Falmouth Group 1

Headquarters: 50°09.287’N 005°04.386’W

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The Fal estuary was found to be predominately a well-mixed macrotidal estuary, with minimal levels of stratification in the upper estuary.  Moving offshore, the physical structure of the water column changed from the well-mixed estuarine conditions to a strongly stratified system with thermocline and halocline at approximately 25m depth. There was also a clear tidal front at the interchange between the two systems.

Nitrate and silicon showed conservative behaviour throughout the estuary due to the low residence time of 1 day 3 hours 3 minutes. However, phosphate showed significant addition in the lower estuary, most probably due to a variety of anthropogenic sources. Offshore, the nutrients generally showed characteristic depletion at the chlorophyll maxima, particularly in the more stratified water.

The phytoplankton community through most of the sampled area was dominated by diatoms, particularly Chaetoceros sp.. However, towards the upper estuary diatom numbers decreased with decreasing salinity but overall numbers of phytoplankton increased. The zooplankton was heavily dominated by copepods throughout the estuary and offshore and was usually situated underneath the phytoplankton peak. The estuary had a more larval-dominated zooplankton community, suggesting its role as an important nursery ground.

The small area of benthic habitat sampled showed a significant difference between the habitats within the main channel of the estuary and the surrounding shallower regions with less algae and more exposed sediment.

Authors

Chavasse, A.G., Fierens, L.M.L., Frankish, C.K., Lamp, K.R., Nixon, J.E., Owens, B.R., Schumacher, E.R., Truell, M.T., Wilson, R.W.