Conclusion

Conclusion

Over the past two weeks, we have systematically surveyed the Fal Estuary and surrounding area to provide an accurate scientific picture of the chemical, biological, oceanographic and geophysical properties of the rivers, estuary and offshore. A large range of vessels and equipment were used to collect the necessary data for our studies. The data set finally collected in one of the largest for a research programme of this nature.

This was the 1^st time Falmouth was studied by the National Oceanography Centre students, meaning that the findings were extremely important to provide a basis for future projects and investigations. Below is the final summary of our investigation, presenting the major conclusions drawn from the data collected.

RIBS

The data collected from the rivers showed that nutrient concentrations are extremely high in this area, resulting in eutrophic conditions. Nitrate especially was unusually high, although this was expected due to the Nitrate Sensitive nature of the estuary. This triggered large phytoplankton blooms, reflected in the chlorophyll data collected. The phytoplankton samples were found to contain different species upstream in the river than they did downstream. Upstream, the population was found to be over 80% dominated by one species in particular; Nitzschia sp. whereas further downstream the population is more diverse, reflecting the different organism’s tolerance to changing salinities.

Physically, the estuary was tidally dominated all the way to the upper reaches, with salinity readings changing rapidly over a very short distance in time. There is evidence of a salt wedge at the very top of the river; however increased tidal strength downstream means that better well mixed conditions prevail further down the estuary.

R.V. Conway

Within the estuary itself, results collected aboard the Bill Conway have shown that like the RIBS, the estuary was highly eutropic, stimulating unusually high phytoplankton blooms unique to this area.

Overall nutrient analysis recorded conservative behaviour down the estuary for nitrate and silicate, although there was slight non conservative addition of phosphate at higher salinities (beyond 34.2 salinity units).

CTD results recorded very little salinity and temperature changes with distance downstream, illustrating well mixed behavior within the water column. Analysis of stability and current shear using Richardson numbers found that more stable conditions prevailed near the head of the estuary, where advective mixing processes dominated. In contrast, further downstream increased instability meant that conditions became more turbulent, and that vertical mixing was more apparent.

R.V. Callista

Our aim aboard the Callista was to analyse the front found seawards from the estuary. It was concluded that the estuary side of the front was more mixed with high nutrient surface waters but low chlorophyll surface waters. These low chlorophyll concentrations are due to high vertical mixing, therefore causing the phytoplankton to be moved downwards into the deeper waters where there is insufficient light for photosynthesis to occur.

However, over the seawards side of the front, the water column was found to be far more stratified because of the depth of the water. This caused the water to have a small nutrient content in the surface waters, restricting the phytoplankton bloom to deeper down, just above the thermocline. Growth here is therefore nutrient limiting.

At the front itself, conditions were at an optimum between these two extremes, hence why higher chlorophyll concentrations were found.

Another discovery, one which was not to be expected, was made further offshore. Here, measurements off the ADCP found an area of reduced current flow, which is still currently been unexplained. Possible outcomes are gearing towards enhanced refraction of the sound wave emitted from the ADCP instrument, or possibly the presence of enhanced internal wave breaking. Research into this phenomenon continues today.

To conclude overall, studying Falmouth estuary has provided us with a number of findings unique to only this estuary and no other. It represents an exciting area of scientific research which must continue if we are to truly understand the behavior of this highly dynamic system.

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