Mangrove

Mangrove

 

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[5].

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Mangroves

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.

For definitions of wetland systems see the System Definitions page

For wetland ecosystem services information see the Wetland Values page

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[13][10].
• 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[1].
• 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)[2]. 
• 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⁺)[9]. Some of this N can be exported through tides during dry periods of low plant uptake[9] or where DNRA is the dominant process[8].
• Mangrove soils are a long-term sink of N. The soils accumulate organic N mostly from the tissue of dead roots and litter[11] and particulate material transported from the catchment and the sea. The N accumulated in mangrove soils can be stored for decades or even centuries[3], provided the sediment is not disturbed.
• The processes in mangrove soils known for removing N are denitrification and anaerobic ammonium oxidation (anammox). Both processes convert either N as nitrate (NO_3-) or NH₄⁺ to N gas[7]. Another microbial process, DNRA (dissimilatory nitrate reduction assimilation), or conversion of NO or NH₄⁺could also result in export of NH₄⁺ from mangrove soils[1][14].
• 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 (NO_3-) from the floodwater, and trees may remove NO_3- and ammonium (NH₄⁺)[14].
• 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[6].
• Nitrogen fixation tends to be low in mangroves, especially in sites with high N inputs[10].
• 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)[15][12].
• The processing of N by mangroves is affected by the concentration of N entering the wetland, with higher uptake at higher N loads[4].
• 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[1].
• 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[1][12].

References

1. ^ a b c d Adame, MF, Virdis, B & Lovelock, CE (2010), 'Effect of geomorphological setting and rainfall on nutrient exchange in mangroves during tidal inundation', Marine and Freshwater Research, vol. 61, no. 1197-1206.
2. ^ Adame, MF & Lovelock, CE (2011), 'Carbon and nutrient exchange of mangrove forests with the coastal ocean', Hydrobiologia, vol. 663, pp. 23-50.
3. ^ Adame, MF & Fry, B (2016), 'Source and stability of soil carbon in mangrove and freshwater wetlands of the Mexican Pacific coast', Wetlands Ecology and Management, vol. 24, pp. 129-137.
4. ^ Adame, MF, Roberts, ME, Hamilton, DP, Ndehedehe, CE, Lu, J, Griffiths, M, Curwen, G & Ronan, M (2019), 'Tropical coastal wetlands ameliorate nitrogen exports during floods', Frontiers in Marine Science, vol. 6, 1-14.
5. ^ Adame, MF, Vilas, MP, Franklin, H, Garzon-Garcia, A, Hamilton, D, Ronan, M & Griffiths, M (2021), 'A conceptual model of nitrogen dynamics for the Great Barrier Reef catchments', Marine Pollution Bulletin. [online], vol. 173PA. Available at: https://www.sciencedirect.com/science/article/pii/S0025326X21009437.
6. ^ Allaway, WG & Ashford, AE (1984), 'Nutrient input by seabirds to the forest on a coral island of the Great Barrier Reef', Marine Ecology Progress Series, vol. 19, pp. 297-298.
7. ^ Burgin, AJ & Hamilton, SK (2007), 'Have we overemphasized the role of denitrification in aquatic ecosystems? A review of nitrate removal pathways', Frontiers in Ecology and the Environment, vol. 5, no. 2, pp. 89-96.
8. ^ Cao, W, Yang, J, Li, Y, Liu, B, Wang, F & Chang, C (September 2016), 'Dissimilatory nitrate reduction to ammonium conserves nitrogen in anthropogenically affected subtropical mangrove sediments in Southeast China', Marine Pollution Bulletin. [online], vol. 110, no. 1, pp. 155-161. Available at: https://linkinghub.elsevier.com/retrieve/pii/S0025326X16304726 [Accessed 23 August 2021].
9. ^ a b Reef, R, Feller, IC & Lovelock, CE (2010), 'Nutrition of mangroves', Tree Physiology, vol. 30, no. 9, pp. 1148-1160.
10. ^ a b Reis, CRG, Nardoto, GB & Oliveira, RS (January 2017), 'Global overview on nitrogen dynamics in mangroves and consequences of increasing nitrogen availability for these systems', Plant and Soil. [online], vol. 410, no. 1-2, pp. 1-19. Available at: http://link.springer.com/10.1007/s11104-016-3123-7 [Accessed 2 November 2020].
11. ^ Robertson, AI & Alongi, DM (2016), 'Massive turnover rates of fine root detrital carbon in tropical Australian mangroves', Oecologia, no. 180, pp. 841-851.
12. ^ a b Sadat-Noori, M, Santos, IR, Tait, DR & Maher, DT (2016), 'Fresh meteoric versus recirculated saline groundwater nutrient inputs into a subtropical estuary', Science of the Total Environment. [online], vol. 566-567, pp. 1440-1453. Available at: http://dx.doi.org/10.1016/j.scitotenv.2016.06.008.
13. ^ Verhoeven, JTA, Arheimer, B, Yin, C & Hefting, MM (2006), 'Regional and global concerns over wetlands and water quality', Trends in Ecology and Evolution, vol. 21, no. 2, pp. 96-103.
14. ^ a b Wadnerkar, PD, Santos, IR, Looman, A, Sanders, CJ, White, S, Tucker, JP & Holloway, C (2019), 'Significant nitrate attenuation in a mangrove-fringed estuary during a flood-chase experiment', Environmental Pollution. [online], vol. 253, pp. 1000-1008. Available at: https://doi.org/10.1016/j.envpol.2019.06.060.
15. ^ Zhou, S, Borjigin, S, Riya, S, Terada, A & Hosomi, M (2014), 'The relationship between anammox and denitrification in the sediment of an inland river', Science of the Total Environment. [online], vol. 490, pp. 1029-1036. Available at: http://dx.doi.org/10.1016/j.scitotenv.2014.05.096.

Last updated: 31 July 2021