Abstract

Surveys undertaken between 25th June 2013 and 1st July 2013 enabled enhanced understanding of the characteristics of the Fal estuary.

The geophysics habitat mapping project highlighted both anthropogenic and biological features, including presence of rocky shores, macroalgae and mearl. The pontoon study provided clear evidence of limited freshwater input, and dominance of tidal forces throughout with salinities ranging from 31.4 to 32.8. The estuary study gave enhanced understanding of the biogeochemical processes throughout the estuary with nitrate varying from 21μmol/l at the northerly point to 10μmol/l at Black Rock. Finally the offshore practical showed the differences in mixed and stratified water columns on and around frontal boundaries, and how these physical parameters affected the biological conditions with surface temperature ranging from 14.2oC in stratified waters to 12.4oC in mixed waters.

Through continuous sampling of the Black Rock station, both estuary and offshore profiles allowed a transect from riverine stations within the estuary to a station 16 nautical miles offshore to be sampled. This has shown clear changes in the phytoplankton and zooplankton community dynamics - with Chaetoceros clearly dominating within the estuary, whilst deep chlorophyll maxima being dominated with Nitzshia.  

Background

The Fal estuary is classed as a ria or a drowned river valley, it has formed as the result of sea level rise since the last ice age causing the flooding of the river system. This is the reason for its intricate tree-like morphology. It is also the third largest natural harbour in the world with a deep water channel known as Carrick Roads which extends 4 miles back from Black Rock to Turnaware Point (Pirrie et al). As well as these morphological characteristics, there are also significant biological and chemical processes that are influenced by its origins, such as the salinity gradient with respect to the horizontal direction. In these drowned river valleys, the size of the estuary is often disproportionate to the river size, since the river mouth has been totally engulfed by the saline water. This means fresh water influence is minimal relative to the sea, and as a result, especially high salinities are observed further up the river than would be expected.

The Fal estuary is of high ecological importance within the United Kingdom and is a Special Area of Conservation. The benthic environment within the estuary is ecologically rich, containing nationally important maerl beds comprised of two individual species, Phymatolithon calcareum and Lithothamnion corallioides., As well as extensive seagrass (Zostera) meadows. These species are habitat forming species and provide specific niches which support a high biodiversity.

Aim

The Aim of the Falmouth 2013 field course is to gain a detailed understanding of the Fal estuary and how the system works as a zone of transition between freshwater inputs and coastal waters. Understanding the Fal estuary will involve a series of surveys using the vessels and equipment provided by the University of Southampton, National Oceanography Centre and the Falmouth Marine School. These surveys include:

• A collaborative survey over an 11 day period by all 13 groups to provide a time series of physical data from the King Harry pontoon.
• An offshore survey aboard the R.V. Callista with the objective of discovering how vertical mixing processes in the water off Falmouth affect, directly and indirectly the structure and functional properties of plankton communities. This involves observing the physical, biological and chemical processes occurring.
• A survey of the Fal estuary aboard the R.V. Bill Conway to gather data on the biochemistry of the estuarine system with the intent to create estuarine mixing diagrams, and also the physical processes that are present.
• A geophysics survey aboard the MTS Viking, involving the use of a side-scan sonar fish, towed in transects along the maerl beds present along the shores of St. Mawes in the Fal estuary. The survey will provide data to produce a poster and habitat map of this site.

This website offers all information gathered by the observations and data collected on these surveys, along with the data collected from the post-survey biological and chemical laboratory analysis of collected samples. The site provides all details of the surveys days and also a collaborated analysis of the entire Fal estuary/offshore system as a singular entity. Group 3 as dedicated oceanography and marine biology students of the University of Southampton hope to provide a highly interesting and comprehensive study of the Fal estuary system with a special consideration to parameters such as; the physical structure of the Fal estuary from riverine to offshore, the effects of tides on the condition of the estuary over time, the nutrient environment of the estuary, the levels of algal biomass within the estuary and how they compare to offshore, the turbidity within the waters and their causes, comparison of light attenuation in estuarine and offshore waters, the controlling and limiting factors to primary production, and finally the observed planktonic communities and how they change from estuary to offshore.

Group3

Stephanie Britt – MSci Marine Biology

Lee Coley – MSci Oceanography

Eleanor Dening – BSc Oceanography

Christina Feilden – BSc Oceanography

Joseph Hudson – MSci Marine Biology

Ben Robinson – MSci Marine Biology

Victoria Sidwell – MSci Marine Biology

Christian Sitch – BSc Oceanography

Matt Townend – MSci Marine Biology

Mike Wilmot – MSci Oceanography

Fig. 1 A map of all the locations covered on the field course with respect to Falmouth.

Disclaimer: The opinions and conclusions expressed in this website are not affiliated with those of the National Oceanography Centre or the University of Southampton.

References
Pirrie D, Power M, Rollinson G, Hughes S, Camm G, and Watkins D, available at projects.exeter.ac.uk/geomincentre/estuary/home.htm