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Estuary




The Falcon spirit sampled across a large portion of the estuary, from Cremyll (Station H) at a latitude of 50°21.812N and a longitude of 004°10.331W to the Eastern Channel (Station J) at a latitude of 50° 20.105N and a longitude of 004°08.111W. There were 9 stations in total (B-J). Sampling started at 8:17 UTC at the first station and ended at 1:29 at the Station J.


Method


While at each station the CTD was deployed and a number of the Niskin bottles were fired at different depths to collect water samples. Oxygen, silicon, phosphate, chlorophyll and phytoplankton samples were then taken and an ADCP transect was set up. Secchi disk measurements were also taken to determine turbidity.

Conditions were slightly windy in the morning and sunny, with little cloud cover (0/8 to 1/8 in some areas). Temperatures reached up to 27°C. The sea state was relatively calm, with the wind earlier in the day resulting in the boat to experience a small amount of drift when deploying the CTD.  High tide occurred at 10:45 UTC and low tide occurred at 4:22 UTC. Therefore, the measurements for the first four stations (H, F, D & B) were taken before high tide and the rest taken during high tide.


The purpose of sampling along the whole estuary was to allow for a comparison to be made between the mixing diagrams of the different nutrients and the number and diversity of the phytoplankton as the salinity and temperature changes in different parts of the estuary. Areas of mixing or stratification can be identified and a whole estuary profile can be determined.


For Oxygen sampling methodology and analysis please see the Offshore tab.





A three team analysis of the Tamar Estuary was conducted, using two research vessels and a pontoon:

- Falcon Spirit, Plymouth University boat, capable of deploying a CTD with a Niskin bottle rosette and with an onboard lab for processing water samples.

- Winnie the Pooh, another Plymouth University boat, of small size, capable of penetrating further up the Estuary. It collected a range of water samples and readings.

- The pontoon, a fixed platform where repeat samples where taken from, providing a data series from a fixed point.


Date: 06/07/2018

Time: 8:30 – 14:00 UTC

Location: 50°40.943N 4°20.556W

Weather: Sunshine with some passing cloud. 7-8mph winds, NW

Tide: High Tide 12:02 BST

Water Depth: 4-5m

A time series measuring irradiance, temperature, salinity, chlorophyll, turbidity, dissolved oxygen, current speed and current direction was carried out from 8:30 to 14:30 UTC at Saltash Pontoon. The aim of this was to investigate the daily variation in these physical and biological properties, which is partly influenced by the tidal change and weather, but also by a number of other factors.



Data Interpretation


Introduction

Biology Physical & Chemical

Method


A YSI probe was used to measure salinity, chlorophyll, turbudity and dissolved oxygen. Measurements were taken at depth intervals from the surface, every meter to the seafloor. A PAR meter was used to measure irradiance at the surface and at depth every 30 minutes. The flow speed and direction where measured at 1m depth intervals every 30 minutes.

Water samples were collected every hour at 1m and 4m depths using a Niskin bottle. 50ml of the water sample was filtered and placed in tubes containing acetone. They were later analysed using a flouromtere to calculate chlorophyll concentrations. All readings were taken from 8:30 to 14:00 UTC.

Sampling with the PAR and current meter was originally down to 5m but as the tide went out the water level dropped below this so sampling had to be limited to 4m upwards.

Pontoon Data Collection


Winnie the Pooh Data Collection


The upper estuary was sampled from the bridge at Saltash (Station C), with a latitude of 50°24’31.0N and longitude of 004°12.13.0W, past the confluence of the River Tavy and River Tamar, to Station B, with a latitude of 50°26’12.1N and a longitude of 004°11’48.4W, up to Calstock (Station A), with a latitude of 50°29’43.9N and a longitude of 004°12’24.7W.


The Winnie the Pooh moved upriver on the rising tide, reaching Calstock at 10.15 UTC. Sampling started at 10.49 UTC off the dock at Calstock, before moving upriver in search of fresher water. Conditions were sunny with a slight breeze throughout the sampling period. Having sampled a salinity of less than 5, we then turned and headed down river, sampling every time the salinity changed by roughly 2psu. The last sample was taken by the bridge at Saltash at 14.25 UTC, about midway through the falling tide.


The reason for sampling the upper estuary was to see how nutrients, chlorophyll and plankton change with the full change in salinity. It also allowed us to see how much the River Tavy inputs to the Tamar estuary, and see what impact the dockyards and industry further down the estuary have on the phytoplankton and nutrients.


Map of the location of stations C to J sampled on the Falcon Spirit, Winnie the Pooh and the Pontoon

Falcon Spirit Data Collection