Home Estuary Pontoon Offshore Habitat Mapping

The Fal Estuary is situated on the South coast of Cornwall, UK (See Map). It is a ria system comprised of two main regions, the inner tidal tributaries and outer tidal basin (Pirrie et al., 2003). The outer tidal basin is known as the Carrick Roads and contains 80% of water volume in the Fal Estuary (Hughes, 1999). The inner tidal tributaries contain creeks and tidal rivers reaching 17km inland (Tappin et al., 2010), which the Fal Estuary is fed by the Carnon River via Restronguet Creek (Somerfield et al., 1994).


Historical records show the catchment areas of the Fal Estuary have a long history of extensive mining, hence a sediment metal concentrations gradient can be found along the Fal Estuary (Warwick, 2001). However this estuarine system can neither be treated as pollution nor recovery events as it was discovered that some populations in the system have developed metal tolerance with physiological modifications (Langston et al., 2003).


In 1992, Restronguet Creek was contaminated by a mine incident (Wheal Jane mine) (Pirrie et al., 1997). Along the estuary from Restronguet Creek, dredging performed at Falmouth dock and harbour areas were found to contain high levels of toxic substances from antifouling paints including polychlorinated biphenyls (PCBs) and tributyl tin (TBT) (Matthiessen and Law, 2002).


The factor of human activities (commercial and recreational) has always been the major influence on both the quality of the Fal Estuary and economy of west Cornwall over time (Cornwall County Council, 2006).  In 2006, Fal & Helford Special Area of Conservation (SAC) was established to achieve the balance between the two (Cornwall County Council, 2006).


The aim of this field course is to produce an overview of the chemical, physical, geological and biological aspects in the Fal Estuary. We are interested in the current state of the Fal Estuary.  In order to achieve our aim, surveys and water analysis along the Fal Estuary are conducted from the 25th June to 2nd July; from King Harry pontoon (water column analysis) to St Mawes harbour (habitat mapping) to offshore area (time series at one location).


Estuary

Sampling up the Fal estuary a survey was conducted which took secchi disc measurements, CTD water samples and ADCP horizontal transects. Samples were taken across 7 different stations, from offshore to the river end. Temperature, salinity, fluorescence, transmission, velocity magnitude, backscatter, nutrients, phytoplankton and zooplankton were taken at each station. From the data collected, flushing time, residence time, Richardson number and light attenuation coefficients were calculated. Charts, graphs and mixing diagrams were compiled using the data and calculated values. From the results, it was found that the estuary seemed to have a well-mixed structure offshore and became more stratified towards the river end, however the Ri number graphs seem to slightly contradict the depth profiles taken with the CTD as the Ri number suggest that, at certain stations, parts of the water column are stratified, when the depth profiles suggest they were well-mixed. There were no definite conclusions made concerning the behaviour of nutrients in the estuary, this was difficult because the data only consisted of salinities 29-35. Although, using incomplete mixing diagrams, predictions were able to be made for the behaviour of each nutrient, silicon showing conservative tendencies similar to nitrate whereas phosphate was non-conservative. However as eluded to these diagrams were not conclusive. Patterns were also found between light attenuation and turbidity, as turbidity increased up the estuary, light attenuation decreased.


Pontoon

The King Harry Ferry Pontoon is located in the Fal River on the South Coast of Cornwall. Using the pontoon, the physiological parameters of the water column were studied as the tide ebbed, decreasing the depth of the water column, and changing its features. It was noted that all factors observed changed with the tide, and suggested- that with the data gathered- the water column at the King Harry Ferry Pontoon is dominated by coastal flux.


Offshore

A time series was carried out off the coast of Falmouth over an 8 hour period. Using a CTD, ADCP and chemical analysis, the physiological and organic properties of the water column were studied. A thermocline was a clear feature of the water column, and a high Richardson number around such a thermocline further proved the water column was heavily stratified. Nutrients were found in greater abundance around the thermocline, and coupled with that, a higher level of fluorescence, and thus phytoplankton. To act upon the large levels of phytoplankton, a wide diversity of Zooplankton orders were found below the thermocline.


Habitat Mapping

Using a Sidescan Sonar, a habitat map of St. Mawes Harbour (Falmouth, Cornwal) was created. The map was then studied and utilising video transects of the area, the distinct areas on the sidescan were identified and assigned. What could be seen was the kelp, seagrass (eelgrass) and seaweed dominated the environment where there was epifauna, though some spaces had little epifauna, instead suggested a wealth of infauna. Pylaiella littoralis, a fast growing filamentous macroalgae, which is potentially a danger to many rarer algal species was also present.


References

Cornwall County Council, (2006). Fal and Helford Marine Special Area of Conservation Management Scheme. Truro: Fal & Helford Special Area of Conservation (SAC) Management Forum.

Hughes, S. H. (1999). The geochemical and mineralogical record of the impact of historical mining within estuarine sediments from the upper reaches of the Fal Estuary, Cornwall, UK. Fluvial Sedimentology VI:(Special Publication 28 of the IAS)28 161 pp.

Pirrie, D., Camm, G. S., Sear, L. G., & Hughes, S. H. (1997). Mineralogical and geochemical signature of mine waste contamination, Tresillian River, Fal Estuary, Cornwall, UK. Environmental Geology29(1-2), 58 – 65 pp.

Pirrie, D., Power, M. R., Rollinson, G., Camm, G. S., Hughes, S. H., Butcher, A. R., & Hughes, P. (2003). The spatial distribution and source of arsenic, copper, tin and zinc within the surface sediments of the Fal Estuary, Cornwall, UK. Sedimentology50(3), 579 – 595 pp.

Tappin, A. D., Barriada, J. L., Braungardt, C. B., Evans, E. H., Patey, M. D., & Achterberg, E. P. (2010). Dissolved silver in European estuarine and coastal waters. Water research44(14), 4204 - 4216 pp.

Langston, W.J., Chesman, B.S., Burt, G.R., Hawkins, S.J., Readman, J. and Worsfold, P. (2003) Characterisation of the South West European Marine Sites. The Fal and Helford cSAC. Occasional Publications. Marine Biological Association of the United Kingdom 8 160 pp.

Matthiessen, P., & Law, R. J. (2002). Contaminants and their effects on estuarine and coastal organisms in the United Kingdom in the late twentieth century. Environmental Pollution120(3), 739 – 757 pp.

Somerfield, P. J., Gee, J. M., & Warwick, R. M. (1994). Soft sediment meiofaunal community structure in relation to a long-term heavy metal gradient in the Fal estuary system. Marine ecology progress series. Oldendorf105(1), 79 – 88 pp.

Warwick, R. M. (2001). Evidence for the effects of metal contamination on the intertidal macrobenthic assemblages of the Fal Estuary. Marine Pollution Bulletin42(2), 145 – 148 pp.


The Team

We are a group of 10 students from the University of Southampton. We consist of a mixture of Marine Biology and Oceanography undergraduates, allowing us to combine different skill sets and approaches to our investigations.


Jenny Bortoluzzi - BSc MB w/ OC

Callum Brown - MSci MB

Bede Ffinian Rowe Davies -  MSci MB

Rebecca Dowle - BSc OC

Samantha Hewkin - MSci MB

Louise King - MSci MB

Cheuk Ying Lau - MSci MB

Ben Seath - BSc OC

Georgie Tuffin - MSci OC

James Wrycraft - BSc MB


The Fal Estuary

Disclaimer- the views shown here are solely of group 10 and do not necessarily reflect the views or opinions of the university of Southampton.