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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Palustrine wetlands are what many people traditionally think of as a wetland—they are vegetated, non-channel systems that are not influenced significantly by tidal waters. They are usually relatively small (often less than 8 ha) and have over 30% emergent vegetation cover, including trees, shrubs, grasses and sedges. Palustrine wetlands include billabongs, swamps, bogs, springs, and soaks. They can occur in both floodplain and non-floodplain landscapes and can be ephemeral, seasonally or permanently inundated. Palustrine wetlands are usually shallow (less than 2 m deep) and excessive water can damage emergent plants. These wetlands provide many ecosystem services including habitat and breeding areas for a wide variety of species.
Key Messages for palustrine wetlands and nitrogen processing
Nitrogen (N) is required for the growth of plants and animals in palustrine wetlands. Additional N entering in surface water and groundwater can be processed by palustrine wetlands, providing a vital ecosystem service, however excess N can cause negative impacts on these systems.
There are a very wide range of palustrine wetlands, many of which have features which facilitate the processing of N. These wetlands can convert particulate (PN) and soluble forms (ammonium (NH4), nitrate (NO3), and dissolved organic nitrogen (DON), to N2 gas through processes such as denitrification.
Many palustrine wetlands have ideal conditions for denitrification as they have dense vegetation, biofilms on the vegetation, and soils that are temporarily anoxic. These soils are generally rich in carbon, sometimes forming peat that can reach up to one meter in depth. As a result, these types of palustrine wetlands are major transformers of N.
Palustrine wetlands do not generate significant amounts of N, as microbial fixation (the only process that can generate N in wetlands) is a minor process in these systems.
Trees in palustrine wetlands provide long-term storage of N, and aquatic plants, grasses, herbs and shrubs provide short-term storage. The N accumulated in vegetation can partially be returned to the soil where it forms litter, which can be remineralised or exported.
Soils in palustrine wetlands accumulate organic N from plant growth and decay, but they can also accumulate N deposited from external sources such as sediment and vegetated litter delivered when the wetland is inundated during rainfall events and flooding. A risk to palustrine wetlands is excess sediment and particulate N that can fill the wetlands up.
The N stored in the soils is accumulated over time, but some of it can be released into the water column through mineralisation and ammonification – this is not considered generation of N as the sediment was deposited from external sources.
The hydrology of the wetland is critical for N processing. Many palustrine wetlands are inundated by pulses during rainfall events, and water residence time can vary from days to months. During the dry season, palustrine wetlands can receive water flows through groundwater inputs.
Permanently wet palustrine wetlands can process N continually. Systems receiving flood pulses with N rich water will process it at a rate depending on the soil and vegetation characteristics of the wetland and the amount of N entering the system. Ephemeral systems are usually less efficient at processing N due to lack of inundation.
Denitrification in palustrine wetlands can occur within hours of N entering the wetlands, even if it was relatively dry beforehand.
The rates of N transformation by denitrification in palustrine wetlands are usually calculated by considering the area of the wetland rather than the volume, as these wetlands are relatively shallow and most of the water is in contact with the soils and vegetation, where denitrification is highest.
During periods of flooding, palustrine wetlands will become hotspots of nitrogen removal as denitrification will rapidly remove nitrate from the water column, especially in the interface between soil and water, and in the biofilm (algae and bacteria growing over vegetation or other substrates).
While palustrine wetlands can have significant populations of birds and other animals, these sources of N input to the wetland are relatively minor, highly variable, and usually localised. In the Great Barrier Reef catchments, pigs contribute to localised increases in N via pig faeces.
The condition or state of the wetlands can affect how the system processes N. High infestations of weeds, significant amounts of sediment, feral animals, anaerobic conditions (no oxygen) and changes to hydrology can have large impacts on the efficiencies of the system to process N.
Healthy palustrine wetlands primarily produce N gas from denitrification (N2), but wetlands with high N loads and anaerobic conditions can generate N2O, a greenhouse gas, and NH3, which is toxic to aquatic fauna.
The processing of N by palustrine wetlands is affected by the concentration of N entering the wetland, with higher transformations at higher concentrations in carbon rich soils.
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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 26 September 2022. Available at: https://wetlandinfo.des.qld.gov.au/wetlands/ecology/processes-systems/nitrogen-concept-model/palustrine/