Click the photo's below to enlarge

Rob

Aka "the boss"

Tom

Aka "Fishwife"

Jim

Aka "The Leadloader"

Andy

Aka "Chief Weasel"

Charlie

Aka "The Artist"

Helen

Aka "Maefanwey"

Laura

Aka "Data Minx"

Sam

Aka "Mummy Logbook"

Nick

Aka "Chart-Master"

Sidescan sonar survey

A survey was undertaken in order to study sediment structures of a portion of the Fal estuary between Pendennis Point and Black Rock. The aims were to identify different sediment types and bedforms, outcrops of bedrock, any manmade structures and any ecologically important species such as maerl and eel grass. Sidescan sonar was used in conjunction with grab samples as a method of ground truthing.

The sidescan sonar fish works by passing an electric current through a series of piezoelectric crystals. It works at a frequency of 500 KHz and emits a pulse 8 times a second. The crystals subsequently expand to create a pressure wave (sound wave.) The piezoelectric crystals also receive the reflected signal when it returns from the seabed. The printed trace reveals the strength of return, with a strong return; caused by coarser or harder material showing as darker. Finer material creates a weaker return and therefore a lighter area on the trace. The instrument has a slant range of 75m on each side.


The results showed 4 different bed types, which the grabs confirmed. The side-scan also revealed strikes at 45º NE that were consistent with surrounding terrestrial geology. On comparison with a species map of the Special Area for Conservation, the data suggests the occurrence of live maerl is more widespread than thought.

Transects

6 latitudinal transects were surveyed in order to obtain an overview of the sediment structures. Grab sites were then chosen to further investigate the bed characteristics. The results are as follows:

Bedrock of slate

The side-scan trace showed evidence of surface topography with clearly orientated ridges up to 2.5m in height.
Strong return pulses from ridges indicate dense rock and Grab C found slate to confirm this.

Bedrock with sediment cover

Occasional occurrence of strongly orientated ridges, but mostly monotone featureless return, with medium intensities.

Homogenous sediment

Flat and featureless weaker returns with occasional visible anthropogenic objects.

Rippled sediment

Region with rippled returns of no clear orientation.
Ripples have a wavelength of 2m.
Ripples mostly parallel but showing some divergence and convergence.

Grab Sites

Grab site A

(E:183342, N:030880)
Sediment composition:
40% Weathered mudstone matrix
40% Moderately angular, fragmented black slate - Tabular Morphology, Poorly sorted, ranging in size 50 x 10 mm to 200 x 10 mm. Occasional organic incrustation
18% Fragmented calcareous shell - Poorly sorted, ranging in size from 5 mm to 150 mm
2% Dead maerl - 10 mm diameter

Biological composition: Maerl, Hermit crab, Squat Lobster, Polychaete, Annelid, Rhodaphyta algae and Small crab.

Grab site B

(E:183233, N:31132)
Sediment composition:
80% Dead maerl – Poorly sorted, 5 mm to 50 mm diameter.
18% Calcareous shells - 5 mm to 40 mm diameter
2% Slate shards - < 15 mm in diameter

Biological composition: Maerl, Hermit crab, Squat Lobster, Polychaete, Annelid, Rhodaphyta algae and Small crab.

Grab site C

(E:183278, N:31254)
Sediment composition:
Slate Bed-rock – The Van-Veen grab hit rock and only picked up a few loose slate rocks with algae attached.

Biological composition: Japanese seaweed and Bryozoan

Grab site D

(E: 183538, N: 30811)
Sediment composition:
80% Dead maerl, - Well sorted, heavily broken shingle like structure, ranging in size from 5 mm to 15 mm in diameter
15% Calcareous shells - Varying species, 10 mm to 100 mm in diameter
5% Silty clay




Biological composition: Empty tube worm, Small copepod 4 mm, live maerl, Eel, Squat crab, Chiton and Rhodophyta algae

Strikes

Evidence from grabs and orientation of ridges indicated that the strikes run 45° NE through the bedrock. This orientation is consistent with onshore geology (BGS Memoir 352, 1990). It is probable that the rock in this region is compressed by the Carrick Nape which may be part of the Portscatho Formation.

Estuarine Chemical and biological survey

ADCP transects were carried out across the river Fal and the Fal estuary. In addition to water samples collected via a rosette of Niskin bottles, a CTD cast was undertaken at central points along the transects.  Water samples were prepared on board for further chemical and biological analysis in the lab the next day.

A CTD was used to record temperature, salinity and depth along different transects in the Fal Estuary from the River Fal (50º13.421N, 005º01.505W) to the mouth of the whole estuary (50º08.572N, 005º01.397W); chlorophyll and turbidity were determined by fluorometer and transmissometer measurements respectively. The CTD was used both along the whole transect and placed in the centre of the ADCP transects and deployed for depth recording. Attached to the CTD was a rosette of 6 Niskin water sampling bottles, which were closed at different depths by using an electronic firing system from the boat Bill Conway. From here, data was logged onto a computer notebook.

Seven transects were carried out using the ADCP with the CTD being deployed to obtain depth profiles at all transects, with the exception of transect 7 since the water and weather conditions were unsuitable for such surveying. The Niskin bottles were fired at the bottom, middle and surface at transects 2, 3 and 8, and at the bottom and surface at transects 4, 5, 6 and 7 due to drifting and timing constraints.

Estuarine Phytoplankton Analysis

On the 15/7/06 samples were collected at different sites in the Fal estuary for a 2 minute duration using 200 µm plankton net.  There were four groups / orders identified in the lab. These are: (abundances given in m^3), Diatoms (4325), Dinoflagellates (1005), Ciliates (110) and Silica-flagellates (5).  The total abundance was 5355 and there were 18 species identified, which included 10 Diatoms, 5 Dinoflagellates and 2 Ciliates and 1 Silica-flagellates.  There were 3 dominate types of organisms present within the estuary and there was little change in the there distribution throughout the estuary.  These were with the abundances given the Diatoms Thalassiosira rotula (1875), Chaetoceros spp. (1445) and the Dinoflagellate Karenia mikimotoi (750).  Downstream of the King Harry Ferry there were four species present that were not found upstream, these were with the abundances given the Ciliate Mesodinium rubrum (50), the Diatom Rhilzosolenia alata (20), the Dinoflagellates Alexandrium spp. (5) & Protoperidium spp (25) and a Silica-flagellate. The species only found upstream of the King Harry Ferry were the Diatoms Eucampia spp. (5) & a Centric Diatom (5), as well as the Dinoflagellate Ceratium fusus (5).  These were all in very low concentrations which could explain their absence from the upstream/downstream sample sites.  The remaining species are as follows with abundances given; the Diatoms Rhizosolenia stolterfothii (200), Rhilzosolenia delicatula (280), Rhizosolenia setigera (145), Nitzschia spp. (240) and Melosira spp. (20), the Dinoflagellate Prorocentrun micans (220) and an unidentified Ciliate (60).

Zooplankton Analysis

A zooplankton sample was taken just upstream of King Harry Ferry during the RIBs estuarine work. The total number of zooplankton organisms found at this site was approximately 200 organisms/m^3. The most abundant species group was copepoda with ~71 specimens/m3 followed by cirripedia larvae (barnacles.) with a level of ~61 specimens/m3 . The abundance of barnacles could possibly be explained by the proximity of the station to the mussel fishery. The mussel fishery provides an ideal environment for species such as barnacles and limpets, which would also explain the presence of Littorina Eggs in the sample. This appears to be an area of relatively low zooplankton species abundance and diversity (with only 9 different species within our sample).

In addition to this, two zooplankton samples were taken from the R/V Bill Conway on 15/07/06. One was taken upstream of the King Harry Ferry (a very similar location to the RIBS sample) and the other was taken from the mouth of the estuary. The first shows the same level of diversity as the RIBS sample and a very similar abundance with 234 organisms/m^3. The second shows both greater diversity (12 species groups) and greater abundance (317 organisms/m^3) The dominant species in the first sample was Cirripedia Larvae (barnacles) as was found in the RIBS sample. This is in contrast to the estuary mouth sample which shows co-dominance between Copepoda and Hydromedusae. The increase in zooplankton abundance and diversity can be related to water column light levels. The secchi depth measurements taken during the survey show that the light levels increased downstream due to decreasing suspended particulate matter concentrations. This results in a greater level of phytoplankton downstream and therefore greater levels of zooplankton.

Chlorophyll Analysis

The results appear to show that there is no chlorophyll maximum present in the estuary. However at station 2 a relative chlorophyll peak of 6.4 ug/l is apparent at 4m depth. With the exception of stations 2, 3 and 5 there is no decease of chlorophyll with depth. At stations 2 and 3 this may be accounted for by the presence of a local shellfish farm. Surface chlorophyll samples range from less than 1 ug/l to ~10ug/l. chlorophyll concentrations show a general trend of decreasing values with distance from the freshwater influence. See figure 1.
 

ADCP and CTD analysis

The first transect taken at the upper reaches of the estuary shows the faster moving (~0.125 m/s) layer of water on the bottom. This is assumed to be sea water penetrating north up the estuary, as sea water is colder and more saline than river water; therefore forming a denser lower layer.  This is overlain by a slower moving (~0.05 m/s) layer, assumed to be river water. The CTD data show a large change in salinity with depth indicating that there are indeed two bodies of water overlaying each other. See figures 2 & 3.

fig(2) Salinity vs Depth	fig(3) Velocity vs Depth
Click diagrams to enlarge

The transect taken across the mouth of the estuary shows very little or no movement of water over the channel and eastern side of the estuary. The backscatter contour plot shows very high surface backscatter (surface roughness) and decreasing backscatter with depth. This indicates that the seawater was underlying the river water; river water results in higher backscatter as it contains higher sediment and particulate load. On the east side there is faster (~0.5 m/s), north-easterly moving, water that may be a result of mixing between southerly-flowing surface river water and northerly-flooding seawater. The underlying layer of presumed seawater has a more northerly direction as it undercuts the river water. The transect was taken near the end of flood tide resulting in the low maximum velocity at the mouth of the estuary.  See figures 4 & 5.
 

fig (4) Velocity Magnitude	fig (5) Velocity Direction
Click diagrams to enlarge

Again, the transect across Falmouth harbour shows faster, westerly-moving bottom water presumed to be the penetrating seawater with an overlying layer of slower, north-easterly moving water. This is presumed to be the river water flowing into the estuary. The CTD data confirms that the top layer is warmer and less saline and that the bottom layer is colder and more saline. See figures 6, 7 & 8.

fig (6) Salinity vs Depth	fig (7) Velocity Magnitude	fig (8) Velocity Direction
Click diagrams to enlarge

Oxygen Concentration Analysis

On collection of water samples on the boat, the concentration of dissolved oxygen was fixed using 1ml each of Manganese Chloride and Alkaline Iodide. The glass bottles were stored under water to maintain air tight conditions until the time of lab analysis.

Lab analysis involved the addition of 1ml of sulphuric acid to each sample and thiosulphate titration.

5 standards were produced using 10ml of Potassium Iodite, 1ml of Alkaline Iodide and 1ml of Sulphuric Acid. These bottles were topped up using MilliQ Water and also titrated using the Winkler method. The results are shown in figure 9.

The data collected for oxygen saturation showed no significant patterns.  This indicates that an increased number of samples may be required to build up a more continuous profile of the oxygen saturation.  However, this would have been more time consuming and a YSI probe could be used to give an unbroken profile of oxygen saturation.

Nitrate Analysis

The concentration of nitrate in the water samples was analysed using a spectrophotometer and a flow injection system. A peristaltic pump feeds the flow of 1% sulphanilimide, 0.1% Naphthyl ethylene-diamine dihydrochloride and a carrier solution. The water samples were injected into the system. The reagents caused a reduction from nitrate to nitrite on passing through a catalyst of copperised cadmium. This allowed the spectrophotometer to perform the colourimetric analysis by measuring the absorbance of light by each sample. The absorbance differs with the strength of colour of the sample which in turn is affected by the concentration of nitrate. The value obtained is a concentration of nitrate plus nitrite. However, it can be taken as a value for nitrate because nitrite accounts for only a small proportion. The absorbance readings were traced by a plotter to give peaks for the standards and each sample. The standards were used to plot a calibration curve and the concentration of nitrate in each sample derived from this.  The results are shown in figure 10.

The points plotted on the nitrate estuarine mixing diagram are close to the theoretical dilution line. Therefore, nitrate appears to be behaving conservatively. This is the opposite of what we expected to see given the time of year; the chlorophyll data collected at the same time indicates that there are high levels of primary production occurring. It is possible that the input of nitrate is being matched by the biological removal due to low summer riverine input. Therefore, non conservative behaviour is most likely, with the apparent conservative behaviour being caused by a balance between input and removal. This notion is supported by the situation of some points slightly below the theoretical dilution line.

Phosphate Analysis

To calculate phosphate concentration, the following steps were made: prepare working standard solution; stock solution was diluted using MQ water:

prepare calibration and 3 blank solutions

prepare samples and 5 random replicates

add mixed reagent to blank, standard and sample solutions.

A photospectrometer was used to determine the concentration of each standard, which could then be plotted against absorbance of light to produce a calibration curve (see figure 12). From this, it is clear to see that an increase in phosphate concentration corresponds to an increase in the absorbance of light measured by the photospectrometer.

The concentration of each water sample can then be determined from the calibration curve.

 

Fig (12) Click diagram to enlarge

The estuarine mixing diagram shows that phosphate behaves non-conservatively within the Fal estuary. It appears to be removed throughout the majority of the estuary. However, the water sample collected at the site nearby the fish farm was found to be higher in phosphate than the rest of the estuary. This is to be expected as excess nutrients are added to the water in order to enhance growth of the shellfish being farmed.
 

Silicon analysis

From the data sampled on 8th July 2006 the Silicon Concentration (µmol/l) ranged from 0.79 to 27.98 µmol/l and showed apparent non-conservative behaviour at this time of year. This means that the fresh water end member was much further up stream than we could sample, because of the low riverine input. However, FW end member samples were taken on 6th July on the River Truro and were found to be 81.2 µmol/l. There were peaks at 27.19 and 27.98 µmol/L; this was taken at the Fish Farm (mussels). Souchu et al (2001) suggested that an area with increased shellfish biomass may exhibit a relative decrease in phytoplankton biomass, which could induce a decrease in nutrient demand. Thus an increase in the Si concentration observed around the fish farm. See figure 13.

Locations involved for RIBs

Vertical Profile of the Physical Characteristic of the Fal Estuary

The vertical profile of temperature and salinity shown in figure 14 represents the physical structure of the estuarine water column. The temperature decreases slightly with depth. This is because river water (which is warmer than sea water at this time of year) is flowing over the surface. Solar irradiance also causes surface water to be warmer than deeper water. Salinity is seen to increase with depth, as the sea water is flowing into the estuary along the bed. The water column is therefore observed to be statically stable. The ADCP data collected during the estuarine survey supports the notion of a typical two layer estuarine

circulation with a landward flow at depth and a seaward flow at the surface. However, the low summer riverine discharge means that the estuary is tidally dominated in terms of flow. Therefore, the tide is penetrating further up the estuary than perhaps it normally would. This evidence suggests that perhaps the Fal estuary is partially mixed. The temperature and salinity changes are very small, which indicates a well mixed estuary. Conversely, a secondary circulation can not be supported by a well mixed estuary and hence the suggestion of a partially mixed estuary. More study is required at different times of year and states of tide in order to gain a fuller impression of the Fal estuary’s physical characteristics. The dissolved oxygen plot also shown in figure 14 shows a subsurface maximum and a gradual decrease with depth. This is likely to be due to a subsurface photosynthesis maximum, which often occurs as a result of photoinhibition at the surface and light limitation at depth.

Offshore Chemical and Biological Analysis

The offshore survey carried out on R/V Callista on the 8th of July 2006 aimed to investigate the vertical structure of the water column in terms of physical, chemical and biological parameters. The survey was carried out as a time series of observations whilst at anchor approximately 10miles south-east of Falmouth estuary. ADCP data and CTD data was used to draw conclusions about the structure of the water column and to determine sampling depths along the vertical CTD profiles. A vertical plankton net was also used to sample the zooplankton and analysis of the plankton and chemistry was carried out in the lab the next day.

Callista Biology Data Analysis

Samples were taken at hourly intervals from 10:30 GMT as part of a time series profile at approximately Lat 50°00.063 & Long 004°50.262. For phytoplankton, samples were taken at two intermediate depths depending on the position of the thermocline. Samples were then stored in lughols iodide and labelled. In the lab samples were decanted to 100ml and from this 10ml taken; a further 1ml was then viewed under the microscope to allow identification of the different phytoplankton species. In total twelve samples were taken from three cast but we were unable to do anymore as the cable was damaged on the third cast. These gave deeper depths of 24.1, 22.0 & 17.9m and shallower depths of 13.0, 11.0 & 17.3m.

3 groups / orders were identified and Dinoflagellates were found to be more abundant than Diatoms or Ciliates. However, Diatoms showed a greater diversity (12 species) than Dinoflagellates (5 species) and Ciliates (1 species). The reason for this was because of the presence of the Dinoflagellate Karenia mikimotoi (shown in the image to the left), which was the dominant species at both depths. In total there were 4015 organisms identified and of this 3275 were K.mikimotoi. However, there were differences between the deeper and shallower sampling depths.

The deeper depth had a lower diversity (9) and a lower abundance (1095) than the shallower depth (diversity = 10 & abundance = 2920). In terms of group/order diversity, the deeper depth had 5 Diatoms, 3 Dinoflagellates and 1 Ciliate. The reason for this was again because of the presence Karenia mikimotoi, which was the dominant species. At both depths it was in roughly the same proportion of 80% of the total population. Although most species were present at both depths, there was an increase in abundance for all species at the shallower depth. The shallower depth had 3 Diatoms (Guinardia flaccida, Heptocylindrus spp & Rhilzosolenia delicatula) and 1 Dinoflagellate (Gyrodium spp.) that were only present at this depth. The deeper depth had 1 Diatom (Rhilzosolenia alata) and 2 Dinoflagellates (Prorocentrun micans & Protoperidium spp), that were only present at that depth. Protoperidium spp is also a rare species for this area. The following species were found at both depths; Diatoms Rhizosolenia setigera, Thalassiosira rotula, Rhizosolenia stolterfothi, an unidentified Centric Diatom, the Dinoflagellate Karenia mikimotoi and an unidentified Ciliate.

Zooplankton samples were taken using a plankton net with a diameter of 50cm and mesh size of 200µm. Three vertical tows were taken and the details of each are shown below:

The bottle volume sampled was 500 ml and from this the water sampled for each site is as follows; P1 gave 1.37 m3, P2 gave 3.9 m3 and P3 gave 2.94 m3. Then 5ml was taken as an aliquot size for microscope analysis. P1 had heavy layback induced by a strong tidal flow that resulted in the volume of water sampled being greater than calculated. Hence there was a larger abundance of organisms for P1 (30145), compared with 5232 and 5850 for P2 and P3 respectively. In total there were 41227 organisms from 15 groups / orders identified, with 9 groups / orders being present on all samples. They were (in order of abundance); Copepoda (19369) , Hydromedusae (Jellies) (7182), Chaetognatha (5293), Copepoda nauplii (2403), Decapoda larvae (Crabs/Shrimp) (1804), Appendicularia (Larvacea) (1052), Siphonophorae (989), Cladocera (582) & Polychaeta larvae (371).

P1 had all the groups / orders identified in its sample. Both P2 and P3 were lacking Cirripedia larvae (Barnacles). However, P2 was also lacking Gastropod larvae, Mysidacea and Ctenophora, where as P3 did not have either Echinoderm larvae or Fish Larvae. The total abundances for these groups / orders were as follows; Cirripedia larvae (Barnacles) (876), Gastropod larvae (472), Mysidacea (311), Ctenophora (248), Echinoderm larvae (176) and Fish Larvae (99).

In conclusion the most abundant form of zooplankton was Copepoda (shown in the image above) with 19369 organisms identified and there was little change in the diversity of the samples during the course of the day. However, for phytoplankton there was a more obvious change in diversity above and below the thermocline but this was not as important and 80% of all the phytoplankton sampled at both depths was Karenia mikimotoi.

Callista Chlorophyll Analysis

Chlorophyll is a good indicator of phytoplankton biomass. Chlorophyll maxima are present for all samples on the time series. They occur at similar depths of ~ 11-17m. The first sample taken at 10:30 GMT shows a chlorophyll maximum of 5.4 μg/l at a depth of 17.3m. The sample later in the day at 11:42 GMT had a shallower chlorophyll peak of 6.6 μg/l at a depth of ~11m. The final sample taken at 1253 GMT showed a chlorophyll maximum of 3.9 μg/l at ~17m depth. The samples were taken (Niskin bottles) on an up-cast of the CTD after analysing the fluorometer data for chlorophyll peaks. This method produced somewhat engineered results but was necessary due to the limited number of sample bottles. Chlorophyll values at depth show similar results to the surface samples (<1 μg/l) where photo-inhibition is probably the cause of the relatively lower results. At depth there is not enough light to support a higher biomass of phytoplankton.  See figure 15.

Callista ADCP and CTD Analysis

ADCP velocity data collected over the sampled time series clearly shows a layer of water with decreased speed (~ 25m/s slower) at approximately 22m depth (ADCP1); corresponding with the base depth of the thermocline. Although no physical explanation for this reduced velocity has been proven, it may be that the very steep thermocline in this area causes acoustic refraction of the ADCP pulse. Therefore this layer may not in fact be a real phenomenon but an artefact of the ADCP itself.
Backscatter data from the time series show two defined peaks in backscatter at 8m and 28m, indicating that there were two areas of high zooplankton density (ADCP 2). Data from the CTD profiles consistently revealed two chlorophyll maxima at depths of 12m and 25m (CTD 1). The similarity between zooplankton and phytoplankton peaks is typical of the documented predator prey relationship expected between these two groups of plankton. The two peaks indicate a structure of two phytoplankton communities; a surface community which is likely to be nutrient limited and a thermocline community which is likely to be light limited.  See figures 16, 17 & 18.

fig (16) Flourometry against Temperature and salinity	fig (17) Average speed against depth	fig (18) Average backscatter against depth
Click to enlarge

Callista Oxygen Analysis

The oxygen content at surface can be seen to increase throughout the day with a value of 97.6% at 10:30 GMT rising to a value of 118.9% at 12:53 GMT. This may be due to the increased activity at the sea surface, leading to greater oxygen diffusion across the air-sea interface. The chlorophyll maximum of greater magnitude is apparent at ~10-13m depth with the greatest values of oxygen saturation seen (~123%). A second but smaller chlorophyll peak observed on the fluorometer correlates with the relative oxygen levels observed from the lab analysis at ~21-24m depth. An overall decrease of oxygen from the surface to depth can be seen, with the exception of the 11:42 (GMT) profile. In the case of this profile oxygen levels are seen to be at saturation levels close to that of the chlorophyll maximum (~118%). The second and third time series appear to be similar in structure, however the initial readings are somewhat different, this may be due to the ebbing tide (high tide at 0559 and 1253) bringing different water masses.  See figure 19.

Callista Nitrate Analysis

Cast 1 had a surface concentration 0.4 µmol/L, this then increased to a peak of 2.3µmol/L by 17.3m, which was just above the thermocline. There was then a decrease in concentration by 0.6 µmol/L below the thermocline at 24.5m and it then fell further to 0.7µmol/L by 68m. Cast 2 had a higher surface concentration than Cast 1, which was 2.0µmol/L. This then fell to 0.8 µmol/L by 11m, however, the concentration then peaked at 2.3 µmol/L by 22.0m. From here the concentration then fell to 0.7 µmol/L by 65.8m.

At the surface, Cast 3 was similar to Cast 1 because it had a concentration of 1.0 µmol/L and rose to 2.8 µmol/L by 13m. The concentration then fell to 0.8 µmol/L by 17.9m but unlike Cast 1 the concentration then increased to 3.0 µmol/L by 66.2m. It is difficult to interpret this data because each cast had different behaviour. However, it could be viewed as the daily change in the tidal cycle.  See figure 20.
 

Callista Phosphate Analysis

This time series depth profile shows high surface phosphate concentrations, with a marked decrease in concentrations between 11m and 17 m for all three CTD casts. This is as expected and is likely to be a result of high phytoplankton densities in this depth range which is indicated as a chlorophyll maximum by the chlorophyll data. This is then followed by an increase in phosphate concentrations at about 20m corresponding with a rapid decrease in chlorophyll. In rofiles 1 and 2 the concentrations gradually decrease with depth (0.0011mmol/l/m2 ) down to the maximum depths. However, in profile 3 there was a large increase with depth in phosphate concentration (0.0053 mmol/l/m2 ). This also relates to the chlorophyll time series profile, in that profile 3 at 12:53 GMT decreases much more rapidly with depth, so that phosphate concentration increases.  As shown in figure 22, with the calibration curve (figure 21) in the figures below:

fig (21)	fig (22)

Callista Silicon Analysis

Surface levels for silicon are of similar values for all time series (~4.3 µmol/l). For the two later time series, no significant change in Silicon concentration with depth was observed until the chlorophyll maximum. However, in the first time series at 10:30 GMT the corresponding silicon value reached 17.3 µmol/l. This appears to be an anomalous result. From ~10 m to 20m there was a marked decrease in the levels of silicon in all three of the time series. This was assumed to be the product of high primary production from phytoplankton present at this point in the pelagic region. Below the depth of the second chlorophyll maximum there is minimal change in the silicon value. The final samples at depth drop to a level of ~2 µmol/l.  See figure 23.

General Conclusions

Geophysics Conclusions

Estuarine and RIBs

The estuarine study indicated that diatoms were the dominant phytoplankton group throughout the estuary. Zooplankton populations, however, displayed a transition from largely copepod dominated at the head to co-dominance between copepod and hydromedusae at the mouth of the estuary. Chlorophyll concentrations appeared to be consistent with depth although there was a lateral decrease approaching the mouth of the estuary. Oxygen concentrations displayed no significant trends.
Nitrates display conservative behaviour throughout the estuary with phosphate and silicon behaving non-conservatively with addition of these nutrients at the mussel farm.
ADCP and CTD data generally show saltwater intrusion with the overlying river water. There is significant surface mixing between these two water types at the mouth of the estuary.

Offshore Conclusions

Results from the biology analysis found that the phytoplankton community is dominated by Karenia mikimotoi and that the zooplankton community is dominated by Copepoda. Chlorophyll maxima were found between 11 and 17m deep and the highest concentration was 6.6µg/l. Oxygen concentrations at the surface increased throughout the day from 97.6% to 118% saturation. The highest value overall was at the chlorophyll maxima which was 123%. Below the chlorophyll maxima, the oxygen concentration decreased with depth. No clear conclusions could be drawn from the Nitrate data because each cast had different behaviour. However, it could be viewed as the daily change in the tidal cycle. Low phosphate concentrations were found in the region of the chlorophyll maxima. This is a result of biological uptake by photosynthetic organisms. All Silicon levels decreased below the chlorophyll maximum. Cast one appears to show an anomaly as there was a drastic increase by approximately 13µmol/l at the chlorophyll maxima. The other casts showed no significant change in Silicon concentration above the chlorophyll maximum. Backscatter data from the ADCP and chlorophyll data from the CTD show corresponding peaks in phytoplankton and zooplankton. This indicates two communities; one near the surface and one at the thermocline.