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THE FAL ESTUARY SURVEY:

Discussion and Conclusions:

Chemical Discussion:

Nitrate removal is likely caused by phytoplankton uptake, but burial into the sediment and subsequent reduction to nitrite is another possible reason for nitrate values lower than dilution. (Christisen et al 1990) The fact that the Fal seems to exhibit nitrate loss is a good indicator of estuary health. Nitrate addition via terrestrial run-off of fertiliser is common in rivers worldwide, often to the detriment of the local environment.

Phosphate exhibits removal likely as a result of phytoplankton uptake. This is particularly significant in the case of phosphate because of treated sewage effluent. When sewage is treated, nitrate levels are controlled but phosphate levels are not. As a result you will often find higher phosphate levels as a result of sewage outflow. The removal of phosphate may therefore suggest that the Fal has low levels of sewage outflow. (Langston et al 2006)

Silicon behaviour is unclear. In the lower estuary silicon is removed, but towards the upper estuary it appears to be trending upwards. Silicon addition may be due to the chemical weathering of silicate rocks discharged into rivers. Silicon removal is likely due to uptake by diatom species for use in opal skeletons. Removal may also be caused by flocculation upstream where fresh water first meets the charged ions of salt water. Further samples are required for each nutrient (Si, NO3, PO4) closer to the river end members to see how these behave in lower salinity otherwise it is difficult to assume what the behaviour is.  

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Langston, W, Chesman, B, Burt, G, Taylor, M, Covey, R, Cunningham, N, Jonas, P, Hawkins, S (2006) ‘Characterisation of the European Marine Sites in the South West England: the Fal and Helford’, Springer, pp 321-333