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Falmouth Group 9 2015 Summary

Chemical Summary

Oxygen data from the estuary varied significantly when comparing datasets taken from the CTD and those worked out from water samples in the lab. The CTD shows the estuarine water was supersaturated and the niskin bottles show that it was under-saturated. Dissolved oxygen (% saturation) decreases with depth and increase as the estuary progresses towards the sea. An area of depletion occurs between central stations due to possible biological and physical factors. NO3 concentration decreases along the estuary with the highest readings found at the most northern (Station 66). The nitrate source is terrestrial based and enters the estuary during periods of precipitation. The mixing diagram shows non-conservative behaviour with removal at high salinities with the estuary acting as a sink in summer months. Within the water column chemical processes e.g. denitrification, takes place, stripping the nitrate from the water column. Phosphate concentration decreases as salinity increases. The addition of phosphate to the water column could be explained by the leaching of agricultural fertilisers into the river, inputs from local sewage plants or drainage from old mines. Silica concentration is high and the TDL shows addition of silica to the water column. Silicon enters estuaries by lithogenic input. This is not the expected outcome as diatom numbers are high and these primary producers remove silica from the sea water. The chlorophyll concentrations has presented to have no trend with salinity. The highest chlorophyll concentration was found at the most northerly station sampled (high freshwater influence) indicating the presence of phytoplankton, although they are unevenly distributed along stations.   


Physical Summary

The physical properties of the estuary seem to be dependent on the distance from the source, many of the features observed at the shallower more fresh part of the estuary begin to change predictably as we move into deeper, more saline water. The salinity, as expected, went from lowest at the station closest to the source (66) and gradually became more saline as the Bill Conway moved to stations closer to the estuary’s mouth. There was little change in salinity over depth possibly due to tidal mixing. This idea is supported by the analysis of the Richardson’s number which shows turbulent flow present at all stations. Turbidity was highest at Station 66 which was also the shallowest but some spikes in this data may as a result of the research vessel rather than any natural occurrence. Temperature responds to distance from the estuary source in an inverse was to the salinity, with the highest temperature at Station 66 and the highest at 70. However unlike the salinity, the temperature changes over depth (decreases) and as the estuary mouth is approached there is an indication to the development of a thermocline. Because of the strong tidal forces caused by the outgoing tide the total flux of the estuary has given a high value which may be higher than the actual flux however this is still a good indication. The estimate flushing time of the estuary is around 41.4 hours.


Biological Summary:

Chaetoceros sp is the most abundant species, present in Station 66-70 along with few other species. There are higher abundances in shallower depths. Copepods were found to be the most dominant group of zooplankton at Station 66 which had the greatest abundance of zooplankton. Cirripedia larvae and cladocerans were also found to be relatively abundant. It must be noted that the dominance by a few groups may be a result of sampling design.