Falmouth Field Course 2007
Group 4 - 'The Deep Sea Karma Junkies'
 


Martyn Papworth    Kris Stevenson    Sarah Chaplin    Elly White    Rob O'Brien    Beth Sharp

Alex Hazeldean    Dafydd Gwyn Evans    Harriet Harden-Davies    Katie Gowers    Joana Franca-Gomes


IntroductionBoats and EquipmentLaboratory Analysis MethodsOffshoreEstuarineGeophysicsConclusionReferences

1. Introduction


Figure 1.1 The Fal Estuary Basin


T
he Fal Estuary is situated in Falmouth, Cornwall along the Southwest Coast of the British Isles. The Estuary is defined by type as a Ria, a drowned river valley developed in high relief areas. It is supplied by 6 main tributaries and 28 smaller creeks. The main body of water within the estuary is known as Carrick Roads and is the deepest section of the estuary, with water depth decreasing landward. Due to relatively low river inputs the sediment is deposited in the rivers and the estuary is salt water dominated. The regional basin of the Fal Estuary can be seen in figure 1.1.

The Fal is macrotidal at the lower parts of the estuary around Falmouth with a maximum Spring tidal range of 5.3m, but becomes mesotidal in the more upper regions near Truro. It is the 3rd largest natural harbour in the world, and has recently been granted status as an SAC- Special Area of Conservation, due to the extensive Maerl beds and fisheries present within the estuary.

Large amounts of mining discharge in the past have led to the Fal being heavily polluted, especially during the Wheal Jane incident in January 1992 where large amounts of highly acidic metal laden water was released into the estuary. Evidence of this pollution is still seen in the sub surface sediments of the estuary, especially around Restronguet Creek.

During our time in Falmouth, our main aim was to measure the biological, chemical, physical and geophysical parameters within the Fal estuarine system and the immediate offshore area. Therefore allowing us to integrate, compare and contrast the data gained from all the research surveys undertaken to discover how the four main parameters change throughout the estuary.

 

 

 


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2. Boats and Equipment

RV Callista

 

RV Bill Conway

The RV Callista is primarily used for offshore research. Having a large Stern      deck with 3 deployment points and dry and wet labs on the vessel allows instantaneous data interpretation.

The RV Bill Conway is better suited for river and estuarine surveying, having an ‘A’ frame and side winches for various equipment deployment  

Specification:

Length - 19.75m
Breadth -
7.40m
Draft - 1.80m
Depth Midship - 2.85m

Deck:

'
A’ frame - 4 tonne capacity
Capstan - 1.5 tonne pull
2x side Davits - 100kg each
 

Specification:

Length - 11.74m
Beam - 7.40m
Draft - 1.30m
Cruising Speed - 9knots

Deck:

‘A’ frame - 750kg max
Capstan - 0.25 tonne pull
Side Davits - 50kg each
 

 

MV Grey Bear

 

Ocean Adventure RIB

The MV Grey Bear is used for offshore Geophysics studies using Side scan sonar and Grabs to obtain bathymetric data.
 

 

Ocean Adventure RIB is a fast and versatile Boat with a low Draft, therefore allowing it to reach into the upper most regions of the estuary to take samples where the other vessels cannot.

 

Specification:

Length - 15.00m
Width - 6m
Main deck - 10x6m
Well Deck - 10x2.75m

Equipment:

Winches - 3 in total
Grab - Van Veen Grabs
Bathymetric surveying - Side scan Sonar

 

Specification:

Length - 7.00m
Beam - 2.55m
Draft - 0.5m
Max Speed - 35 knots

Cruising Speed - 25 knots
Max Endurance- 1 day at sea
Range - 100nm

 
 


CTD & Rosette:

The CTD measures; conductivity as a proxy for Salinity, temperature and depth simultaneously. It is usually mounted on a rosette allowing other equipment like the Fluorometer and Niskin bottles to be mounted on it as well (figure 2.1). The CTD is very useful in providing vertical water column data and identifying important areas to take samples.
 

Niskin Bottles:
These are used to collect water samples from within the water column at pre-determined depths. They are triggered to close by a messenger either via shot sent down a line or via electronic messenger. On board the R.V Callista they are mounted upon the Rosette, with up to six bottles being used. The samples collected can be used for chemical and biological analysis.

 

 


Figure 2.1. A CTD & Rosette

 

Acoustic Doppler Current Profiler:
The ADCP uses sonar to calculate the current velocities present in the water column. It works by transducers sending out sound pulses on mono-frequencies in known directions. When the sound pulses are returned due to scattering in the water column or the sea bed they are shifted in frequency due to the Doppler effect, this causes the different elements to return the signals at different times. Over a determined time period and area, a current profile can be obtained giving information on the current velocities. The ADCP also gives information on backscatter, showing possible zooplankton numbers or the waves causing turbidity.
 

Secchi Disk:
The Secchi disk is a simplistic device used for measuring water  transparency. The disk is usually split into quarters painted in alternate black and white squares (figure 2.2). The usual diameter is 20-30cm, which is does not affect usability and is still large enough to be seen at depth. The disk is connected usually via rope and is lowered until no longer visible. It is then raised until visibility is regained. This is known as the secchi depth. By multiplying this depth by a factor of 3 the euphotic depth is measured. The same person should always operate the secchi disk as this avoids differences in people’s vision affecting the reliability of the results.

 


Figure 2.2. A Secchi disk

 



Side Scan Sonar:

The side scan sonar, (figure 2.3) uses sonar pulses to create a detailed image of the seafloor , and is used to identify any major bed features and sediment types. The transducer creates ultrasonic waves form both sides of the tow fish to create a swath, totalling 150m. The returning waves are received and printed out to create a visual image of the sea floor. The quality of the image is dependent on the frequency of the waves. The higher the frequency the better the quality, however the range becomes smaller. The side scan can either be mounted directly onto the boat or as a tow fish. The tow fish is the more favourable method as this eliminates problems such as boat movement, and allows more flexibility for deployment within the water column, i.e. eliminating wave interaction with the equipment.



Plankton Net:

These are used in the collection and then sampling of plankton from within the water column. The net and collection bottle are towed behind the vessels using the ‘A’ frame. The net mesh size was 200µm, so anything above this size is caught in the net. The net can be closed at any depth using the lead shot messenger allowing samples to be taken at predetermined depths.

 


Figure 2.3. A Towfish Side Scan Sonar

 



Van Veen Grab:
Van Veen grabs (figure 2.4) are used to identify sediment composition of the sea floor, and to identify different fauna. The samples were passed through different sized mesh sieves to help identify the types of sediment present and to help find the smaller faunal species.

YSI Probe:
This is a multi-sensor probe that allows the simultaneous collection of Salinity, pH, dissolved oxygen concentration and temperature. It is very easy to use as it can be deployed over the each of a vessel to any depth, only limited by cable length. The readings are shown on a handheld digital display.

 


Figure 2.4. A Van Veen Grab in use


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3. Laboratory Analysis Methods


 

 

Below are outlines of the various methods used in the laboratory for chemical and biological analysis of samples collected on the offshore and estuarine boat practicals.

Nitrate Analysis Method:
The nitrate was analysed using flow injection analysis, strongly based on the method outlined by Johnson and Petty (1983). The results were displayed on chart recorder. The full scale deflection was 100mV. The standards used where 1, 5 and 10 molar.

Phosphate Analysis Method:
The phosphate was analysed as per Parsons et al. (1984). The standards used were 0.15, 0.30.0.75 and 1.5 µmol l-1. The samples, standards and blanks were analysed using a using a Unicam 8625 Spectrometer with a cell size of 4cm

Silicon Analysis Method:
The method followed for the analysis of silicate concentration is as outlined in Parsons et al. (1984). This method allows calculation of the Si concentration present in the collected water samples by creating a colour change which is then measurable via Spectrophotometry. From the standards, it was possible to create a calibration curve, from which the equation of the line was used to calculate the concentration of the silicate in our samples via the measured absorbance recorded by the spectrophotometer. The approximate detection limit for the dissolved silica analysis is 0.3uM.

Dissolved Oxygen Analysis Method:
The dissolved oxygen method was analysed using the Winkler method as per Grasshoff, et al. (1999).

Chlorophyll Analysis Method:
The concentration of chlorophyll per sample was analysed using a 10-AU Fluorometer following the method outlined by Parsons et al. (1984).

Phytoplankton Taxonomy Analysis Method:
Samples were transferred to measuring cylinders and left to settle so that the phytoplankton precipitated to the bottom. A vacuum pump with an inverted glass pipette was used to carefully remove all bar the bottom 10ml of sample, trying to ensure that the phytoplankton was not resuspended during the process. The concentrated 10ml of each sample was transferred into an appropriately labelled polypropylene bottle. The 10ml samples were then transferred onto microscope slides and counted and identified with the aid of a taxonomic guide.

Zooplankton Taxonomy Analysis Method:

The samples were mixed to ensure even distribution of organisms. A measure of 10ml of sample was viewed on a Bogorov chamber using a microscope at 50x magnification, with the aid of an identification book. The number of each species present was recorded.

 


 


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4. Offshore Study

 

 

Introduction:

Aims & Objectives:
1. To understand how vertical mixing processes affect the structure and functional properties of plankton communities.
2. To observe the interactions between said measured parameters.
3. To interpret and explain the relationships observed.
 

 
  Action Plan & Equipment:
Collect data from: Callista (incorporating fully equipped wet & dry labs; ADCP).
Using: CTD with Niskin bottle rosette system; Plankton net; Secchi disk.
 
 
  Logistics:
         Date: The surveys were conducted on the 4th July 2007.
         Location: The survey stretched from Mylor (50°09.111N, 005°03.546W) to  50°05.236N, 004°59.343W (see route map).
         Time: 0815GMT-1400GMT
         Tide: HW 0744GMT 4.8m; LW 1408GMT 1.1m.
         Environmental conditions: westerly force 6 rising 8, cloud cover ranging 3/8 to 8/8, scattered showers, sea state moderate. 
 
 
  The Team:
PSO: Rob
General Dogsbody: Alex
Scribe: Dafydd
Wet lab team: Sarah, Katie, Joana, Harriet
Dry lab: Beth
Stern deck team: Elly, Martyn, Kris


 
 
 
 

Offshore Survey Method:

The survey commenced at Mylor (station 1), headed south to Black Rock (station 2), then east to stations 3&4. (figure 4.1).
Resulting from unfavourable weather conditions (i.e. rising force 8 gale) we were forced to alter out original plans to sample in deeper water, only four sample sites could be reached.

At each of the four stations, the following tasks were carried out:
1. A 200µm mesh plankton net (diameter 59cm) was deployed in order to collect zooplankton samples, which were subsequently preserved with formalin solution.


Figure 4.1. Offshore survey
track plot (click to enlarge)

 
 

2. The CTD was deployed for a down-cast, establishing the vertical profile.
3. The Niskin bottles were fired at appropriate depths according to the strategic sampling plan, during the up-cast.
4. The Secchi disk was deployed and cloud cover noted.

Primarily from each Niskin bottle, samples were collected for dissolved oxygen analysis, fixed in preparation for analysis by the Winkler method and subsequently stored within a water bucket. Secondarily, bulk samples were obtained and divided into the following sub-samples:
Nutrients – samples filtered through glass fibre filter (GFF) to remove phytoplankton & particulate matter. Samples refrigerated.
Chlorophyll – water samples filtered through GFF, GFF containing filtrate stored and refrigerated in acetone.
Phytoplankton – Lugols solution added to sample, stored.
Silicate – samples filtered through a pre-flushed GFF, stored in plastic bottles and refrigerated.
The samples were treated and stored as above within the “wet” lab.

For laboratory methods used for analysis of nitrate, phosphate, silicon, dissolved oxygen, chlorophyll and phytoplankton and zooplankton taxonomy, see Laboratory Analysis Methods section

The Callista cruised between stations at a maximum speed of 5kts ensuring appropriate conditions for ADCP use. The electronic data obtained from the ADCP & CTD was monitored and recorded from the “dry” lab. Vertical profiles were constructed and henceforth the sampling strategy was determined in accordance with the position and strength of the thermocline or the chlorophyll maxima.
 

 
 
  CTD Data Analysis:
 
 
 

Station 1:
At station 1 (figure 4.2) the temperature values decreased with depth whereas the salinity and the density increased with depth. The temperature minimum was approximately 12.75°C at a depth of 21m. The salinity maximum was 35.25 at a depth of 19m. At the same depth (19m), the density was 26.74kgm-3 (maximum value of density). The transmissivity was 3.5m at a depth of 3m which tended to increase slightly with depth.
The fluorometry values were more variable in comparison to the transmissivity values. At a depth of 3m the fluorometry was 1.4volts which increased to about 7m. From 7 to 15m, the fluorometry tended to decrease however from 15.7 to 16m the fluorometry values varied between 1 and 2.35v. From 21.7 and 22m there was a variation of 1.15v.
 


Figure 4.2. Station 1 CTD and chlorophyll plot (click to enlarge)

 
 

Station 2:
At station 2 (figure 4.3) the temperature remained mostly constant between 0.1 and 6m, decreasing then, having a minimum of 12.8°C at a depth of 9.5m, which remained constant until 10.5m depth. The salinity values show an inverted pattern to the temperature values. A maximum of 35.2 at a depth of 10.5m could be seen. The density increased relatively rapidly to about 7m following that, the increase was steadier. The transmissivity value was approximately 3.6 which remained constant with depth. The fluorometry was 1.45 v at a depth of 0.1m and 1.9v at a depth of 5.5m. At a depth of 10.5m the value of fluorometry was about 1.55v.
 


Figure 4.3. Station 2 CTD and chlorophyll plot (click to enlarge)

 
 

Station 3:
At station 3 (figure 4.4) the temperature remained constant between 2-15m at approximately 13°C, decreasing then until 20m depth. Between 20 and 39m the temperature remained constant once more. The salinity remained steady through out the depth with a value of 35.25.
The density increased with depth however from 15 to 17.5m, the density raise was slower when compared with the all density distribution. A thermocline could be seen between 15 and 19m depth. The transmissivity was constant between 2 and 16.5m depth, however from 16.5 to 39m the values of transmissivity tended to decrease. The fluorometry increased between 2 and 8m. From 8 to 15m and from 19 to 39m the fluorometry decreased
remaining mainly constant from 19 to 39m depth with approximately 1.5v.


Figure 4.4. Station 3 CTD and chlorophyll plot (click to enlarge)

 
 

Station 4:
At station 4  (figure 4.5) the temperature was approximately 12.92°C at a depth of 5m however at a depth of 47m the temperature was about 12.4°C which means that the temperature decreased with depth.
The salinity remained constant along the depth and the density tended to increase dramatically through the depth. There was an evidence of a thermocline at about 26m depth. The transmissivity was constant between 5 and 21m depth though from 28 to 39m depth the transmissivity tended to decrease. The fluorometry was 1.7v at a depth of 5m. Between 6 and 9m the value of fluorometry increased 0.75v moreover from 9 to 39m there was a decrease of approximately 1.2v. 
 


Figure 4.5. Station 4 CTD and chlorophyll plot (click to enlarge)

 
 

Chlorophyll:
Chlorophyll concentrations obtained in the lab correspond well with the values shown by the fluorometer (see figures 4.2 - 4.5). Stations 1 and 2 show little variation with depth, for example station 1: 2.3-3.2μg/L and station 2: 2.9-3.4μg/L. Stations 3 and 4 both show notable decrease with depth in particular below the thermocline. Station 3 shows the highest chlorophyll values with values >5μg/L above the thermocline (16m), decreasing below to 1.9μg/L at 39m. At station 4 chlorophyll is lower (<4μg/L) decreasing from 3.3μg/L (11m) to 0.9μg/L below the thermocline.
 

 
 
 

ADCP Data Analysis:

Mylor Transect:
Table 4.1 clearly shows a more pronounced net negative (ebbing) surface flow (–240m³/s) than those observed at the bottom of the water column (–104m³/s). This was predominant. This would be expected as the estuary was in the initial stages of ebbing when the transect began at 09:37GMT. Figure 4.6 displays a southerly ebbing flow of surface waters towards the boundaries of the estuary with values reaching up to 0.3m/s and directional average of between 150° and 220° when nearing the shoreline. Less extensive current velocities were experienced during the middle sections (deeper waters) of the estuary where influences due to basin topography on current flow were less.

 
 Discharge (Bottom) Left to Right
Top Q -240.69 [m³/s]
Measured Q -1138.25 [m³/s]
Bottom Q -104.41 [m³/s]
Left Q -17.5 [m³/s]
Right Q -46.44 [m³/s]
Total Q -1547.3 [m³/s]
Table 4.1. Mylor transect bottom flow
 
 

ADCP data of the average backscatter within the water column (Figure 4.6 ), shows a small section of weak inflowing salt water close to the basin floor contrasting to the rest of the estuary where the outflow of less dense fresh water is predominant. This would be expected as a high water of 4.8m occurred at 07:44 and the transect began at 09:37, suggesting that the estuary was in the initial stages of ebbing. A southerly ebbing flow of surface waters towards the boundaries of the estuary with values reaching up to 0.3m/s and directional average of between 150° and 220° when nearing the shoreline.

 


Figure 4.6. Average backscatter
at Mylor (click to enlarge)

 
 
Black Rock Transect:
Figure 4.7, The velocity direction plot, indicates a southerly flow of surface water during an ebbing tide, supported by the data in table 4.2 showing a net surface water flow of -742.39[m³/s].  There appears to be a small wedge of denser salt water still flowing into or remaining stationary at the base of the water column just about the estuary bed. This can be seen in the average backscatter plot by the increase in returning signals from this point. The ship track plot correlates closely with the previous data confirming an ebbing tide and southerly surface water flow at the mouth of the estuary.

Transect between Stations 3 and 4:
Figure 4.8, the plot of average backscatter, shows clear differences in the water column structure. Combining this information with that observed in the velocity magnitude plot (figure 4.9), the existence of a frontal system becomes apparent. There are distinct variations in the direction of current movement between the well mixed coastal side of the front and the more stratified conditions seen over the frontal boundary.

Transect after station 4:
Backscatter plots from station 4 (figure 4.10), located the furthest offshore of all the stations sampled, appear to suggest a stratified water column. The depth of the thermocline was similar to that recorded by the CTD. The ADCP velocity data shows a faster southward flow of up to 0.4m/s on the surface. The velocity magnitude and direction graphs (figures 4.11 and 4.12) show that the denser layer, closer to the bottom contours, is moving slower in an average direction of around 270°. This contrasts to the warmer, less denser surface layer in the water column moving in a more southerly direction at speeds of up to 0.4m/s.

 


Figure 4.7. Velocity direction plot at Black Rock (click to enlarge)

   Discharge (Bottom) Left to Right
Top Q -742.39 [m³/s]
Measured Q -3074.62 [m³/s]
Bottom Q -307.21 [m³/s]
Left Q -84.7 [m³/s]
Right Q -81.18 [m³/s]
Total Q -4290.1 [m³/s]

Table 4.2. Black Rock transect bottom flow

 
 
Figure 4.8. Transect 3 average backscatter  (click to enlarge)

Figure 4.9. Transect 3 velocity magnitude (click to enlarge)

Figure 4.10. Station 4 average backscatter (click to enlarge)

Figure 4.11. Transect 4 velocity magnitude (click to enlarge)

Figure 4.12. Transect 4 velocity direction (click to enlarge)
`
 
  Nutrient Analysis:
 
 


Figure 4.13. Nitrate at all stations
(click to enlarge)

Nitrate:
Figure 4.13 shows the nitrate concentrations measured at each station. Stations 1 and 2 show the highest nitrate concentrations, ranging between 7 and 11μmol/L whilst stations 3 and 4 offshore show concentrations below 7μmol/L. Stations 3 and 4 show little change with depth in comparison with stations 1 and 2 which are much more variable.
The variations seen at stations 1 and 2 can most likely be attributed to estuarine location of these stations and the variability of this environment. Nitrate concentration is lowest above the thermocline at station 4 which may reflect utilisation by phytoplankton in the mixed layer. However, the changes in concentration are relatively small so clear conclusions are difficult to draw.

 
 


Figure 4.14. Phosphate at all stations
(click to enlarge)


Phosphate:
Stations 1, 3 and 4 (figure 4.14) showed increase with depth from about 0.1μmol/L to concentrations greater than 0.3μmol/L. Station 1 showed very little variation with depth varying little from 0.1μmol/L.
This may suggest nutrient depletion in surface waters, however as variations are small (<0.4μmol/L) it is difficult to draw any definitive conclusions from this data.
 

 
 


Figure 4.15. Silicate at all stations
(click to enlarge)

Silicate:
Silicate concentrations at stations 1 and 2 (figure 4.15) remain relatively constant with depth at around 3.5μmol/L. Stations 3 and 4 showed a much greater range in silicate concentration, varying from around 2μmol/L at the surface and increasing with depth to greater than 4μmol/L. The increase in silicate with depth coincides with the thermocline suggesting utilisation by phytoplankton such as diatoms above the thermocline and remineralisation below the thermocline. Silica is in highest concentration in fresh water, and therefore it may be expected to be found in higher concentrations closest to the estuary and freshwater inputs as seen stations 1 and 2.
 
 
 

Phytoplankton taxonomy:

The phytoplankton population measured in the laboratory is dominated by diatoms at all stations with a small contribution by dinoflagellates at all depths at station 1 and at 2m in station 3. Cilliates contribute to the phytoplankton population only at station 1 at 6m, this is shown in figure 4.16. Figure 4.16 also shows, in correlation with the chlorophyll analysis, the highest phytoplankton populations at all depths in station 3 reaching a maximum of 169 cells/L at 8.5m, all of which were diatoms. The smallest phytoplankton population is found at station 4, where cell counts reach a maximum of 35.67 cells/L at the surface which decreases to 6.33 cells/L at 43m.
Reflecting the concentration of chlorophyll the number of phytoplankton cells counted at station 1 and 2 are similar to each other. At station 1 the phytoplankton population is highest at 6m where around 75 cells/L were counted, mainly consisting of diatoms with some dinoflagellates and ciliates. At station 2 the population of phytoplankton was highest at 2m where 89 cells/L were counted all consisting of diatoms. At 11m at station 2 the phytoplankton population was lowest at 32 cells/L.

Figure 4.17 shows the contribution that each phytoplankton species counted has on the population. At all stations the diatom Chaetoceros dominated the phytoplankton population, with some contribution by Rhizosolenia sp.
Figure 4.18 highlights the relative contribution of other species of phytoplankton, this shows a greater range of species at station 1 at 6m and 23m. A similar range of species can be seen in station 3 at 2m. Other species include the diatoms See figure for details.
The Shannon diversity index calculated for each station shows greater diversity at station 1 with a mean index of 1.37. Diversity is similar at stations 2 and 3 with values of 1.01 and 0.93 respectively. Diversity is significantly lower at station 4 with a mean value of 0.59, a difference from stations 1 and 2 that is greater than 2 standard deviations about the mean of the cell counts from station 4.
Multivariate Statistical analysis of the phytoplankton population at all the stations shows no significant difference between the stations. This is seen in figure 4.19 and figure 4.20 as well as an ANOSIM statistic (R) of 0.27. However, a pairwise test with stations 1 and 4, and, 2 and 4 gives a higher R statistic (0.446 and 0.415 respectively) showing less similarity significant at a 0.1% significance level.
 

 
 


Figure 4.16. Stack bar chart showing relative sizes of diatom, dinoflagellate and ciliate populations
(click to enlarge)


Figure 4.17. Contribution of phytoplankton species to total population
(click to enlarge)


Figure 4.18. Transformed (fourth root) number of phytoplankton individuals in population
(click to enlarge)

 
 



Figure 4.19. Dendogram comparing offshore
phytoplankton communities (click to enlarge)
 



Figure 4.20. MDS ordination comparing offshore
phytoplankton communities (click to enlarge)
 

 
 
 

Zooplankton Taxonomy:

Figure 4.21 shows the relative size of the population at each station was dominated by the phylum Athropoda such as Copepods. The greatest population of zooplankton was found at station 1 were a concentration of approximately 9500 individuals/m3 were observed. The lowest population of zooplankton was found at station 4 where the concentration was approximately 1800 individuals/m3. The population at stations 2 and 3 were relatively similar with concentrations of approximately 4000 individuals/m3 and 5600 individuals/m3. A large range of zooplankton species were observed, see figure 4.22 for details.
The Shannon diversity index for the zooplankton population at each station was very similar, with a maximum index at station 2 of 2.31 and a minimum at station 4 of 2.01. This is not a significant difference. The abundance at station 4 (23.75) however is significantly lower than the abundance at the other three stations (mean of 38.67). This reflects the low phytoplankton population at this station. However, the large population of phytoplankton at station 3 does is not reflected by a large zooplankton population, indicating a recent growth in phytoplankton.
This difference reflected by the multivariate analysis of the zooplankton population. This showed a slight separation of station 4 from the other stations on the MDS ordination (see figure 4.23) suggesting a dissimilarity of station 4 from the other stations. This difference is also evident in figure 4.24 which shows that the samples from station 4 are similar to the other stations at just below a 60% similarity level. This difference is even more clear as shown by the pairwise tests performed as part of the ANOSIM test. The pairwise test gave an R statistic of 0.95, 0.83 and 0.91 when comparing stations 1 and 4, 2 and 4, and, 3 and 4 respectively.
 

 
 



Figure 4.21. Stack bar chart showing contribution of different
species to offshore zooplankton communities (click to enlarge)



Figure 4.22. Transformed (fourth root) number of zooplankton
individuals in population (click to enlarge)

 
 



Figure 4.23. Dendogram comparing offshore
zooplankton communities (click to enlarge)
 



Figure 4.24. MDS ordinationcomparing offshore
zooplankton communities (click to enlarge)
 

 
 
 

Discussion:

The chlorophyll concentrations measured by the lab fluorometer supports the data recorded by the fluorometer on the CTD. Each show greater chlorophyll concentrations at station 3, with a large chlorophyll maximum between 5 and 15m, suggesting greater primary production in this region. At station 4 there is a chlorophyll maximum at 10m, below which the chlorophyll concentration falls, as also shown by the lab analysis of the chlorophyll data. The CTD fluorometer shows conservative behaviour by chlorophyll in the water column at stations 1 and 2, as did the laboratory analysis.

The phytoplankton population analysis shows greater numbers of phytoplankton at station 3, which reflects findings given by fluorometer. The smallest phytoplankton population was seen in station 4, where there were lower chlorophyll concentrations on average in the water column. All stations are dominated by diatoms with some ciliates and dinoflagellates which particularly prefer less well mixed waters (Bernardi Aubry et al. 2004). This supports findings demonstrated by Rodriguez et al. 2000. There was no significant difference between the populations found at each station, however there was some small difference between station 4 the other stations. In the phytoplankton population this difference lies in the diversity of the population, at station 4 the diversity of the phytoplankton population is significantly lower than the other stations. This suggests a more stress full environment at station 4.

These unfavourable conditions arise as a result of large amounts of mixing in the surface waters creating a mixed layer deeper than the euphotic zone. This is seen in the temperature profile at station 4 which shows that there is a thermocline at 25m depth. Therefore, the depth of the euphotic zone shown roughly using a Secchi disk (table 4.3) as 15m, is shallower than the depth of the mixed layer. This implies that phytoplankton would be mixed away from the euphotic zone on some occasions limiting photosynthesis, forcing a chlorophyll maximum to form above the thermocline in water that is seen to be nutrient limited.

Station Secchi Depth 1% Depth Attenuation Coefficient
  (m)   (m-1)
1 4.5 13.5 0.32
2 5.5 16.5 0.26
3 6.5 19.5 0.22
4 5.5 16.5 0.26
Table 4.3. Secchi depths, euphotic (1%) depth and attenuation coefficient at all offshore stations.

An increase in nitrate with depth at station 3 would tend to suggest a depletion of nutrients in the surface waters by phytoplankton growth, most notably immotile diatom species. At station 3 the depth of the euphotic zone is as deep as the depth of the mixed layer, creating very favourable conditions where nutrients mixed across the thermocline can be utilised for photosynthesis. Within the mixed layer silicate concentrations are low (~1.5μmol/L) suggesting utilisation by diatom species, shown to be present by high chlorophyll levels (>5μmol/L) in the top 20m and phytoplankton taxonomic analysis.

As a result there is a very large and diverse phytoplankton population at station 3. Similarly at stations 1 and 2 where the water column is shallower and the depth of the euphotic zone is similar to the proceeding stations, a significant phytoplankton population can from with a high diversity particularly at station 1 as no mixing occurs below the euphotic zone.
The low diversity of phytoplankton at station 4 is reflected by a zooplankton population of lower abundance than that at the preceding stations. This is highlighted as the zooplankton population at station 4 was shown to be significantly different to the zooplankton population at the other stations. The offshore stations (3 and 4) being at a greater depth are more effected by oceanic processes. This may have resulted in a greater range of physiochemical processes effecting the observed concentrations of nutrients.

 

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5. Estuarine Study

 

Introduction:

Aims & Objectives:
1.
To understand how vertical mixing processes affect the structure and functional properties of plankton communities.
2. To observe the interactions between said measured parameters.
3. To interpret and explain the relationships observed.

Action Plan & Equipment:
Collect data from: Bill Conway (incorporating fully equipped wet & dry labs; ADCP) and Ocean Adventure RIB.
       1.
Bill Conway Equipment:
           Using: CTD with Niskin bottle rosette; ADCP; T/S probe; Plankton net; Secchi disk.
       2. RIB Equipment:
           Using: a single Niskin bottle on the Rib; Plankton net; Secchi disk, YSI probe.

Logistics:
       1. Bill Conway:
           Date: The surveys were conducted on the11th July 2007.
           Location: The survey stretched from Fal River (50°13.551N, 005°00.092W) to 50°09.127N, 005°01.785W (see figure 5.1).
           Time: 0828GMT-1341GMT

       2. RIB:
           Date: The surveys were conducted on the 11th July 2007.
           Location: The survey stretched from Malpas pontoon (50°14.687N, 005°01.373W) to 50°12.549N, 005°01.682W Turnaware point (see figure 5.1).
           Time:
0831 GMT – 1316 GMT

       Tide: HW 1416GMT 4.6m; LW 0823 GMT 1.1m. (Neap)
       Environmental conditions: NW backing SW force 4/5 occasionally 6, sea state slight moderate
, cloud cover ranging 1/8 to 4/8

The Team:
PSO:
Katie
CTD deck: Rob
CTD computer: Elly, Joana
Scribe: Dafydd
Lab team: Sarah, Harriet
RIB: Alex, Beth, Kris, Martyn


 

 
 
 

Estuarine Survey Method:

1. Bill Conway:
The survey commenced within the Fal River (station 1), heading south to Smugglers Cottage (station 2), Turnaware (station 3), Restronguet (station 4), Penarrow (station 5), and terminated at Black Rock (station 6). (See figure 5.1).

The following tasks were carried out:
     1. A 200µm mesh plankton net (diameter 50cm) was deployed at 2kts
        in order to collect zooplankton samples, which were subsequently
        preserved with formalin solution. Stations 2 and 6.
     2. The CTD was deployed for a down-cast, establishing the vertical
        profile. Stations 2,3,4,5 and 6. At station 1 the deck pump was used
        to measure the temperature and salinity of the surface water (1m
        deep).
     3. The Niskin bottles were fired at appropriate depths according to the 
        strategic sampling plan, during the up-cast. Also a T/S probe was
        used to measure the temperature and salinity of the bulk samples.
        Stations 2,3,4 and 5.
     4. The Secchi disk was deployed. Stations 2,3,4,5 and 6.
     5. ADCP transects across different areas across the estuary, to 
        measure the vertical and horizontal profiles. Stations 2,3,4,5 and 6.

The Bill Conway cruised along transects at a maximum speed of 2kts ensuring appropriate conditions for ADCP use. The electronic data obtained from the ADCP & CTD was monitored and recorded from the “dry” lab. Vertical profiles were constructed and henceforth the sampling strategy was determined in accordance with the position and strength of the thermocline.

2. Rib:
The RIB was used to sample the upper estuary in order to access shallower water. The survey commenced at Malpas (station 1), heading North to Woodberry Point (station 2), Northwood (station3), and then onto station 4 and Turnaware (station 5). (figure 5.1)

The following tasks were carried out:
     1. A 200µm mesh plankton net (diameter 50cm) was deployed at
        0.5kts in order to collect zooplankton samples, which were
        subsequently preserved with formalin solution. Stations 2
     2. The YSI probe was deployed to measure the vertical profile of the
        upper estuary. Stations 1-5
     3. A Niskin bottle was lowered at appropriate depths according to the
        strategic sampling plan, during the up-cast. Stations 1-5
     4. The Secchi disk was deployed. Stations 1-5

 

 


Figure 5.1. Navifisher plot showing RIB (YSI) and Bill Conway (CTD, ADCP) sample stations and transects.

 


Table 5.1. Key for Navifisher plot (figure 5.1)

 
  CTD Data Analysis:
 
 
 

Bill Conway Station 2 (figure 5.2) outside Fal 17 – 25 psu dominated by FW from fal, rest of sites 34-35 salinity, due to the tidal flooding of the estuary at the time of the survey. Fluorometry and transmissivity values remained fairly constant with depth throughout all stations, with the highest values occurring at stations 5 and 6 (figures 5.5 & 5.6). At station 6, transmissivity and fluorometry fluctuate below 15m, with a slight overall decrease.

Bill Conway station 3 (figure 5.3), chlorophyll concentrations were approximately 6-8 mg l-1, displaying a slight increase with depth. Chlorophyll values were consistently below 1mg l-1 at stations 4 (figure 5.4) and 5, and highest station 5 10m, with a value of 9.26mg l-1. Salinity values fluctuate little between stations, with values of approximately 34-35psu.

Temperature values decreased with increasing depth at all stations, correlating closely with increasing density values. Weak diurnal thermoclines appear to be present at most stations


Figure 5.2. Station 2 CTD and chlorophyll plot (click to enlarge)

Figure 5.3. Station 3 CTD and chlorophyll plot (click to enlarge)

 
 


Figure 5.4. Station 4 CTD and chlorophyll plot
(click to enlarge)


Figure 5.5. Station 5 CTD and chlorophyll plot
(click to enlarge)


Figure 5.6. Station 6 CTD plot
(click to enlarge)

 
 
 

YSI Data Analysis:
 

 
 

The lowest salinity was found to occur at RIB station 1 (figure 5.7), the most riverine sample point. Station 1 also displayed the most pronounced temperature and salinity gradients between 0m and 1m, 22psu to 33psu and 16.7oC to 14.7o6 suggesting a diurnal thermocline. RIB station 2 (figure 5.8) displayed relatively constant temperature and salinity values, with no apparent thermocline or halocline.

RIB stations 3 and 4 (figures 5.9 & 5.10) appear to have a diurnal thermocline present at 2m. The halocline of rib station 3 occurs just above 2m, whilst the halocline of rib station 4 occurs at 2.5m. Rib station 5 (figure 5.11)displays a clear diurnal thermocline at 2m and a halocline just below 2m.

A front could be seen moving upstream at station 3, as seen in figure 5.12, however it was not possible to take samples as it was thought that the front was too thin
 


Figure 5.7. Station 1 YSI and chlorophyll plot (click to enlarge)

Figure 5.8. Station 2 YSI and chlorophyll plot (click to enlarge)
 

 
 


Figure 5.9. Station 3 YSI and chlorophyll plot
(click to enlarge)


Figure 5.10. Station 4 YSI and chlorophyll plot
(click to enlarge)


Figure 5.11. Station 5 YSI and chlorophyll plot
(click to enlarge)

 
 



Figure 5.12. Tidal front at RIB station 3 shown by surface scum

 
 
 

ADCP Data Analysis:
 

 
 

Station 1
A patch of dense, more saline water can be observed flowing along the bottom of the channel. This feature can also be observed on the velocity magnitude plot, coinciding with the backscatter. It shows a higher velocity at 0.25m/s in comparison with the slower velocities of the rest of the water column. This also correlates to the tidal state as at the time that this station was sampled it was only a few hours after low tide.

When looking at the ship track plot, the dominant current is flowing northwards into the estuary showing that major velocity direction is the result of flow into the estuary on the incoming tide

 
 


Figure 5.13. ADCP velocity direction, velocity magnitude, average backscatter
and ships track plots for Station 1 (click to enlarge)

 
  Station 2:
The ADCP data for station 2 (figure 5.14) shows that the
speed of the incoming tide in the mid to bottom layer of the water column has increased to an average of around 0.325m/s indicating the flooding tide has amplified. The interface between the fresher and more saline water has risen to about 5m depth. The direction of the current flow has changed from north to a north-easterly direction, however this may be due to changes in basin morphology.
 
 


Figure 5.14. ADCP velocity direction, velocity magnitude, average backscatter
and ships track plots for Station 1 (click to enlarge)

 
  Station 3:
The transect took place at 10.26GMT. The V-shaped trench shows a faster current than the shallower more western parts of the estuary.  At this station the amount of freshwater input has been greatly reduced. 
 
 


Figure 5.15. ADCP velocity direction, velocity magnitude, average backscatter
and ships track plots for Station 1 (click to enlarge)

 
 

Station 4:
The velocity of the current within the channel has reached 0.400m/s at 15.00m depth .The velocity magnitude and direction plots show a three layer water column.

 
 


Figure 5.16. ADCP velocity direction, velocity magnitude, average backscatter
and ships track plots for Station 1 (click to enlarge)

 
 

Station 5:
The strongest currents are in the V-shaped trench and on the Eastern boundary moving in a North Easterly direction . The Eastern boundary current in the middle of the channel is moving north .  The velocity magnitude plot shows a parcel of water from 7m to surface moving at an average speed of 0.35m/s on the Eastern boundary. The backscatter plot appears to indicate a uniformly mixed estuary apart from a small surface layer on the eastern side. The velocity magnitude plot also shows very similar results.  The increased water speed in the vertical column towards the eastern boundary is caused by the passing of another motor vessel.

 
 


Figure 5.17. ADCP velocity direction, velocity magnitude, average backscatter
and ships track plots for Station 1 (click to enlarge)

 
 
  Nutrient Analysis:
 
 


Figure 5.18. Nitrate at all stations
(click to enlarge)

Nitrate:
RIB -
The nitrate concentrations for the upper estuarine concentrations (RIB) ranged from 4.5mmol l-1 to 76mmol l-1 between stations. For all stations the highest nitrate concentration occurred at the surface, with concentrations decreasing with increasing depth remaining approximately constant. The highest nitrate concentrations were found to occur at the surface of station 2, and the lowest nitrate concentration at station 5. Concentrations decreased with increasing salinity, with the exception of station 1.
Bill
Conway – Nitrate concentrations were found to be highest at the surface, remaining approximately constant with increasing depth. The nitrate concentrations for stations 1a and 1b were very high, with concentrations of 146.8mmol l-1 and 124.9mmol l-1 respectively. Nitrate concentrations decreased with increasing salinity, and the values for stations 3, 4 and 5 (highest salinity) were very similar, with surface values ranging from 7.8 µmol l-1 to 8.6µmol l-1.

 
 


Figure 5.19. Phosphate at all stations
(click to enlarge)


Phosphate:
The highest phosphate concentration, 0.014mmol l-1 were found at Bill Conway station 1, while the lowest phosphate concentration, 0.0065µmol l-1 was found at Bill Conway station 3. Concentrations showed little variation with increasing depth.
 

 
 


Figure 5.20. Silicate at all stations
(click to enlarge)

Silicate:
Ribs - Silicate concentrations at the river end (lowest salinity) were very high, with a concentration of over 100 μmol/L. In comparison the river samples taken from the rib were much lower at below 20 μmol/L. Stations 2, 4 and 5 all decrease in concentration with depth with Station 2 showing the largest range of just below 20 μmol/L to about 4 μmol/L within the surface 6m of the water column. Station 3 however shows a constant distribution through the water column with a concentration of around 22 μmol/L between 4m and 14m.
Bill Conway - Silicate concentrations at stations 1a b and c (all sampled at 10m depth) vary between 25 and 61μmol/L despite being sampled at sites very close to each other. Station 2 showed a decrease in silicate concentration, varying from around 23μmol/L at the surface and decreasing with depth to a value of 8μmol/L. Stations 3, 4 and 5 (those closest to the sea) have very consistently small Silicate concentrations throughout the water column suggesting high mixing in this area.
 
 

 

 

Estuarine Mixing Diagrams: 
Non-conservative behaviour was exhibited by nitrate, phosphate and silicate. Nitrate (figure 5.21) and silicate (figure 5.22) both showed removal at salinities of around 20 to 30. Nitrate showed a particularly low value of 15.9µmol/L at a salinity of 17.9 occurring in the Fal outflow (Bill Conway Station 1c) suggesting that the Fal may have a low nitrate concentration. Nitrate and silicate removal is the result of phytoplankton, in particular diatom growth for the removal of silicon. Phosphate, however, showed significant addition (figure 5.23), in particular around the Fal inflow. Significantly increased phosphate concentrations may be the result of anthropogenic inputs from sewerage or agricultural runoff.
 

 
 
Figure 5.21. Nitrate estuarine mixing diagram (click to enlarge)

Figure 5.22. Silicate estuarine mixing diagram
(click to enlarge)

Figure 5.23. Phosphate estuarine mixing diagram
(click to enlarge)
 
     
 

Phytoplankton taxonomy:

Figure 5.24 shows the community structure of the phytoplankton population at each of the sampled stations within the Fal system. This shows that the greatest phytoplankton population was present at station 3 sampled by the RIB with cell numbers in the region of 1100 cells/ml. The population at this station was dominated by Nitzchia sp. with some Chaetocerus sp. present. The population at RIB station 1 was approximately half the population at RIB station 3 with equally dominant populations of Chaetocerus sp. and Nitzchia sp with 303 cells/ml of Chaetocerus and 275 cells/ml in a total population of around 635 cells/ml. Of the RIB samples these were the most riverward stations sampled.
The numbers of phytoplankton counted at the remaining stations suggest a much lower phytoplankton populations, all dominated by Chaetocerous sp. Of the Bill Conway samples the greatest population was present at station 4 near the out-let for the Restronguet Creek, the population at this point was in the region of 280 cells/ml. As with the remaining stations, station 4 was dominated by Chaetocerous sp.
Stations 5 RIB and 3 Bill Conway were both at Turnaware Point. The samples at each of these stations contained populations of similar size (~180 cells/ml and ~140 cells/ml) with a more diverse range of species present at station 3 Bill Conway. Figure 5.25 shows the relative contribution of each species to the phytoplankton population at each station, for details of species present see the graph.
 

 
 


Figure 5.24. Contribution of phytoplankton species to total population
(click to enlarge)


Figure 5.25. Transformed (fourth root) number of phytoplankton
individuals in population (click to enlarge)

 
 
 

Zooplankton Taxonomy:

Figure 5.26 shows the community structure of the zooplankton populations at each of the stations sampled by the RIB and the Bill Conway. This shows populations much lower than those present in the offshore environment despite the greater numbers of phytoplankton present in the estuarine system. The trawl taken at station 2 Bill Conway contained greatest numbers of zooplankton with approximately 260 individuals/m3 (compared to numbers averaging 5000 individuals/m3 at the offshore stations). As with the offshore system the zooplankton population was dominated by Arthropods such as Copeopods.
The most riverward trawl (Station 2 RIB) produced the fewest zooplankton, with approximately 100 individuals/m3. The most diverse sample was collected at station 6, this was the most seaward station. Figure 5.27 shows relative contribution of each species to the zooplankton community. For details of the species present see the graph.

 
 


Figure 5.26. Contribution of zooplankton species to total population
(click to enlarge)


Figure 5.27. Transformed (fourth root) number of zooplankton
individuals in population (click to enlarge)

 
 
 

Discussion:

The high nutrient concentrations found at Bill Conway station 1 can be attributed to the proximity of the station to the Fal River. This inputs fresh water and high concentrations of nutrients from sources such as agriculture to the Fal system.  The surface nutrient values at Bill Conway station 3 are high whilst the deeper water displays low nutrient levels suggesting a flow of nutrient rich river water supplied by the Lamouth and Cowlands Creek, above nutrient poor sea water.

The low nutrient values found at Bill Conway stations 4 and 5 can be attributed to the inflow of nutrient poor salt water and the proximity of the stations to the mid-region of the estuary. Station 2 Bill Conway has greatest zooplankton population density approx 260 individuals m-2. Rib Station 2 had the lowest zooplankton population density approx 100 individuals m-2. The greatest phytoplankton population density occurred at rib station 3, which was dominated by the diatom Nitszchia longissima. Bill Conway Station 3 had a relatively diverse phytoplankton community with a relatively low population in comparison to other stations; 140 individuals m-2.

The relatively low nutrient levels in the middle of the estuary could be attributed to the high concentration of phytoplankton in this region. This is visible on the theoretical dilution lines of nitrate and silicate, which shows removal. The large numbers of diatoms present in the bloom would remove nitrate for photosynthesis and use silicate to produce their casts. The succession of this bloom would have reduced the level of nutrients, until eventually they became limiting and the bloom would cease. The bloom may have been stimulated a large nutrient inputs as a result of the heavy rain that occurred for two weeks prior to the study. This would increase the land runoff of nutrients such as nitrate into the estuarine system. The bloom may have initially been stimulated by the high levels of sun light that occurred during the weekend before the study. On the day of the survey, conditions were warm and sunny which may have stimulated the formation of the diurnal thermocline in the upper estuarine stations sampled by the rib.

The low salinities sampled by Bill Conway at Stn 1 can be attributed to the influx of FW from the river Fal. The rest of the Bill Conway sites were found to have salinity values of 34-35 psu, this can be explained by tidal flooding of the estuary at the time of the survey. Although weak thermoclines appear to be present at most stations, the sunny conditions of the day of survey may have induced a temporary state of stratification, hence the apparent presence of a diurnal thermocline. However, the greatest proportion of the data and observations are indicative of a parially mixed body of water with a slight two layer flow observed with the ADCP.  The dynamic nature of the partially mixed estuarine environment such as the Fal system and the variability caused by factors such as the weather would create a spectrum of possible conditions effecting the vertical stratification of the estuary, and hence greatly effect the distribution of nutrients and phytoplankton.

 


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6. Geophysics

 

Introduction:

Aims & Objectives:
To survey the area immediate to the south of the mouth of the Helford estuary, in order to obtain data concerning biotic and abiotic characteristics of the sediment, and to decipher the topographic features of the seabed.  

Action Plan & Equipment:
1. To collect data using equipment aboard MV Grey Bear.
2. To focus on the Manacles, an area of specific interest to the organisation: Natural England.
3. To perform transects using side scan sonar and to obtain grab samples from four different sites to determine the biotic and abiotic characteristics of the sediment.

Logistics:
Date: The surveys were conducted on the 7th July 2007 aboard the MV Grey Bear.
Location: The survey commenced at 
50° 05.9554N  005°03.2732W. At this point the “fish” was towed behind the boat and then calibrated. Survey ended at 50°04.203N  005°04.246W. Specific details of each line and grab sites can be found later in this section.
Time: 0800 GMT - 1540 GMT
Tides: 
HW1 0957 GMT 4.7m
              LW2 1617 GMT 1.5m
Environmental conditions: sunny, cloud cover 3/8, west/northwest force 3-4, sea state slight.

The Team:
Harriet was PSO for the day and all team members took turns in completing each task on the boat, including data logging, spotting vessels which could disrupt the sidescan and analysing the side scan images produced.


 

 


 

 
 

Geophysics Survey Method:

The survey was started at the co-ordinates 50° 05.9554N  005°03.2732W. At this point the “fish” was towed behind the boat and then calibrated. At 9.27 GMT the first line was started. In total 7 lines were surveyed running parallel to each other creating a rectangular grid. Each line was 2km in length and the swath width covered 75m each side of the tow fish. Each line slightly overlapped the previous one by approximately 10m ensuring no seafloor features were missed.  Spotters on deck were used to record the position of buoys and boat traffic in our range which could have interfered with the side scan and affected our results. The table below shows the times and locations for the start and end of each line:

Time (GMT) Detail Latitude Longitude
0927 Start line 1 (man012) 50°05.387N 005°03.205W
0947 End line 1 (man012) 50°04.096N 005°03.758W
1005 Start line 2 (man013) 50°04.156N 005°03.818W
1028 End line 2 (man013) 50°05.419N 005°03.267W
1034 Start line 3 (man014) 50°05.400N 005°03.367W
1057 End line 3 (man014) 50°04.144N 005°03.913W
1100 Start line 4 (man015) 50°04.187N 005°03.976W
1124 End line 4 (man015)  50°05.478N 005°03.426W
1129  Start line 5 (man016) 50°05.449N 005°03.517W
1151 End line 5 (man016) 50°04.174N 005°04.070W
1155 Start line 6 (man017) 50°04.700N 005°04.105W
1219  End line 6 (man017) 50°05.483N 005°03.590W
1224 Start line 7 (man018) 50°05.465N 005°03.687W
1247 End line 7 (man018) 50°04.203N 005°04.246W
 
 
 


Grab Sites:

Using the images produced by the sidescan transects, 4 sites of different sediment type were selected for sampling using a Van-Veen grab. For each site the grabs were analysed in relation to the abiotic (sedimentary) and biotic (biological) characteristics.

Grab 1:

Time: 1340 GMT

Sediment Classification:
Fine sand: well sorted, sub-angular grains,
Mica & Serpentine J present, Oxic.
 


Location
: 50°04.208N, 5°04.248W

Fauna:
Errant Polychaete sp.
Bivalves: including
Cerastoderma edule.

 

Grab 2:

Time: 1400 GMT

Location: 50°04.605N, 5°04.100 W

Sediment Classification:
Medium grained, less well sorted, sub-angular grain, dead maerl comprised approximately 40% of sample, bionic material present including shell fragments, metamorphic material present including quartz and slate.

Fauna:
Sedentary suspension feeding polychaete sp.
Errant polychaetes.
Tubiculous polychaetes.
Amphipoda sp.

 

 

 

Grab 3:

Time: 1420 GMT

Location: 50°04.720N, 5°04.065W

Sediment Classification:
Medium grained, less well sorted, subangular grain, dead maerl comprised 40% of sample, bionic material present including shell fragments, metamorphic material present, some conglomerates of mud and larger subrounded pebbles present.

Fauna:
Errant Polychaete sp.
Encrusting red algae
.
Bryozoa sp.
Echinoid sp.
Amphipoda sp.
Tubiculous polychaete, white calcareous tube.
 

 

 

Grab 4:

Time: 1440 GMT

Location: 50°04.897N, 5°03.974W

Sediment Classification:
Poorly sorted ranging from grain diameter 10cm to mud & fine sand. Dead Maerl, shell fragments, large angular shards of metamorphic slate present.

Fauna:
Errant Polychaete sp., Encrusting red algae, Tunicate sp., Amphipoda sp., Tubiculous polychaete, Bivalves, Rhodophyta sp. Live maerl, Crustacea (Shore crab, Fiddler crab, Harbour crab)
 

 

 

 

 

 

 

 



 

 

 

The Wreck of the Volnay:

The possible location of the Volnay Wreck, positioned off Porthallow bay, using the side scan sonar was confirmed through analysis of the sea floor print outs and further background reading. The Volnay sank on the 14th December 1917 after striking a German mine off the Manacles and being towed into Porthallow bay. The vessel lies in around 20m of water, the bow section facing NNE after being extensively broken up due to storm events and planned explosions. 2 large and 1 small “donkey” boiler (1), foreword and to the port side of the wreck, are still in tact and can be seen clearly on the side scan printout. Calculations used have given boiler height estimates of 4.88m, 4.03m and 2.9 m respectively which correspond accordingly to recorded heights documented in literature reports. The rest of the wreck lies relatively flat against the sea bed, with only minor perturbations height recorded using the side scan equipment.



Above:
The Volnay before it sank
Left:
A map of the Volnay wreck site

 
 

 

Main Findings of the Side Scan Sonar:
 
 
 

 
 

Scour Marks: Formed from anchors dredging against the sea floor
 

Bedforms: Megaripples with an average height of 0.16m
 

 
 

 
 

Wreckage: Remnants of the Volnay
 

Sediments and Rocks: Majority of the area covered was rock,
with the remaining sediments being course and fine grained sands.

 
     


Anchor Drag:

1 & 2.   The horseshoe shape displayed above is caused by a ship’s anchor failing to bite the underlying substratum and henceforth being dragged across the seabed
            over a time period thus causing a vast disturbance of the surrounding sediment.

3.          This anchor drag also shows a unique extra drag line and it has been suggested that this has been caused by the ship being moved with the changing tide
            dragging the anchor in a tighter circle.

 


 

 
  Discussion:

The survey undertaken has allowed us to identify the major type of sediment as sand, with rocky outcrops present, especially in the first 3 survey lines. This was known from the side scan sonar and then backed up using the Van Veen Grabs. The grabs also allowed us to identify the different types of fauna present, ranging from bivalves and polychaete’s to shore crabs. The reason for the major differences in fauna are due to the changes in the sediment. The organisms are adapted to   different conditions so that they can only survive in the sediment best suited to their niche. The identification of the wreck, The Volnay, made for interesting analysis as it contrasted to the normal bedforms found.

 
 


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7. Conclusions

 


Offshore Study Conclusion:

Vertical mixing processes in the waters off Falmouth affect the structure and functional properties of plankton communities directly and indirectly. The extent of vertical mixing in the offshore environment near Falmouth created a lot of variability among the plankton communities. The depth of thermocline in this offshore environment gave evidence to the amount of vertical mixing of these plankton communities. For example, lower phytoplankton populations were observed in a region with a deeper thermocline, so that plankton were mixed below the euphotic zone, so that light limited primary production in this region. The evidence of a frontal system observed using the ADCP would have brought about more variability in the observed results, possibly showing more Dinoflagellates which are indicative of the frontal systems in this region.      

Estuarine Study Conclusion:

Nitrate and phosphate show non-conservative behaviour whereas silicate generally show conservative behaviour with some removal. The source of phosphate could be caused by agricultural input whilst the removal of nitrate and some silicate maybe a result of high primary production caused by the diatom bloom (Nitszchia sp.) in the estuary which may have been stimulated by the high rain fall in the weeks preceding the study.  There is a mussel farm located at Northwood that may have affected nutrient levels; however there is no evidence of this in our results.
ADCP and CTD data have show a denser saltwater intrusion at the bottom of the estuary moving in a Northerly direction upstream.  The outward flow of water from the estuary and the inward flow of water as a result of the flooding tide vary throughout the estuary.  The dynamic flow created by bed morphology results in the inner flow to be concentrated in the deep channels. 

Geophysics Study Conclusion:

The data gained from the side scan survey lines identified many features, including a wreck site, which has been identified as The Volnay. The main sediment type identified was sand with bedrock outcrops. Four areas where the sediment types changed from mud through to gravel were found. At sites of interest and significant variation in sediment type observed from the side scan data, Van Veen Grabs were taken. The grabs allowed us to confirm the sediment types and to identify the different faunas in the samples. The fauna ranged from large amounts of Polychaetes in the mud sediment to shore crabs in the gravel and rocky samples. In addition, live Maerl was found in some sample, representing an important discovery for the local environment.
 

 


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8. References

 

Johnson K. and Petty R.L. (1983)  “Determination of nitrate and nitrite in seawater by flow injection analysis”. Limnology and Oceanography 28 1260-1266.

Parsons T. R. Maita Y. and Lalli C. (1984) “A manual of chemical and biological methods for seawater analysis” 173 p. Pergamon.

Grasshoff, K. K. Kremling, and M. Ehrhardt. (1999). Methods of seawater analysis. 3rd ed. Wiley-VCH.

Langston, W. J. et al. (2003)  Fal-Helford. Marine Biological Association Occasional Publication  8

Bernardi Aubry, F. et al. 2004. Phytoplankton succession in a coastal area of the NW Adriatic, over a 10-year sampling period (1990-1999), Continental Shelf Research, 24, 97-115

Rodriguez, F. et al. 2000. Temporal variability of viruses, bacteria, phytoplankton and zooplankton in the western English Channel off Plymouth, Journal of the Marine Biological Association of the United Kingdom, 80, 575-586.   

Leveridge, B.E. Holder, M.T and Goode, A. J. J. 1990. Geology of the Country around Falmouth. British Geological Survey

Websites:
www.cornwall.gov.uk - July 2007
www.diversnet.co.uk - July 2007

 


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