photosynthesis was not limited by sunlight.

Phosphate, Nitrate and silicon Mixing Diagrams

Phosphate:

Nitrate:

Silicon:

Biological

Describing biological data – Estuary

Description and Analysis of Contour plots of Salinity, Temperature, Chlorophyll, Oxygen, pH, Turbidity and Light attenuation on the Pontoon 07/07/17

Salinity

Salinity down the estuary at the pontoon was consistently high at ~33.8 psu between 8:30 and 9:30 UTC. At 9:30-10:00 the entire estuary becomes less saline as from 9:00 only 3m were measured due to the estuary depth and therefore we can disregard the 3-4m area. At 10:30 UTC the top meter of the estuary falls to 32.6 PSU at around 11:00 UTC up to 2m has fallen to 32.6 PSU while the top 0.5 meters has dropped even lower to 32.2 PSU. The fall in salinity falls in line with an ebb tide as there was saline water taken away with the freshwater input remaining the same, increasing the ratio of freshwater. The less saline water at the surface at 10:30 is due to the fact that river water will warm up faster in the summer than seawater due to volume and therefore is less dense in two ways. As the tide ebbs further this less saline water will be able to reach deeper into the estuary, as is seen at 11:30.

Temperature

The temperature of the water for all depths at 8:30 UTC was ~17 deg C and remained the same until about 9:30 when the first 2 meters started warming. At 10:00 the top meter was 17.5 deg C and 2-3.5m started to warm. At 10:30 UTC the top 0.5 meters began to warm considerably to about 18.5 deg C and the heat moves down to 1m by 11:30 UTC due to heat convection. The temperature also follows a similar pattern to the salinity plot, giving further evidence for the idea that the ebb tide brings in warmer freshwater which is less dense on top of the ebbing saline water below. This is why, as well as direct light radiation, the surface will heat much quicker and the lower depths will heat as the estuary depth lowers allowing the less saline water to sink and heat convection to take place.

Chlorophyll concentration

Chlorophyll concentration below 2m at 8:30 is about 2 ug/L and above is slightly lower at 1.5 ug/L. The concentration maximums occurred at 2 meters at 10:00 and 11:00 UTC. The maximum concentration was 3.0 ug/L. From 10:00 the contour plot shows a large purple area of 0 ug/L at the estuary bed, this is because the estuary depth reduced and readings were only taken for 3m and above. From 10:00 UTC onwards the surface chlorophyll is much lower than the rest of the estuary at 0.5 ug/L. The chlorophyll concentration is dependent on light and nutrients, as the day goes on the light becomes more intense and permeates further into the estuary.

Oxygen Concentration/ Oxygen Saturation

The oxygen concentration below ~3.75m remained at 9.7mg/L or below throughout the time series. At 8:30 UTC the entire depth profile was ~9.7mg/L O2. At 9:00 the oxygen concentration of the entire water column increased until around 10:30 to ~10mg/L. The water above 1m depth then decreased back to 9.7mg/L from 10:30 to 11:30. Between 1.5 and 3m depth the concentration continued to increase achieving a maximum concentration at 2m of 10.2mg/L with our last reading at 11:30 UTC. At 10:30 the decrease in oxygen saturation above 1.5m depth suggests that respiration is happening at a faster rate than photosynthesis. Between 1.5-3m photosynthesis continues to produce oxygen with the largest rates at 2m depth and a maximum of 130% at 11:30 UTC.

Turbidity

At 8:30 UTC the turbidity of the estuary down to a depth of 3m is 0.8 NTU. From 3-4m the NTU increases from 0.8-1.8 drastically. At 9:00 UTC below 1m depth becomes slightly more turbid, up to 1.2 NTU. At 10:30-11:00 the water surface becomes a lot more turbid increasing up to 1.4 NTU before reverting back half an hour later this is possible due to ferry activity coming in to the pontoon and disturbing the river bed at this time (the enterprise 3). At 10:30 the water below 3.5m depth’s turbidity seems to rapidly fall however this is actually due to the water depth being less than 3.5 at that point and therefore there was no data.

Light attenuation

The graph shows what is expected from a contour plot showing light attenuation in the surface layers of water (between 0 and 0.5 m) there is a high light attenuation, this is due to the water having a low turbidity. However, as the depth increases, the light attenuation also decreases this is because light is being absorbed by the water. The light attenuation decreases in the surface waters at around 10:30 UTC this could be due an increase in turbidity because of the nearby ferry (The enterprise 3). The deepest light attenuation is at 11:30 UTC and this would be because the sun was directly overhead and therefore the angle of contact would be greatly reduced.

Salinity

Temperature

Chlorophyll

Oxygen

Turbidity

Light

Zooplankton Estuary abundance:

Phytoplankton Estuary abundance:

Station 26

Station 26 is dominated by Mesodinium rubrum with 49% of abundance. The species richness is 7 and the species evenness is 0.788.

Station 27

Station 27 is dominated by Mesodinium rubrum with 40% of abundance. The species richness is 5 and the species evenness is 0.893.

Station 29

Station 29 is dominated by Chaetoceros spp with 40% of abundance. Followed by Rhizosolenia spp with 27% of abundance. The species richness is 10 and the species evenness is 0.766. the total phytoplankton count is 98 specimens per millilitre.