DISTRIBUTION OF PHOSPHORUS POOL IN UTTAN MANGROVES, MAHARASHTRA, INDIA
Phosphorus is an important limiting nutrient and affects mangrove ecosystem significantly. The dynamics of phosphorusin the mangrove ecosystem in Uttan along Gorai-Manori creek, Maharashtra was studied during the post-monsoon period to assess the distribution of phosphorus (P) in the water, sediments and mangroves. Water, sediment, leaf and litter fall samples were collected fortnightly during the study period. P fractionated by sequential extraction from bulk, and rhizospheric sediments of A. marina and B. cylindrica were compared. The internal P loading through litter-fall of A. marina and B. cylindrica were also investigated.
The average reactive and total P level of water was found to be 0.06 mg. l-1 and 0.63 mg. l-1 respectively. Total P in the sediment of the study site was 1440.04, 1569.28 and 1551.27 mg. kg-1 in bulk, rhizospheric sediments of A. marina and B. cylindrica respectively. Organic P was dominant in all sediments. The P fractions did not differ significantly among sediments except NaHCO3-total P and HCl-total P which indicated the significant rhizospheric effect on the distribution and speciation of P in the mangrove sediments studied. The rhizospheric sediment of A. marina had significantly higher labile-P than bulk sediment. The percentage of labile phosphorus was in the following order: rhizospheric sediment of A. marina (28.75%) > B. cylindrica(25.19%)>bulk sediment (22.5%).The rhizospheric sediment of B. cylindrica had significantly more of moderately-labile-P and non-labile-P than other sediments. Based on bioavailability, the P fractions were in the order: moderately-labile P > non-labile P > labile P in all the sediments. The aggregate of fractions based on bioavailability was significantly different than the individual fractions between rhizosphere and non-rhizosphere sediments. This might be due to the qualitative and quantitative difference in root exudates as well as the diffusion characteristics of root exudates from rhizosphere to bulk sediment. The matured leaves as well as leaf-litter of A. marina had significantly higher P than that of B. cylindrica. The P in matured leaves of A. marina varied from 1502.79 - 1968.27 mg. kg-1 and in B. cylindrica, it varied from 1176.78- 1349.37 mg. kg-1. The leaf-litter of A. marina (1055.61 mg. kg-1) had significantly higher P than that of B. cylindrica, (881.28 mg. kg-1). A. marina and B. cylindrica contributed 13.88 and 7.50 mg P. m-2. month-1 load to the ecosystem through litter-fall, respectively.
