Sampling Strategies:
For this section of our investigation, we split into 3 groups and collected samples using a combination of 2 methods.
Firstly, two vessels: The Falcon Spirit and Winnie the Pooh were used to record the spatial changes in the estuaries biological, chemical and physical properties.
The Falcon Spirit started at the mouth of the estuary, just before the breakwater at 8:36 UCT and then proceeded part way up the estuary, to Tamar bridge, and to return back down the other tide finishing at 13:50 UTC. Samples were taking at 9 stations starting at H and ending at J. At each station the CTD was lowered recording, temperature salinity, fluorescence, turbidity and oxygen. In addition, Niskin bottles were closed at decided depths to collect direct measurements of phosphate, silicon, oxygen, phytoplankton and chlorophyll. At stations H, E and J five-minute zooplankton trawls were also conducted.
Winnie the Pooh progressed from the Tamar bridge upstream to Calshot, in a cruise that took place from 10:00 to 13:00. Samples were taken moving North in order to reach the most Northerly point possibly, as high tide was at 14:04 UTC. The aim of this expedition was to have a more complete data set of chemical and biological parameters, continuous with the lower estuary data set. Salinity and temperature readings were taken at surface levels at 18 sites moving upstream, at the same time as nutrient samples (using a single Niskin bottle) and periodic phytoplankton samples (preserved in Lugol’s iodine). At the start, middle and end of the transect a zooplankton horizontal net collection was made, the first of these being five minutes in duration, the next three and the last one, due to increasing levels of organic matter in the water.
Secondly, a time series was conducted on the Saltash town pontoon located just north of the 1854 I.K Brunel Railway overpass bridge. The pontoon lies approximately 6 miles North of the Plymouth breakwater, where as a result of a 4.7m tide, occurring at 13:58 UTC, was subject to large variations in physio-chemical conditions. Sampling for a 7-hour period allowed the analysis of changes in temperature, salinity, nutrients and flow velocity over a large section of the tidal rage. The Saltash pontoon was used to construct a time series of temporal changes over time in a fixed location, to act in compliment to the spatial changes recorded by the Falcon Spirit and the Winnie the Pooh. Measurements were taken from the edge of the Saltash pontoon every 30 minutes in order to produce a time series demonstrating changing physical and chemical conditions as the tide turned to the flood. The T/S probe was used to record depth (m), temperature (oC), oxygen saturation (%), oxygen concentration (mg l-1), salinity, turbidity and chlorophyll concentration (µg l-1). Light attenuation and river flow speeds were recorded using a light sensor and current meter respectively. In order to measure the nutrient concentrations, a Niskin bottle collected samples from the surface and bottom depth of the river which were then filtered and placed in acetone.
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