The conceptual models were compiled by researchers in collaboration with a wide range of stakeholders from Natural Resource Management groups, universities and government agencies and based on available scientific information.
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Mangroves are vegetated, intertidal wetlands located at the interface between the land and sea, usually at the mean high-water level. Mangroves are periodically inundated by tides, which are regularly or intermittently diluted with freshwater run-off from the land. They form dense forests with scarce understory vegetation, although, in mangroves with high inputs of freshwater, shrubs or palms can be found. The broadest variety of mangrove species are usually found in tropical, river-dominated forests. Mangroves exist in a constantly changing environment, directly affected by marine and freshwater and are sporadically exposed to floods of freshwater during wet periods.
Key Messages for mangroves and Nitrogen processing
Nitrogen (N) is required by plants and animals, and mangrove growth is usually limited by a lack of N. Additional N can be processed by mangroves, providing a vital ecosystem service, however excess N can also cause negative impacts on their ability to function.
Mangrove forests are highly productive, and are a major long-term sink for N, which can be rapidly consumed, especially during wet periods of the year.
The high productivity of mangroves results in high litter (i.e. fallen leaves) production that can be exported through trophic processes or tidal exchange to the coastal zone in the form of particulate and dissolved organic nitrogen (PON and DON).
Mangrove forests have soils that are rich in carbon and are usually anoxic due to frequent flooding. Due to low oxygen concentrations and redox in mangrove soils, N is usually in its reduced forms, such as ammonium (NH4+). Some of this N can be exported through tides during dry periods of low plant uptake or where DNRA is the dominant process.
Mangrove soils are a long-term sink of N. The soils accumulate organic N mostly from the tissue of dead roots and litter and particulate material transported from the catchment and the sea. The N accumulated in mangrove soils can be stored for decades or even centuries, provided the sediment is not disturbed.
Transformation of N to nitrogen gas in mangroves mostly occurs during wet periods, when freshwater and high nitrate loads can inundate them. During these periods, denitrification can remove large amounts of nitrate (NO3-) from the floodwater, and trees may remove NO3- and ammonium (NH4+).
Mangroves can have significant populations of birds and other animals, but overall these sources of N to the wetland are relatively minor, but highly variable, and usually localised.
Nitrogen fixation tends to be low in mangroves, especially in sites with high N inputs.
The condition or state of mangroves can affect how the system processes N. Excessive N loads, significant amounts of sediment, feral animals, and changes to hydrology can have large impacts on the efficiencies of the system, such as reducing its efficiency for N removal and increasing emissions of N2O (a greenhouse gas).
The processing of N by mangroves is affected by the concentration of N entering the wetland, with higher uptake at higher N loads.
Many landscape features affect how any individual mangrove processes N. Mangroves can be either tidal or river-dominated, so they will receive different amounts of N from their catchment. Usually, mangroves at the mouth of rivers receive much higher N loads and freshwater flows than mangroves that are only inundated by tidal water.
Tidal inundation frequency, amplitude, extent and depth, as well as the location of a mangrove forest in the intertidal zone will affect its connectivity with freshwater (riverine, runoff and groundwater) and marine water. These characteristics will affect the amount of dissolved and particulate nutrients entering the mangrove forest.
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Last updated: 31 July 2021
This page should be cited as:
Department of Environment and Science, Queensland (2021) , WetlandInfo website, accessed 30 August 2021. Available at: https://wetlandinfo.des.qld.gov.au/wetlands/ecology/processes-systems/nitrogen-concept-model/mangrove/