Pontoon

Mixing and stratification in estuaries and coastal seas are controlled by numerous factors, one of which is freshwater input through mixing driven by tide and wind (16). The aim was to collect data and form a time series at the king harry pontoon. It was found that measured parameters all changed significantly throughout the period of measurement, which was during the ebbing tide. These changes would be primarily due to the changes in water column structure, such as the increase in the freshwater fraction or a decrease in depth as the tide recedes. This is shown in figure 7d where there is a decrease in surface salinity throughout the period, an indication of increasing surface freshwater and a reduction in saltwater concentration as a result of tides moving saltwater out of the estuary and rivers replacing it with freshwater which floats on top of the denser saltwater.

Offshore

Our off shore aim was to locate and observe the changes in a previously noted phytoplankton bloom. In order to achieve this we observed a number of different factors, primarily the levels of chlorophyll at different depths and locations. On top of this we looked at physical, biological and chemical changes throughout the water column, all of which are interlinked and known to affect one another. For example, temperature variations in the thermocline provide suitable conditions for phytoplankton growth, in turn forming a deep chlorophyll maxima. This growth thus has an effect on nutrient levels. This is supported by research at the L4 station in the western English Channel by authors(11) who show the intrinsic link between the physical, biological and chemical factors analysed in the results section.

Estuary

In the estuary our aim was to examine the effect of salinity on the properties of the water column and on nutrient profiles. We travelled up the estuary against the tide and took 5 samples en route. These samples suggested that overall temperature increased from the marine end of the estuary to the riverine end of the sample areas. An increase from approximately 15° to 19.9° over the course of the river. Ri number flow appeared to become more laminar as the boat moved further from the marine end of the estuary, where the marine area itself showed the most turbulent flow. In terms of biology, one species of phytoplankton dominated at all stations, Chaetoceros compressum was found in concentrations totalling 1046 cells/ml. Figure 5c shows consistence between phytoplankton abundance and nutrient data, suggesting the link between phytoplankton growth and nutrient availability. Zooplankton sampling returned a gradient of decreasing zooplankton numbers as sampling moved up the estuary, this was consistent with phytoplankton numbers, which provide a primary food source for zooplankton. Nutrient sampling up the Fal estuary returned similar patterns for silicon, phosphate and nitrate, all of which were found in relatively low concentrations between stations 61-64, whereas stations 65 consistently showed much greater levels. Station 65 was the shallowest of all the stations, these higher concentrations are likely due to riverine nutrient input making up a greater part of the water composition.

Habitat mapping

The aim of our habitat mapping was to identify the different habitat types across our transect and to analyse any change in structure due to the differing habitat types. This was completed by taking a sidescan profile of the transect and then taking both grab and video samples in order to identify the species abundance and species type at the different types of habitat. This was useful as it was found that the sidescan was supported by the video and grab. The main finding was that there was limited species variation and abundance at the sandy habitat type and there was a great increase in the rocky type. This is exhibited in figure 1 on the habitat mapping page which showed rocky habitat in the north and south of the transect but a sandy habitat in the central section. The limitation of sidescan is that it does not give a comprehensive view of the habitat type, hence why a video or grab sample is needed.

Phytoplankton - Biological results

Succession of phytoplankton impacts the species composition. Dinoflagellates can succeed diatoms in certain conditions, because they are motile, and at the point of the breakdown of the thermocline, this allows them a competitive advantage(12)(13). Dinoflagellates usually have a lower uptake capacity of nutrients to compete with diatoms when they are present (14)(15), but when nutrients begin to become limiting, diatoms start to sink out of the euphotic zone. Dinoflagellates use flagella and can respond to light(15). This allows them to remain in and access the small remaining photic zone, but also access nutrients below the nutricline. There is also evidence to suggest that dinoflagellates do better in warmer temperatures (6), so this may also be a factor in their succession. Silicate is usually the limiting nutrient for diatoms, as it is needed for their frustrule, which dinoflagellates do not have. These factors will be taken into account when further investigating the data collected.

SUMMARY

Nutrient levels in the oceans are changing(6). With changing nutrient levels, heavy metal inputs and physical properties, phytoplankton successions and assemblages change too, with possible eutrophication and other detrimental effects. Phytoplankton communities account for roughly half of global primary production, and have a huge impact of the biogeochemical cycling of many nutrients(7)(8). As producers, they are key in the transfer of energy through trophic levels(9)(10).

When the initial findings of group 7 are collaborated, the differences in properties examined can be explained by differing nutrient inputs and mixing processes, which are also influenced by succession of phytoplankton due to nutrient limitation.