The study focused on the impacts of catchment development on estuaries. Our previous NESP NAER study showed that for three rivers in the Gulf, nutrient addition to intertidal mudflat cores stimulated production and by inference, a reduction in nutrients,e.g. increased extraction of water, would negatively impact primary production. The current study expanded this further to examine additional estuaries in northern Australia, i.e. Adelaide and Daly R estuaries, as well as revisiting the Flinders and Norman River estuaries to substantiate that the primary productivity values were similar to the previous study.
This dataset examines the effect of nutrient addition on dissolved oxygen fluxes in mudflat samples in experimental units, and compares this with control treatments, and those where surface water has been exchanged with low nutrient water. This study substantiates previous research by Burford & Faggotter showing that estuaries in the Gulf of Carpentaria and NT are impacted by a reduction in nutrient availability, such as would occur when water development reduces available flow and nutrient loads.
There is little knowledge of the links between catchment nutrients and estuarine productivity throughout northern Australia. This means it is impossible to predict how catchment development, such as water extraction, will impact on estuarine productivity. This study is an important step in establishing that link at four estuary systems.
Methods:
Sediment cores (4.5 cm dia . 3 cm deep) were collected from mudflats using perspex tubes and bungs. These cores, with overlying water, were then used for incubations to measure oxygen fluxes. There were treatments with:
1. No nutrients added (5-6 replicate cores)
2. Overlying water periodically replaced with low nutrient water (5-6 replicate cores)
3. Nutrients added (5-6 replicate cores)
Ammonium chloride solution, to give a final concentration of 1.8 mg N L-1, was added to overlying water of each core. Sodium dihydrogen phosphate solution, to give a final concentration of 0.25 µmol P L-1, was also added. The low nutrient source, treatment 2, came from water collected in deeper oceanic waters, i.e. > 30 m deep where nutrient concentrations are typically at or below detection limits.
After 2 days incubating in ambient light (full sun with the light intensity logged) in nally bins with temperature controlled conditions, i.e. 30°C. This was achieved with temperature controller units. All cores were completely filled with either estuarine water from the site or low nutrient water depending on the treatment, so no air remained, and capped so they were completely sealed.
Presens® fiber-optic oxygen sensor (FIBOX) and oxygen-sensitive optode patches glued to the inside wall of each core (Presens) and were used to measure oxygen concentrations multiple times for in each core from early morning through to midday. The times and frequency were based on the rate of change and amount of algae present in the cores at the time of the study.
After each day when rates were measured, the cap was removed and incubations continued for additional days. After this time the same process of measuring daytime DO changes was repeated. This was done to examine how DO fluxes change over time in response to the treatments.
Oxygen production (and consumption in the dark controls which were completely shaded with black plastic) was calculated based on the rate of change of oxygen concentrations during the incubations over each morning graphed against time and then fitted with a linear curve to give mg/l/h. This was then standardized to the surface area of sediment to standardise to mg/m2/h.
Previous studies have demonstrated that the oxygen consumption rates are very low, and typically below detection limits. Therefore only the oxygen production rates are presented.
This study is a VARIATION of the method used in Burford, M.A., Faggotter, S.J. 2021. Comparing the importance of freshwater flows driving primary production in three tropical estuaries. Marine Pollution Bulletin, 169, 112565
Limitations of the data:
This is an experimental unit designed to compare treatments in the short term. It will not accurately represent the rates in the field site or longer term trends, but is most useful for comparative purposes.
Like many experimental studies there are some gaps in sites, treatments and replicates due to poor quality cores or lost cores resulting in no data (blank cells)
The blank cells are because the cores were lost so there is no data. Raw data is inappropriate to include as it requires expertise to determine which datapoints should be used to fit the curve.
Format of the data:
One excel file with columns for date, sites, rivers, flux data
Data dictionary:
Estuary – Name of the estuary the core samples were collected from
Expt_completion_date – date of the end of the incubation period
Site – Site number for the sample (1, 2 or 3)
Treatment – Treatment type for the sample (control, low nutrient, high nutrient)
Rep – replicate of the sample treatment
Days_incubating – number of days the sample underwent incubation before O2 sampling (once sealed)
O2_flux_mg/l/h – calculation based on the rate of change of oxygen concentrations, standardized to the area of sediment, and expressed per unit time for Oxygen production
eAtlas Processing:
The original data were provided as an excel file. The excel file was converted to a csv file. No modifications were made to the underlying data.
Location of the data:
This dataset is filed in the eAtlas enduring data repository at: data\custodian\3.4_Managing-catchment-runoff
