Palustrine

Palustrine – 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[4].

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Palustrine wetlands are considered hotspots of nutrient cycling due to their water logged and organic rich soils[11]. Nitrogen (N) can be transformed within palustrine wetlands through nitrification-denitrification, ammonification, mineralisation, immobilisation, biomass accumulation and sedimentation[11].

Anammox

Anammox (anaerobic ammonia oxidation) is likely to be a minor process in palustrine wetlands[9][14].

Biomass accumulation (vegetation)

Nitrogen in palustrine wetlands is accumulated in plant material (biomass), through grass, herb, sedge, shrub, aquatic vegetation, and tree growth. Tree growth can accumulate around 211 (38-638) gN/ha/day^*[2]. Grass accumulates about 7 gN/ha/day[2], but most of this N will return to the soil when the plant dies and is rapidly decomposed. Higher nitrogen accumulation as plant biomass will occur in palustrine wetlands with warm and wet conditions, and in areas with excessive weeds[2]. After dying, the macrophytes (including invasive weeds) will release N, which they have stored in their tissue[10].

Mineralisation (Decomposition/Ammonification)

Decomposition in most palustrine wetlands, especially in deep soils (greater than 10 cm), is likely to be low due to the waterlogged and anoxic conditions, low pH, and toxic compounds of Melaleuca leaves[12]. Soils in palustrine wetlands have carbon:nitrogen ratios of around 14:1, suggesting that surface soils have favourable conditions for organic matter decomposition[2] which would result in NH₄ production and a build-up of N in the soil due to mineralisation[5]. Deeper soils have conditions that favour accumulation of nitrogen.

Denitrification

Denitrification in palustrine wetlands is usually high compared to other land types and is associated with the amount of nitrate available[1]. Denitrification in palustrine wetlands is also higher in soils rich in carbon (generally more than 5%), when temperature is between 20-30˚C and soil redox is between -100 to 200 mv[11]. Denitrification can account for 64-70% (1,200 (384-2328) g/ha/day)^*[1] of N removal from palustrine wetlands. Export of nitrogen as N₂ gas is likely to occur as a result of incomplete denitrification and nitrification processes, and typically accounts for less than 1% of nitrogen transformed by denitrification[4].

Food chain transfer

In forested palustrine wetlands, light limitation and a source of carbon (e.g. Melaleuca or Eucalyptus leaves), which are toxic to most organisms, could mean relatively low transfers of N through the food chain (food web). In grass/sedge palustrine wetlands, epiphyton – especially if dominated by diatoms – could be transferred through the food web into insect, fish and bird biomass[8]. Palustrine wetlands that are frequently flooded have higher N transfer through the food chain as animals move into these wetlands to feed during the wet season[8].

Nitrification

Nitrification is limited in palustrine wetlands as they are generally anoxic and acidic (low pH). 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)[11]. 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 as an oxygen source.

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[13]. In the Great Barrier Reef catchments, N deposition is likely to be below 3 g/ha/day^*[13].

Nitrogen fixation from the atmosphere

Nitrogen fixation from the atmosphere is highly spatially and temporally variable in wetlands. This fixation tends to be low at a rate of 44 (11-77) g/ha/day^*, especially in sites where N inputs are high, such as in many wetlands within the Great Barrier Reef catchments[7]. N fixation tends to be high where macrophytes (aquatic plants) are present and nitrogen is limited[7].

Sedimentation

Palustrine wetlands usually receive sporadic amounts of sediment, especially during large floods. Nitrogen accumulated in the sediments of palustrine wetlands can be high in areas associated with large suspended sediment input loads, long residence times, and slow water flows[6]. Rates of sedimentation in palustrine wetlands are 39 (38-45) g/ha/day^* or about one millimetre per year in floodplain wetlands in some catchments of the Great Barrier Reef[3].

Ammonia volatilisation

Ammonia volatilisation occurs in basic conditions (higher than pH 8) and where concentrations of urea (derived from animals) are relatively high[13]. In palustrine wetlands, ammonia volatilization is likely to be minor (< 1 g/ha/day) as soils are usually acidic (less than 6 pH)[2].

^*_{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. ^ a b 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. ^ a b c d e Adame, MF, Reef, R, Wong, VNL, Balcombe, SR, Turschwell, MP, Kavehei, E, Rodríguez, DC, Kelleway, JJ, Masque, P & Ronan, M (2020), 'Carbon and nitrogen sequestration of Melaleuca floodplain wetlands in tropical Australia', Ecosystems. [online], vol. doi.org/10. Available at: https://link.springer.com/article/10.1007%2Fs10021-019-00414-5.
3. ^ Adame, MF, Reef, R, Wong, V, Kavehei, E, Rodriguez, D, Kellaway, J, Masque, P & Ronan, M (2020), 'Carbon and Nitrogen Sequestration of Melaleuca Floodplain Wetlands in Tropical Australia', Ecosystems, vol. 23, pp. 454-466.
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. ^ Fernex, F, Bernat, M & Ballestra, S (1992), 'Ammonification rates and 210Pb in sediments from a lagoon under a wet tropical climate : Marica , Rio de Janeiro state , Brazil', Hydrobiologia, vol. 242, pp. 69-76.
6. ^ Gell, P, Fluin, J, Tibby, J, Hancock, G, Harrison, J, Zawadzki, A, Haynes, D, Khanum, S, Little, F & Walsh, B (July 2009), 'Anthropogenic acceleration of sediment accretion in lowland floodplain wetlands, Murray–Darling Basin, Australia', Geomorphology. [online], vol. 108, no. 1-2, pp. 122-126. Available at: https://linkinghub.elsevier.com/retrieve/pii/S0169555X09000397 [Accessed 2 November 2020].
7. ^ a b Howarth, RW, Marino, R, Lane, J & Cole, JJ (1988), 'Nitrogen fixation in freshwater, estuarine, and marine ecosystems. 1. Rates and importance', Limnology and Oceanography, vol. 33, pp. 669-687.
8. ^ a b Jardine, TD, Pusey, BJ, Hamilton, SK, Pettit, NE, Davies, PM, Douglas, MM, Sinnamon, V, Halliday, IA & Bunn, SE (2012), 'Fish mediate high food web connectivity in the lower reaches of a tropical floodplain river', Oecologia, vol. 168, pp. 829-838.
9. ^ Jetten, MSM, Strous, M, van, P, Schalk, J, van Dongen, UGJM, van, G, Logemann, S, Muyzer, G, van Loosdrecht, MCM & Kuenen, JG (1998), 'The anaerobic oxidation of ammonium', FEMS microbiology reviews, vol. 22, pp. 421-437.
10. ^ Lu, J, Bunn, SE & Burford, MA (May 2018), 'Nutrient release and uptake by littoral macrophytes during water level fluctuations', Science of The Total Environment. [online], vol. 622-623, pp. 29-40. Available at: https://linkinghub.elsevier.com/retrieve/pii/S0048969717332576 [Accessed 2 November 2020].
11. ^ a b c d Mitsch, WJ & Gosselink, J (2015), Wetlands, p. 213, Wiley, New Jersey, USA.
12. ^ Nielsen, LP, Enrich-Prast, A & Esteves, FA (2004), 'Pathways of organic matter mineralization and nitrogen regeneration in the sediment of five tropical lakes', Acta Limnol Bras., vol. 16, no. 2, pp. 193-202.
13. ^ a b c Phoenix, GK, Hicks, W, Cinderby, S, Kuylenstierna, J, Stock, W, Dentener, F, Giller, K, Austin, A, Lefroy, R, Gimeno, B, Ashmore, M & Ineson, P (2006), 'Atmospheric nitrogen deposition in world biodiversity hotspots: the need for a greater global perspective in assessing N deposition impacts', Global Change Biology, vol. 12, pp. 470-476.
14. ^ Tao & Wang (2009), 'Effects of vegetation, limestone and aeration on nitrification, anammox and denitrification in wetland treatment systems', Ecological Engineering, vol. 35, pp. 836-842.

Last updated: 31 July 2021