Lacustrine

Lacustrine – 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[2].

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Lacustrine wetlands (lakes) have the largest water to soil ratio of all the wetlands and are dominated by aquatic transformations of nitrogen in aerobic conditions, e.g. in surface waters.

Ammonia volatilisation

Ammonia volatilisation occurs in basic conditions (higher than pH 8) and where concentrations of urea (derived from animals) are relatively high[15].

Anammox

Anammox (anaerobic ammonia oxidation) is likely to be a minor process in lakes[9][16].

Biomass accumulation (vegetation)

Nitrogen in lakes can be accumulated as macrophytes. These macrophytes may uptake approximately 58 (46-70) g of N per day[1], but most of this nitrogen will return to the soil/sediment when the plants die[11] or are consumed by animals. Areas of excessive weed growth may be an indication of high nitrogen accumulation[12].

Mineralisation (Decomposition/Ammonification)

In the littoral zone, where macrophytes can be abundant, decomposition can be high during periods of low water levels[11].  After dying, the macrophytes (including invasive weeds) will release N, which they have stored in their tissue[11]. In open water, algal or macrophyte blooms can produce high volumes of organic matter that can be deposited in the bottom of the lake, where some of it can be decomposed and some stored (i.e. recalcitrant matter not broken down).

Ammonification proceeds slowly in anaerobic environments, but it can be high in tropical lakes due to high temperatures that allow fast nutrient cycling[10].

Denitrification

Denitrification in lakes is likely to be highest in areas of the lake with abundant macrophytes[2] (410 (230-592) g/ha/day), and in lake sediments, where carbon is abundant, and where nitrate is available. Lower rates of denitrification typically occur in areas of open water[16]. Denitrification can also occur under floating macrophyte beds (including weed mats), however, if the weed mats are too dense the conditions can become too anoxic for denitrification to occur[4].

Food chain transfer

Lacustrine wetlands are likely to have high N transfers through the food chain (food web), especially in sites where epiphyton or phytoplankton are abundant[8]. Epiphyton are most abundant where macrophytes with complex structures occur in shallow areas of lakes[14]. Lakes connected to coastal waterways, are hotspots for N consumption by resident or migratory animals[8], especially where diatoms, an important source of nutrition for animals, are abundant.

Nitrification

Nitrification is likely to occur in areas around the edge of the lake where macrophytes are abundant, but not where they are so dense that conditions are anoxic[13][16][2].

Nitrogen deposition from the atmosphere

Nitrogen can be deposited from the atmosphere to the biosphere as gas, dry deposition and aerosol particles entrained in rain or other precipitation. However, N deposition is only significant in areas with high industrial activity[15]. In the Great Barrier Reef catchments, N deposition is likely to be less than 3 g/ha/day[15].

Nitrogen fixation from the atmosphere

In surface waters, nitrogen (N) fixation can be significant (40 (8-71) g/ha/day)^*. The fixation process can be enhanced:

• in areas/sites with limited N
• by the presence of macrophytes
• during N-fixing cyanobacteria blooms[7].

Sedimentation

Lakes can receive sporadic, but large amounts of sediment with associated particulate N, especially during large floods. Nitrogen accumulated in the sediment (217 (7-321) g/ha/day)^* will be higher in areas with large suspended sediment loads and long residence times[5]. At the central, deeper area of lakes, sediment can accumulate in large quantities, typically at rates of 1-2 mm/yr[3][6].

Excess sediment can fill up lakes leading to the loss of the lake and associated values and services.

^*_{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, M, Pettit, N, Valdez, D, Ward, D, Burford, M & Bunn, S (2017), 'The contribution of epiphyton to the primary production of tropical floodplain wetlands', Biotropica, vol. 49, pp. 461-471.
2. ^ a b Adame, MF, Waltham, NJ, Iram, N, Farahani, BS, Salinas, C, Burford, M & Ronan, M (8 July 2021), 'Denitrification within the sediments and epiphyton of tropical macrophyte stands', Inland Waters. [online], pp. 1-10. Available at: https://www.tandfonline.com/doi/full/10.1080/20442041.2021.1902214 [Accessed 31 July 2021].
3. ^ Carnell, PE, Masque, P, Windecker, SM, Brenker, M, Baldock, J, Brunt, K & Macreadie, PI (2018), 'Carbon stocks, sequestration, and emissions of wetlands in south eastern Australia', Global Change Biology, pp. 1-12.
4. ^ Cary, PR & Weerts, PGJ (June 1983), 'Growth of Salvinia molesta as affected by water temperature and nutrition I. Effects of nitrogen level and nitrogen compounds', Aquatic Botany. [online], vol. 16, no. 2, pp. 163-172. Available at: https://linkinghub.elsevier.com/retrieve/pii/0304377083900918 [Accessed 2 November 2020].
5. ^ 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].
6. ^ Haberle, SG (2018), 'A 23,000-yr pollen record from Lake Euramoo, Wet Tropics of NE Queensland, Australia', Quaternary Research, vol. 64, no. 2005, pp. 343-356.
7. ^ 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. ^ Lewis, WM (1996), 'Tropical lakes : how latitude makes a difference', Perspectives in Tropical Limnology, p. 43, SPB Academic Publishing, Amsterdam, The Netherlands, eds. F Schiemer & K T Boland.
11. ^ a b c Lu, J, Bunn, SE & Burford, MA (2018), 'Effects of water level fluctuations on nitrogen dynamics in littoral macrophytes', Limnology and Oceanography, vol. 63, no. 2, pp. 833-845.
12. ^ Mitsch, WJ & Gosselink, J (2015), Wetlands, p. 213, Wiley, New Jersey, USA.
13. ^ 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.
14. ^ Pettit, NE, Jardine, T, Hamilton, SK, Sinnamon, V, Valdez, D, Davies, PM, Douglas, MM & Bunn, S (2012), 'Seasonal changes in water quality and macrophytes and the impact of cattle on tropical floodplain waterholes', Marine and Freshwater Research, no. 66, p. 788.
15. ^ 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.
16. ^ a b c 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: 2 August 2021