Introduction
On the 6th of July
2017 at 08:15 UTC, the Bill Conway was taken into the Fal estuary
with the aim of investigating the distribution of nutrients in relation to the physical
and biological characteristics of the area. The cloud cover varied from 3/8 to 0/8
and sea state varied from 1 to 0 on the Beaufort Scale. The survey, which began at
Black Rock and continued up the estuary towards King Harry pontoon, sampled four
locations and included multiple spatial and temporal transects at and
between stations
(recorded with an ADCP). Once at The King Harry pontoon, we moved from the research
vessel Conway onto the RV Winnie the Pooh. The RV Winne the Pooh travelled from the
King Harry Pontoon (at 12:00 UTC), up to Truro (at 14:22 UTC), and sampled 4 Stations
(1 station downstream of the lock and 3 upstream of the lock).
Method and Equipment
Conway
-
At each site temperature, salinity, fluorescence and transmission readings and water samples for nutrient values were taken, using a CTD rosette (see method here). The water samples collected were used to measure nitrate, phosphate, silicate, dissolved oxygen and observe phytoplankton, which was investigated onshore in the labs.
Plankton net trawls were carried out to assess the diversity and abundance of zooplankton living in the specific areas. The diameter of the zooplankton net was 50cm with a mesh size of 200µm. On the Conway, the net was towed behind the boat, just below the surface for five minutes at a time. The nets were washed at each recovery ensuring the majority of zooplankton collected by the net was transferred into the sample bottle. A flowmeter was attached to the net so that the distance travelled and number of revolutions could be calculated.
A Secchi disk was used to calculate light attenuation at sites 2, 3 and 4 (on board the RV Conway). Once the secchi disk was deployed, the disk was lowered until it was not visible; the depth was estimated by using markings on the rope. This technique is a rough estimation of light attenuation and so could be subject to human error. The values obtained from the secchi disks were corrected to calculate light attenuation using this formula: 1.44 ÷ secchi depth.
An ADCP (on board the research vessel, Conway), was used to monitor the speed and direction of flow at each station. ADCP transects were taken at each station and between stations including transects across the river.
Winnie the Pooh -
Niskin bottles were used at the 4 stations to collect water samples to obtain information of nutrient concentrations (phosphate, silicon, nitrate) and chlorophyll. On the Winnie the Pooh, two zooplankton trawl were taken; one through the lock, travelling upstream and one trawl downstream near Truro. No ADCP values were collected on board the RV Winnie the Pooh, because there was no ADCP available. No Secchi disks were deployed on board the RV Winnie the Pooh.
The views expressed here are not representative of the University of Southampton.