Mangrove

Mangrove – Processes

 

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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• Overview
• Inputs
• Processes
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Ammonia volatilisation

Ammonia volatilisation occurs in basic conditions and where concentrations of urea (derived from animals) are relatively high. In mangrove systems, ammonia volatilization is likely to be minor as soils are usually acidic (less than 7 pH)[1].

Anammox

Anammox can contribute to 3 to 10% of the total NO₃ loss in mangroves (6.1 (0-16) g/ha/day)^*[9]. The contribution of annamox is higher where oxygen concentrations are very low and soil carbon is high[9].

Biomass accumulation (vegetation)

Nitrogen in mangrove wetlands is accumulated in plant material through shrub and tree growth. Tree growth can accumulate between 21 (11-34) gN/ha/day^*[5].

Mineralisation (Decomposition/Ammonification)

Mineralisation in mangroves has been measured as fluxes of NH₄ and NO₃, with values of 15 ± 3 g/ha/day for NO₃[13]. These values are variable within seasons, but are especially sensitive to increases in N inputs, which can increase these rates 3-9-fold[13]. Ammonification is an important process in mangroves promoted by anaerobic soils[3].

Denitrification

Denitrification rates (912 (649-1,175) g/ha/day)^* are likely to be higher during flood events, when NO₃ concentrations increase. However, the proportion of NO₃ loss in the system due to denitrification could be higher in the dry season as a result of lower water flows[6][17]. Denitrification and anammox are likely to contribute to large NO₃ loss in mangrove forests[2].

Dissimilatory nitrate reduction to ammonium (DNRA)

DNRA is likely to be an important N pathway in mangroves[11]. The alternation between the two processes of DNRA and denitrification in mangroves could result in an input of NO₃ and an export of NH₄, especially during the dry season[6][17].  

Food chain transfer

Mangroves can sustain some coastal food chains (food webs), through the provision of N in the form of litter, algae growing on pneumatophores, or microbial biomass. The litter, algae and microbial biomass can be directly consumed by organisms within the mangroves, such as crabs or snails[16][15][7].

Immobilisation

Immobilisation (assimilation) in mangroves has been measured as fluxes of NH₄ and NO₃, with values of 44 (36-52) g/ha/day^* for NH₄[13]. These values are variable within seasons, and rates may increase similarly to those seen during mineralisation[13].

Nitrification

Nitrification is limited in mangrove wetlands as conditions in these wetlands are generally anoxic and acidic. If wetlands are polluted and soils become anaerobic (no oxygen), nitrification will not occur, and most N will be in reduced forms (e.g. NH₄)[12]. Nitrification is important for denitrification if N inputs are in the form of ammonium, as it transforms the N into the nitrate form required by denitrifying bacteria.

Nitrogen deposition from the atmosphere

Nitrogen can be deposited from the atmosphere to the biosphere as gas, dry deposition and precipitation. However, N deposition is only significant in areas with high industrial activity. In the Great Barrier Reef (GBR) catchments, N deposition is likely to be below 3 g/ha/day[4].

Nitrogen fixation from the atmosphere

Nitrogen fixation tends to be low in mangroves, especially in sites with high N inputs[14]. In Queensland, N fixation in mangroves has a mean value of 10 g/ha/day, with a range of values from zero to 33 g/ha/day with no clear seasonal pattern[6].

Sedimentation

Mangroves in general have high sedimentation rates. In the Herbert River, in the Great Barrier Reef region, sediments around mangrove forests typically accumulate 254 (11-337) g/ha/day^*[8]. Accumulation of sediment, and particulate N, tends to be higher in fringe forests of Rhizophora trees[10].

^*_{Nitrogen quantities are displayed as an average followed by a minimum and maximum (range), e.g. “average (min. of range - max. of range) units”.}

References

1. ^ Adame, Franklin, H, Rodriguez, S, Kavehei, E, Turschwell, M, Balcombe, SR, Burford, M & Ronan, M (2019), 'Nitrogen removal through denitrification by tropical forested wetlands', Marine and Freshwater Research, vol. 70, pp. 1513-1521.
2. ^ 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.
3. ^ Alongi, DM, Cycling and Global Fluxes of Nitrogen in Mangroves, p. 11.
4. ^ Beaulieu, JJ, Tank, JL, Hamilton, SK, Wollheim, WM, Hall, RO, Mulholland, PJ, Peterson, BJ, Ashkenas, LR, Cooper, LW, Dahm, CN, Dodds, WK, Grimm, NB, Johnson, SL, McDowell, WH, Poole, GC, Valett, HM, Arango, CP, Bernot, MJ, Burgin, AJ, Crenshaw, CL, Helton, AM, Johnson, LT, O'Brien, JM, Potter, JD, Sheibley, RW, Sobota, DJ & Thomas, SM (2011), 'Nitrous oxide emission from denitrification in stream and river networks', Proceedings of the National Academy of Sciences. [online], vol. 108, no. 1, pp. 214-219. Available at: http://www.pnas.org/cgi/doi/10.1073/pnas.1011464108.
5. ^ Boto, KG, Bunt, JS & Wellington, JT (September 1984), 'Variations in mangrove forest productivity in northern Australia and Papua New Guinea', Estuarine, Coastal and Shelf Science. [online], vol. 19, no. 3, pp. 321-329. Available at: https://linkinghub.elsevier.com/retrieve/pii/0272771484900283 [Accessed 3 November 2020].
6. ^ a b c Boto, KG & Robertson, AI (1990), 'The relationship between nitrogen fixation and tidal exports of nitrogen in a tropical mangrove system', Estuarine, Coastal and Shelf Science, vol. 31, pp. 531-540.
7. ^ Bouillon, S & Connolly, RM (2009), 'Carbon Exchange Among Tropical Coastal Ecosystems', in I Nagelkerken (ed.), Ecological Connectivity among Tropical Coastal Ecosystems. [online], Springer Netherlands, Dordrecht, pp. 45-70. Available at: http://link.springer.com/10.1007/978-90-481-2406-0_3 [Accessed 3 November 2020].
8. ^ Brunskill, GJ, Zagorskis, I & Pfitzner, J (2002), 'Carbon burial rates in sediments and a carbon mass balance for the Herbert River Region of the Great Barrier Reef Continental Shelf, North Queensland, Australia', Estuarine, Coastal and Shelf Science, vol. 54, pp. 677-700.
9. ^ a b Erler, D, Trott, L, Alongi, D & Eyre, B (25 March 2013), 'Denitrification, anammox and nitrate reduction in sediments of the southern Great Barrier Reef lagoon', Marine Ecology Progress Series. [online], vol. 478, pp. 57-70. Available at: http://www.int-res.com/abstracts/meps/v478/p57-70/ [Accessed 30 October 2020].
10. ^ Furukawa, K & Wolanski, E (1996), 'Sedimentation in mangrove forests', Mangroves and salt marshes, vol. 1, no. 1, pp. 3-10.
11. ^ Giblin, AE, Tobias, CR, Song, B, Weston, N, Banta, GT & Rivera-Monroy, VH (2013), 'The importance of dissimilatory nitrate reduction to ammonium (DNRA) in the nitrogen cycle of coastal ecosystems', Oceanography, vol. 26, no. 3, pp. 124-131.
12. ^ Mitsch, WJ & Gosselink, J (2015), Wetlands, p. 213, Wiley, New Jersey, USA.
13. ^ a b c d Molnar, N, Welsh, DT, Marchand, C, Deborde, J & Meziane, T (2013), 'Impacts of shrimp farm effluent on water quality, benthic metabolism and N-dynamics in a mangrove forest ( New Caledonia )', Estuarine, Coastal and Shelf Science. [online], vol. 117, no. 2, pp. 12-21. Available at: http://dx.doi.org/10.1016/j.ecss.2012.07.012.
14. ^ 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].
15. ^ Robertson, AI & Daniel, PA (1989), 'The influence of crabs on litter processing in high intertidal mangrove forests in tropical Australia', Oecologia, vol. 78, pp. 191-198.
16. ^ Sheaves, M & Molony, B (2000), 'Short-circuit in the mangrove food chain', Marine Ecology Progress Series. [online], vol. 199, pp. 97-109. Available at: http://www.int-res.com/abstracts/meps/v199/p97-109/ [Accessed 2 November 2020].
17. ^ 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.

Last updated: 31 July 2021