Seasonal variation of sedimentary nutrients and litter production in the mangrove ecosystem of indian sundarban: Implications for ecosystem dynamics

The objective of this research was to investigate the spatio-temporal variations in sedimentary nutrient levels and establish correlations with various hydro-geomorphic and ecological parameters, including the magnitude of tidal-inundation, distance from the river and sea-front, and litter production by different mangrove species within the study area.

Twelve transects were selected, each with atleast four sampling points spaced at intervals averaging 100 m, considering various hydro-geomorphic attributes for seasonal sediment sample collection. Eight major soil parameters were measured, including the nutrient parameters TN, TP, TK, OC, OM, NO₃^– and PO₄^3–, as well as CaCO₃. Mangrove litter collections were conducted using litter traps.

The total-nitrogen (TN) exhibited distinct patterns: the lowest annual mean was 152.24 ± 7.05 kg/ha in the lower zone, peaking at 209.7 ± 11.8 kg/ha in the middle zone, and decreasing in the upper zone with increasing distance from the sea. Along the ‘mangrove dominated intertidal mudflat’ gradient, TN was lower near the riverfront and higher in the forest interior. Seasonally, TN was highest in postmonsoon and lowest during the monsoon. Other parameters showed similar patterns with varying magnitudes. Litter production varied among species, with Excoecaria agallocha showed highest rate at 41.60 ± 9.58 g/m²/month, followed by Bruguiera gymnorrhiza and Avicennia alba. Litter production was highest in postmonsoon, declining towards the monsoon. ANOVA results revealed intricate relationships between seasons, transects, and the eight dependent variables.

The analysis underscored the pronounced spatio-temporal variability in nutrient levels, influenced by a range of hydro-geomorphic factors, and highlights a good correlation with litter productivity of the region.