D'Entrecasteaux Channel water sampling (KSA324 assessment 2023)

Brief description

Data were collected by third-year students on a KSA324 field excursion down the D'Entrecasteaux Channel, on the IMAS vessel Noctiluca. The purpose of the trip was for students to learn how to collect various common types of oceanographic data and work on a research vessel. The study was designed to assess the impact of finfish farming in the Channel on local nutrient levels and water quality. The Tasmanian Environment Protection Authority (EPA) methods for water quality monitoring around finfish farms (Ford 2021, p. 6 – 18) were replicated as closely as possible. The null hypothesis for this study was that, on the 17/04/2023, all measured physico-chemical and biological factors were not significantly above the levels specified by the EPA guidelines (Ford 2021, p. 6 – 18), in any of the four stations measured. These four stations were chosen because they were all further than 35 metres beyond the boundary of any finfish farms’ Lease Area, as specified by the EPA guidelines document (Ford 2021, p. 6). The precise latitudes and longitudes of these stations are as follows: M1 (-43.059295, 147.345047); M2 (-43.056057, 147.291386); M3 (-43.123841, 147.290882); M4 (-43.133534, 147.326519). The dataset includes measurements of temperature, conductivity, oxygen concentration, pH, turbidity, fluorescence and pressure taken by the CTD rosette. Depth, density, practical salinity, absolute salinity and conservative temperature were derived and also included. The dataset also contains bottle sample measurements of oxygen, pH and alkalinity, as well as both the total and dissolved concentrations of ammonia, NOx, nitrite, phosphate and silicate. Chlorophyll concentration, total plankton cell counts, and counts of only Gymnodinium catenatum (a toxic, invasive dinoflagellate) cells were also included in the dataset. The dataset also contains the Secchi depth at each station. Empty cells are indicated by “NA”. ODV data flagging convention was used: 0 = good quality; 1 = unknown quality; 4 = questionable quality; 8 = bad quality. Reference: Ford, W (Director for the Environment Protection Authority) 2021, Environmental Licence No. 9869/3, Environmental Licence under the Environmental Management and Pollution Control Act 1994, pp. 6 – 18.

Lineage

Maintenance and Update Frequency: notPlanned

Statement: At each site, the SBE 55 ECO rosette, fitted with the SBE 19plus CTD, SBE 43 DO sensor, SBE 18 pH sensor and ECO fluorometer, was lowered to roughly 1m above the seafloor. On the ascent, in-situ measurements of temperature, conductivity, turbidity, pressure, oxygen concentration, pH and fluorescence were taken every one metre, until the surface. Water samples were also taken by three 5L Niskin bottles on the ascent: the first around 3m above the seafloor; the third roughly 1m below the surface; and the second half-way between the two. From the Niskin water samples, oxygen, pH and alkalinity were measured immediately in that order, from 100mL sample containers, using the HQ 4300 Portable Multi-Meter. Oxygen was measured with two replicates, pH with three replicates and alkalinity only once. Nutrient and chlorophyll samples were also taken from the Niskin bottles, to be analysed in the lab. Nutrient samples were taken according to Tasmanian Environment Protection Agency (EPA) guidelines (Ford 2021, p. 6 – 18). For total nutrient concentrations, one 30mL tube was filled from each Niskin bottle (3 tubes per sampling station), leaving 5mL of head space. The same process was followed for dissolved nutrient concentrations, however the samples were filtered through syringe filter first. Both total and dissolved nutrient samples were immediately placed on ice in an esky. For chlorophyll samples, one 500mL sample bottle was filled from each Niskin bottle (3 bottles per sampling station). The contents of the sample bottle were immediately filtered onto GFF filter paper. Each filter paper was then immediately individually wrapped in foil and stored on ice in an esky. At each site, a plankton net with 20 micrometre mesh was deployed by hand to five metres, then immediately pulled back up. A subsample from the contents of the net was placed onto a microscope slide counting grid, then viewed under an optical microscope. Counts of both total plankton cells and Gymnodinium catenatum cells only were made by two different researchers and average count was recorded. A Secchi disk was also deployed twice at each site, by two different researchers. The mean Secchi depth was recorded for each site. Nutrient and chlorophyll concentrations were measured in the lab. The nutrient samples were analysed at CSIRO laboratories, according to the method of Rees et. al. (2018, pp. 25 – 40). Both total and dissolved concentrations of ammonia, NOx, nitrite, phosphate and silicate were measured using a segmented flow analyser (Rees et. al. 2018, pp. 25 – 40). Chlorophyll concentration was measured in the IMAS laboratory by KSA324 students, according to the method of Yentsch and Menzel (1963, pp. 221 – 231). The fluorescence was measured via acidification using a Trilogy fluorometer, with 90% acetone as the extraction solvent (Yentsch and Menzel 1963, pp. 221 – 231). Using Matlab, depth, density, practical salinity, absolute salinity and conservative temperature were derived from the in-situ measurements taken. Depth and density were derived from pressure; practical salinity and absolute salinity derived from conductivity; and conservative temperature derived from in-situ temperature. Quality control was conducted on the entire dataset. Researchers manually checked measurements in the spreadsheet to ensure all values were roughly as expected. Log sheets were also examined for all notes relating to data quality. The ODV data quality flagging convention was used: 0 = good quality; 1 = unknown quality; 4 = questionable quality; 8 = bad quality. Empty cells were indicated by “NA”. References: Ford, W (Director for the Environment Protection Authority) 2021, Environmental Licence No. 9869/3, Environmental Licence under the Environmental Management and Pollution Control Act 1994, pp. 6 – 18. Rees, C et. al. 2019, ‘Methods for reproducible shipboard SFA nutrient measurement using RMNS and automated data processing’, Limnology and Oceanography: Methods, vol. 17, pp. 25 – 41. Yentsch S, Menzel W 1963, ‘A method for the determination of phytoplankton chlorophyll and phaeophytin by fluorescence’, Deep Sea Research, vol. 10, pp. 221 – 231.

Notes

Credit
IMAS KSA 324 Oceanographic Methods

Credit
KSA324 Oceanographic Methods class 2023 (IMAS)