POTENTIAL OF NITRIFICATION RATE IN SEDIMENTS OF GREY MANGROVE (AVICENNIA MARINA) LOCATED AT DIFFERENT STATIONS ALONG KARACHI COAST, PAKISTAN

Mangrove acts as a vital source/sink pool for biogeochemical processes (nitrogen cycle) in the ecosystem. Owing to the importance of nitrification process in mangrove sediments the present study was undertaken to assess seasonal variation in potential nitrification (PN) rate in the mangroves along the Karachi coast. Sediments samples were retrieved in triplicate from the rhizosphere at four sites during pre-monsoon, monsoon, and post-monsoon season and divided into the top, middle, and bottom (3 cm each) of the core. Overall, the potential nitrification rate was high in the post-monsoon season as compared to pre-monsoon season and monsoon season. In terms of sections of sediment cores, PN rate was high in the middle and bottom sections as compared to the top section. Among sites, at Sandspit and Korangi Creek, the highest PN rate was observed in the middle section of the sediment at 45mM and 15mM chlorate concentrations at 6 hours of incubation. However, at Manora Channel and Port Qasim, it was found high in the bottom section at 60mM and 15mM at 6 hrs. of incubation, respectively. A distinct seasonal variation in Physico-chemical variables including temperature, salinity, pH, and dissolved oxygen was observed at all four stations. In the case of nutrients ion, the highest value of NO2 was observed in pre-monsoon, and NO3 and PO4 ions were in post-monsoon season at all stations. While the maximum value of NH4 ion was recorded in pre-monsoon followed by post-monsoon and monsoon seasons. In conclusion, the present study revealed a strong potential nitrification phenomenon observed at all stations with a slight variation that may be due to the relevance of anthropogenic activities along the backwaters of the Karachi coast.