Dissolved inorganic nitrogen, nitrate & ammonia (GBR4 BGC v4.2 baseline)

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    Data gap notice

    Some dates in the 4km eReefs BioGeoChemical model v4.2 dataset have been removed because the model output for those dates was found to be inaccurate, as shown in this sample video.

    The following date ranges have been removed:

    Start date End date
    2 Jan 2011 31 Jan 2011
    2 Feb 2012 2 Mar 2012
    9 Mar 2013 7 Apr 2013
    1 Mar 2014 30 Mar 2014
    6 Apr 2015 5 May 2015
    10 May 2016 8 Jun 2016
    14 Jun 2017 13 Jul 2017
    19 Jul 2018 17 Aug 2018
    23 Aug 2019 21 Sep 2019
    26 Sep 2020 25 Oct 2020
    31 Oct 2021 29 Nov 2021
    19 May 2022 17 Jun 2022

    Please use caution when interpreting the videos in the player above.

    Although the obviously inaccurate dates have been removed, the model may take some time to recover after each disruption. As a result, data in the days and weeks following the removed periods may also be affected. The 30-day buffer used here is a visual estimate and not scientifically validated, so some remaining inaccuracies may still be present in the dataset.

    We will update this portal when corrected model output becomes available.

    This visualisation shows modelled nitrogen levels from the CSIRO eReefs Biogeochemical model. Nitrogen is a key limiting nutrient in the growth of plants and algae. Coral reefs are generally nutrient poor environments with much of the nutrients being locally recycled. Increased nutrient levels promote the growth of phytoplankton, turf algae and macroalgae, inhibiting the rate of recovery of coral reefs.

    The BGC model tracks the transformation of nitrogen through the nitrogen cycle, from fixing of nitrogen gas into ammonia by trichodesmium, to its uptake by plants, propagation through the food chain to zooplankton, to release due to mortality and finally denitrification back into nitrogen gas.

    The BGC model contains two forms of dissolved inorganic nitrogen (DIN), dissolved ammonia (NH4) and dissolved nitrate (NO3): DIN = [NH4] + [NO3]. In the model, the ammonia component of the DIN pool is assumed to be taken up first by all primary producers (phytoplankton, trichodesmium, macroalgae and seagrass), followed by the nitrate, with the caveat that the uptake of ammonia cannot exceed the diffusion limit for ammonia. The underlying principle of this assumption is that photosynthetic organisms can entirely prefer ammonia, but that the uptake of ammonia is still limited by diffusion to the organism’s surface.

    Nitrification is the oxidation of ammonia (NH4) with oxygen, to form nitrite followed by the rapid oxidation of these nitrites into nitrates (NO3). In the BGC model nitrification occurs in the water column and sediment depending on oxygen levels.

    Photosynthetic growth is determined by concentrations of dissolved nutrients (nitrogen and phosphate) and photosynthetically active radiation. Autotrophs (seagrass, phytoplankton, macroalgae and trichodesmium) take up dissolved ammonium, nitrate, phosphate and inorganic carbon. Ammonia is preferentially taken up as a source of nitrogen over nitrate as it can be directly used by plants. Nitrogen is transported through the phytoplankton to zooplankton food chain. Nitrogen is released as ammonia when an organism decays. Trichodesmium fixes nitrogen, converting nitrogen gas N2 into ammonia NH3 when the DIN concentration falls below a critical concentration.

    Dissolved Inorganic Nitrogen

    Concentration of dissolved inorganic nitrogen (DIN). DIN = [NH4] + [NO3].

    Nitrate

    Concentration of nitrate. In the absence of nitrite [NO2-] in the model, nitrate represents [NO3-] + [NO2-].

    Ammonia

    Concentration of ammonia ions [NH4+].

    Source data

    The videos/images on this page are based on the 4km eReefs BioGeoChemical model (v4.2) run with SOURCE Catchments using Baseline catchment conditions. The model builds on the CSIRO Environmental Modelling Suite (EMS), described in the paper: Scientific description of the optical and biogeochemical models (vB3p0). The dataset metadata is available from the NCI GeoNetwork: eReefs GBR4 Biogeochemistry and Sediments v4.2 baseline catchment scenario. The raw model data is available from the NCI THREDDS server (daily, in curvilinear NetCDF format).

    Data span

    These results are based on a fixed time period (Dec 2010 - Apr 2019) hind-cast analysis developed for comparing changes in land practices. The river runoff used to drive the BGC model was provided by the SOURCE Catchments modelling.