Estuary

Southampton University Falmouth 2015

Group 13

Home Offshore Estuary Pontoon Habitat Mapping

Estuaries are dynamic systems that vary not only spatially but also temporally. This is due to tides being their predominant driving force, in fluxing the estuary with sea water twice a day. The impact of the tides is seen across a wide range of measurable quantities in the estuary which together provide a portrait of a constantly changing estuary.

These transformations in estuarine composition have an intrinsic link to the biota that inhabit the estuary. Harris (1980) showed that short-term variability of phytoplankton can be of the same magnitude as those changes in biomass seen over much longer time scales. In addition to this, the dynamic nature of the estuary affects faunal species, with most brackish water species showing the ability to survive at a large range of salinities, these animals are known as euryhaline organisms

Disclaimer: The views and opinions expressed are those of the individual and not necessarily those of the University of Southampton or the National Oceanography Centre, Southampton.

Methodology

At each station several factors were investigated:

1. The first equipment deployed was a CTD rosette, used to take samples through the water column. The CTD bottle used 3 bottles (Bottle 2,3 and 6) as there were only 3 Niskin bottles in working condition attached to the CTD rosette. Specific depths were selected on deck and between 2 and 3 samples were taken, including one at the surface and at the bottom. Where there was a fluctuation or abnormality in a particular parameter another sample was taken. The samples were returned to the surface and preserved for analysis.

2. A transect was followed across the estuary to use the ADCP. This then allowed the analysis of flow, current velocity and backscatter of particles in the water column using Winriver software.

3. At each site a secchi disk was deployed. This was lowered until reaching a depth where it was no longer visible with the naked eye. The rope was marked enabling the estimation of depth, however the use of the human eye meant this the result is open to human error.

4. The zooplankton net was deployed from the vessel for 5 minutes at the surface. The net was then rinsed to ensure that all zooplankton were moved from the net into the sample bottle. However, some zooplankton will not have been flushed into the bottle and this must be taken into account.

Chemical Analysis process:

Oxygen: Water samples were collected directly from the Niskin Bottles, and the water samples were processed as standard procedure according to Grasshoff et al., 1999. For stations 42, 43, and 44, only one oxygen sample was taken at mid depth (4.5, 8.253, and 14.25 meters respectively). At the final station, station 45, samples were taken at all depths at 0.974, 7.667, and 19.6 meters.

Chlorophyll: Three replicate water samples were taken at each station for all depths. 50 mL of water was filtered using a syringe. The filter was then placed into 6 mL of acetone.

Phytoplankton: At stations 42 and 45G, water samples were added to glass bottles containing 10 mL of Lugol’s Iodine. The iodine kills and stains the phytoplankton so it can be easily examined under a microscope.

References

Grasshoff, K., K. Kremling, and M. Ehrhardt. (1999). Methods of seawater analysis. 3rd ed. Wiley-VCH.

Harris, G. (2015). Temporal and Spatial Scales in Phytoplankton Ecology. Mechanisms, Methods, Models and Management - Canadian Journal of Fisheries and Aquatic Sciences. Canadian Journal of Fisheries and Aquatic Sciences.

27/06/2015

High tide: 00:29 and 13:17 UTC at a depth of 4.2m

Low Tide: 07:18 and 19:46 UTC at a depth of 1.7m

Weather conditions: Sun with a light wind and light cloud cover