Derwent Estuary water sampling (KSA224 assessment 2025)

The aim of this trip was to investigate the salt wedge of the Derwent estuary, looking at the different properties along and across the estuary. This was achieved by examining; temperature, salinity, chlorophyll-a concentration, nutrients (including nitrate, ammonia, phosphate and silicate), pressure, turbidity, fluorescence, dissolved oxygen and pH. Sampling took place in the morning, in sunny, relatively calm conditions with the low tide on the sampling day at approximately 11:04 am. Two transects were used, with three different locations tested along the estuary and four tested across, at the approximate locations: (-42.94014, 147.38385), (-42.96321, 147.57525), (-42.98388, 147.37083), (-42.9795, 147.336), (-42.9744, 147.3585), (-42.97594, 147.36394) and (-42.97616, 147.38914). Sampling consisted of CTD sensor measurements, a plankton net tow, Secchi disk measurements, and a collection of water samples for analysis.

Identification info

Date (Publication): 2025-05-27T00:00:00

Resource provider

Institute for Marine and Antarctic Studies (IMAS)

Private Bag 129

Hobart

Tasmania

7001

Australia

Author

Institute for Marine and Antarctic Studies - Wooldridge, Zoe

IMAS - Hobart

Private Bag 129

Hobart

TAS

7001

Australia

Collaborator

Institute for Marine and Antarctic Studies - McLachlan, Brooke

IMAS - Hobart

Private Bag 129

Hobart

TAS

7001

Australia

Collaborator

Institute for Marine and Antarctic Studies - Aulich, Bridie

IMAS - Hobart

Private Bag 129

Hobart

TAS

7001

Australia

Credit: KSA224/324 Oceanographic Methods class 2025 (IMAS)

Status: Completed

Author

Institute for Marine and Antarctic Studies - Wooldridge, Zoe

Private Bag 129

Hobart

TAS

7001

Australia

Point of contact

Institute for Marine and Antarctic Studies - van der Merwe, Pier

Private Bag 129

Hobart

TAS

7001

Australia

ORCID ID >

Topic category

Oceans

Extent

Temporal extent

Time period: 2025-03-27 2025-03-27

Vertical element

Minimum value: 0

Maximum value: 26

Identifier: EPSG::5715

Name: MSL depth

Maintenance and update frequency: Not planned

Keywords (Theme)

Salt wedge

Global Change Master Directory Earth Science Keywords, Version 8.5

Australian and New Zealand Standard Research Classification (ANZSRC): Fields of Research

Resource constraints

Use limitation: Data, products and services from IMAS are provided "as is" without any warranty as to fitness for a particular purpose.

Resource constraints

Linkage: https://licensebuttons.net/l/by/4.0/88x31.png
License Graphic

Title: Creative Commons Attribution 4.0 International License

Alternate title: CC-BY

Edition: 4.0

Website: https://creativecommons.org/licenses/by/4.0/
License Text

Other constraints: The citation in a list of references is: "Citation author name/s (year metadata published), metadata title. Citation author organisation/s. File identifier and Data accessed at (add http link)."

Language: English

Character encoding: UTF8

Content Information

Content type: Physical measurement

Identifier

Code: CTD Data Quality Flag

Name: CTD_data_flag

Name: NA

Identifier

Code: Specific electrical conductivity of the water body

Name: Conductivity

Identifier: http://vocab.nerc.ac.uk/collection/P06/current/UECA

Name: Siemens per metre

Identifier

Code: Density of the water body

Name: Density

Identifier: http://vocab.nerc.ac.uk/collection/P06/current/UKMC

Name: Kilograms per cubic metre

Identifier

Code: Sample Depth

Name: Depth

Identifier: http://vocab.nerc.ac.uk/collection/P06/current/ULAA

Name: Metres

Identifier

Code: Fluorescence of the water body

Name: Fluorescence

Identifier: http://vocab.nerc.ac.uk/collection/P06/current/UMMC

Name: Milligrams per cubic metre

Identifier

Code: Oxidation Reduction Potential

Name: ORP

Name: Millivolts

Identifier

Code: Concentration of oxygen {O2} per unit volume of the water body

Name: Oxygen_mg_L

Identifier: http://vocab.nerc.ac.uk/collection/P06/current/UMGL

Name: Milligrams per litre

Identifier

Code: pH (total scale) of the water body

Name: pH_x

Identifier: http://vocab.nerc.ac.uk/collection/P06/current/UUPH

Name: pH units

Identifier

Code: Saturation of oxygen {O2} in the water body [dissolved phase]

Name: Oxygen_Sat

Identifier: http://vocab.nerc.ac.uk/collection/P06/current/UMGL

Name: Milligrams per litre

Identifier

Code: Potential Temperature

Name: Potential Temperature

Identifier: http://vocab.nerc.ac.uk/collection/P06/current/UPAA

Name: Degrees Celsius

Identifier

Code: Pressure (measured variable) in the water body exerted by overlying sea water only

Name: Pressure

Identifier: http://vocab.nerc.ac.uk/collection/P06/current/UPDB

Name: Decibars

Identifier

Code: Practical salinity of the water body

Name: Salinity

Identifier: http://vocab.aodn.org.au/def/unitsofmeasure/entity/481

Name: Practical Salinity Unit

Identifier

Code: Temperature of the water body

Name: Temperature

Identifier: http://vocab.nerc.ac.uk/collection/P06/current/UPAA

Name: Degrees Celsius

Identifier

Code: Turbidity of the water body

Name: Turbidity

Identifier: http://vocab.nerc.ac.uk/collection/P06/current/USTU

Name: Nephelometric Turbidity Units

Identifier

Code: Time Elapsed

Name: Time_Elapsed

Identifier: http://vocab.nerc.ac.uk/collection/P06/current/UTBB

Name: Seconds

Identifier

Code: Chlorophyll Quality Flag

Name: NA

Identifier

Code: Concentration of chlorophyll-a per unit volume of the water body

Name: Chla

Identifier: http://vocab.nerc.ac.uk/collection/P06/current/UMMC

Name: Milligrams per cubic metre

Identifier

Code: Displaced Volume of Zooplankton

Name: Displaced_volume

Name: Millilitre

Identifier

Code: Dissolved Oxygen (Probe)

Name: DIO

Identifier: http://vocab.nerc.ac.uk/collection/P06/current/UMGL

Name: Milligrams per litre

Identifier

Code: pH (Probe)

Name: pH_y

Identifier: http://vocab.nerc.ac.uk/collection/P06/current/UUPH

Name: pH units

Identifier

Code: Secchi depth

Name: SD_depth1

Identifier: http://vocab.nerc.ac.uk/collection/P06/current/ULAA

Name: Metres

Identifier

Code: Secchi depth

Name: SD_depth2

Identifier: http://vocab.nerc.ac.uk/collection/P06/current/ULAA

Name: Metres

Identifier

Code: Nutrient Bottle QC

Name: Nutrient_Bottle_flag (all nutrients except nitrite)

Name: NA

Identifier

Code: Concentration of ammonium {NH4} per unit volume of the water body

Name: Ammonia

Identifier: http://vocab.nerc.ac.uk/collection/P06/current/UPOX

Name: Micromoles per litre

Identifier

Code: Concentration of nitrate and nitrite {NO3 and NO2} per unit volume of the water body

Name: NOx

Identifier: http://vocab.nerc.ac.uk/collection/P06/current/UPOX

Name: Micromoles per litre

Identifier

Code: Nitrite Flag

Name: Nitrite_flag

Name: NA

Identifier

Code: Concentration of nitrite {NO2} per unit volume of the water body

Name: Nitrite

Identifier: http://vocab.nerc.ac.uk/collection/P06/current/UPOX

Name: Micromoles per litre

Identifier

Code: Concentration of phosphate {PO4} per unit volume of the water body

Name: Phosphate

Identifier: http://vocab.nerc.ac.uk/collection/P06/current/UPOX

Name: Micromoles per litre

Identifier

Code: Concentration of silicate {SiO4} per unit volume of the water body

Name: Silicate

Identifier: http://vocab.nerc.ac.uk/collection/P06/current/UPOX

Name: Micromoles per litre

Distribution Information

Distribution format

OnLine resource: Oceanographic data quality flag schemes

OnLine resource: Go-Ship Hydro Manual

OnLine resource: DATA Download - Derwent Estuary Water Sampling

Resource lineage

Statement: CTD Rosette A CTD rosette was deployed at each location to create a depth profile. Water was also collected at three different depths. At each location a log sheet with time, bottom depth, depth of firing, date and location was completed. At each location the CTD was programmed via the event log on a laptop to fire on the upcast and at specific depths based off input pressures. These pressures corresponded to three depths: one approximately 2m from the bottom, one at the middle and one at 5m. The CTD was turned on prior to deployment to start recording data. After being deployed it was held stationary at 2m depth for calibration before continuing with the descent. Once reaching the bottom it was brought up and fired at the three pre-ordered pressures. After returning to the surface the CTD was turned off and samples of each depth were placed into previously labelled sample bottles for further analysis. Oxygen (125mL BOD bottle), pH (100mL container), nutrients (2 x 10mL tubes) and chlorophyll (500 mL amber bottle) were taken in this order. All sample bottles were rinsed three times with the sample water before the final sample was added. Water Measuring The water samples from the CTD at each location and depth were measured for oxygen and pH. The oxygen and pH probes were prepared by rinsing with deionised water. The oxygen was recorded straight after receiving the sample, with measurements taken after the probe stabilised. Two replicates for each sample were taken. The pH was recorded afterwards, with three replicates for each sample being taken. All measurements were recorded on a pre-prepared log sheet. Filtration and chlorophyll samples A filter rig was prepared with filters for three samples. 500mL chlorophyll samples from the CTD Niskin bottles were filtered. The filter was then placed into previously labelled extraction vials using forceps. These vials were immediately wrapped in aluminium foil and placed on ice for analysis later. This was repeated for each location’s new chlorophyll samples. Later the chlorophyll was extracted from the filters through adding 90% acetone and leaving it for 24 hours. The sample was then analysed by a fluorometer. Secchi disk The Secchi disk was lowered off the sunny side of the boat with two designated observers watching. Once the disk could no longer be seen by either observer it was slowly pulled up. The distance of the rope, from the ocean’s surface to the Secchi disk, when each observer could see the disk again was recorded. The measurements along with time, observer and conditions were recorded on a log sheet. This was then repeated at each location. Plankton tow At each location the flow meter reading was recorded prior to deploying the plankton net off the back of the boat. It was then towed for a couple of minutes before being bought back in where the flow meter reading was recorded again. The net was rinsed down and the displaced volume was recorded (volume of whole sample – volume of water only) after filtering the sample. The sample was homogenised, and one drop was placed on a counting cell where it was observed under a microscope with notes taken if Gymmnodinium catenatum was found. All measurements and mesh size of plankton net were recorded on a log sheet. Nutrient Analysis Nutrients were analysed by the lab at CSIRO Hobart. This included using a AA3 segmented flow analyser. Prior to running the samples through the machine, the analyser was calibrated using six standards at the start of the run before running a quality control. Methods were synchronous to Go-Ship Hydro Manual recommendations for nutrient analysis. Note: Nitrite samples were corrected using CSRIO Hobart's standard programming for a baseline shift in the instrument, some results had a shift in baseline which exceeded the expanded uncertainty, so these should not be used in publications, this was shown by data quality flags. Data Analysis Data quality flags were created for the CTD data, chlorophyll data and nutrient data. The flags followed guidelines by the ODV generic quality flags scheme in which; 0=good quality, 1=unknown quality, 4=questionable quality and 8=bad quality.

Hierarchy level: Dataset

Hierarchy level: Dataset

Metadata

Metadata identifier: urn:uuid/df44feb3-ec6b-4cd1-b72f-b07a8bf2428e

Language: English

Character encoding: UTF8

Distributor

IMAS Data Manager - Data Officer

Institute for Marine and Antarctic Studies

Private Bag 129

Hobart

Tasmania

7001

Australia

Institute for Marine and Antarctic Studies (IMAS) website >

Type of resource

Resource scope: Dataset

Name: IMAS Dataset level record

Metadata linkage: https://metadata.imas.utas.edu.au/geonetwork/srv/eng/catalog.search#/metadata/df44feb3-ec6b-4cd1-b72f-b07a8bf2428e
Point of truth URL of this metadata record

Date info (Creation): 2025-03-27T00:00:00

Date info (Revision): 2025-06-05T08:12:22

Metadata standard

Title: ISO 19115-3:2018

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