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Falmouth 2017 - Group 12 7TITLE

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Time: 08:37- 14:55 UTC.

Date: 07/07/17

Location: 50º 08’.67” N

005º 01’43” W

Weather: No cloud cover, tempertaure was constant 19°C

Tide: A neap tide with high tide at 04:57 & 17:17 UTC and low tide at 11:27 & 23:49 UTC with a max depth of 4.76m

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ESTUARY (PONTOON AND CONWAY) BACKGROUND & METHODOLOGY

BACKGROUND:

The estuary was examined in two different ways. Firstly, a 3 hour time series of data was collected from the King Harry’s pontoon (near the mouth of the estuary) on 7/7/17 from 8:32 to 11:34 UTC. Here we deployed a multiprobe, current meter, light sensor and niskin bottle that were used to monitor biological, physical and chemical changes over the course of the 3 hours at a fixed location over a tidal cycle. Mainly the key factors being investigated in relation to the tidal cycle were current, depth, temperature, pH, chlorophyll concentration, oxygen saturation and turbidity. The recordings were taken at hourly or half-hourly (multiprobe) intervals, the max depth was measured at 08:37 UTC at 4m. Falmouth experiences a semi-diurnal tidal cycle and on 7/7/17 there was a neap tide with high tide at 04:57 & 17:17 UTC and low tide at 11:27 & 23:49 UTC with a max depth of 4.76m. The weather was good with low cloud cover (2/8), long spells of intense sunshine and low wind.

Secondly, the distribution of nutrients in relation to the estuary’s biological (zooplankton numbers and chlorophyl), chemical (dissolved o2, Si, and PO4/NO3) and physical (depth, temperature and salinity) parameters in the estuary. R.V. Bill Conway took horizontal and vertical transects over length of the estuary with four samples (numbers 26-29) using an ADCP, CTD and zooplankton nets. These were taken from Lat 50°12.171N Lon 005°02.429W to Lat 50°08.674N Lon 005°01.431, from 12:56 UTC to 14:55 UTC. The weather was fair with high cloud coverage (7/8) and low wind. A zooplankton net was used to collect three zooplankton samples from different sites, their location determined by examining the CTD profiles and investigating areas of particular interest. The zooplankton net had a 50cm diameter, and a 200µm mesh size and was towed for five minutes. A flowmeter was attached to the net which displayed numbers of revolutions, each equating to 0.3m tow distance, so that the volume of water sampled can be calculated. Mixing of fresh and saltwater may be expected further up the channel, possibly leading to stratification due to the Fal being a tidally dominant estuary rather than riverine dominated. High values of nutrients, in particular phosphate, may be expected due to the input from the Newham sewage treatment works at the lower salinities; and at higher salinities it may be related to fertilizer run-off, however in the preceding days there was very low precipitation meaning this effect may have been weaker. Furthermore high levels of sunlight during the course of sampling and over the preceding week, may have led to a strong phytoplankton presence as sunlight would have not acted as a limiting factor.

METHODOLOGY:

CONWAY

From CTD Rosette, water samples were taken with niskin bottles at different depths from which the samples were extracted into labelled containers. Either 3 or 4 depths samples were taken depending on depth. Firstly a syringe was washed out with the sample water at least twice, then the 50ml of water sample was extracted into the syringe with the 2µM filter screwed to the end, and flushed out. The filter paper was then extracted and inserted into a tube containing acetone, which was repeated twice more. This process was then repeated again for the other depths and was repeated at each of the 4 stations.

The water from the Niskin bottles attached to the CTD rosette was collected, there were 2 Niskin bottles fired at each depth. For the first 3 stations there were 3 depths sampled, deep, mid and surface samples. For the fourth station, surface, above thermocline, below thermocline and deep were collected.

One sample was collected from each Niskin bottle at each station the jugs were rinsed a couple of times. The syringes and the bottles were rinsed with the sample and the filtered sample respectively, twice to avoid cross contamination. The samples were then syringed through a piece of filter paper to avoid any phytoplankton entering the bottles which could deplete the nutrients in the sample.

The numbers of the bottles were recorded for each separate sample. For silicon samples a plastic bottle was used to avoid any small glass particles entering the sample due to contact with the silicon particles. Brown glass bottles were used for the nitrate and phosphate samples.

After bottling the samples we used a wireside multi-probe 600 QS model to measure temperature and salinity at each depth and station.

PONTOON

A horizontal niskin bottle was deployed off the side of the pontoon and lowered to a depth of 1m and fired. The sample was then taken back up to the surface for further analysis; by attaching a screw on 2µM filter, 50ml of the water sample was flushed through. The filter paper was then extracted and inserted into a tube containing acetone. The niskin bottle was then emptied and reset, and deployed again to a depth of 3m immediately after (as near to the bottom as possible, dependent on tide). Each sample was placed into a labelled container and using a syringe, was rinsed out with the water sample. For each deployment the time of the bottle entering the water was recorded (UTC), these sets were repeated hourly from 8:30 to 11:30 – four sets in total. A horizontal niskin bottle was used due to the shallow water depth.

At 1 hour intervals the current-meter was lowered just below the surface and the speed and direction of the current was recorded. This process was repeated at a depth of 3 m.

The light profile was taken to examine the light attenuation at the pontoon over the course of the day which affected by things such as turbidity, chlorophyll concentration etc. This was carried out every hour using two sensors that measured light intensity, one that remained on the deck and one that was lowered at 1m intervals starting just below the water surface. The use of these two sensors meant that when there was cloud cover this didn’t affect the results as we can calculate the relative ratio between the two sensors.

We deployed the multi-probe off the side of the pontoon and lowered it to the surface of the water where we wrote down the time (UTC) and measured depth (m), temperature (0C), oxygen concentration (%) and (mg/L), salinity (ppt), pH, turbidity (NTU) and chlorophyll concentration (µg/L). We did this at 1m intervals, writing down the time and measurements at each, until we reached the seabed which was around 4m depending on the tide height. We took these readings with the multi-probe every half hour from 8:30 until 11:30 at the different depths.