PARENT SESSION
Contributed Oral Session 83: Human Impacts on Coastal Areas
Wednesday, August 10, 8:00 AM - 11:30 AM, Meeting Room 520 A, Level 5, Palais des congrès de Montréal

Fate of nitrogen in mangrove wetland.

TAM, Nora F.Y.^*,, Wong, A.H.Y., Wong, Y.S.,

ABSTRACT- A series of computer-controlled mangrove tide tanks planted with 3 years-old Kandelia candel was constructed to investigate the fate of ammonium-nitrogen under two tidal regimes: (i) 12 hour wet/12 hour dry (a long tidal regime) and (ii) 6 hour wet/6 hour dry/6 hour wet/ 6 hour dry daily (a short tidal regime). All tanks were irrigated with ¹⁴NH₄Cl solution for six water cycles (each cycle lasted for five weeks) at an amount of 1.8 g per tank per cycle, followed by the addition of ¹⁵NH₄Cl stable isotope in the same amount for another three cycles. During the experiment, TKN (total Kjeldahl nitrogen) and inorganic N (NH₄⁺-, NO₂^--, and NO₃^--N) were never detected in the tidal water, suggesting that the added NH₄⁺-N was successfully removed by the mangrove system. The added NH₄⁺-N did not accumulate in the sediments but algal and plant growth was promoted with more nitrogen assimilation. The most obvious changes were the increases in numbers of ammonium oxidizers, nitrite oxidizers and denitrifiers in surface sediments (0-2cm), indicating that microbial nitrogen transformation was accelerated and more nitrogen was left the ecosystem via nitrogen gas. The mangrove system received a short tidal regime had higher numbers of nitrifiers and lower ammonium, on the contrary, significant higher populations of denitrifiers and lower nitrate were found in sediments receiving a long tidal regime.

Key words: mangrove, ammonium, nitrification, denitrification