Carbon credits assessment in a mixed mangrove forest vegetation of Cross River Estuary, Nigeria

The relative contributions of a mixed mangrove forest vegetation comprising Nypa fruticans Wurmb. Arecaceae, Rhizophora racemosa GFW May. Rhizophoraceae, Avicennia germinans var. africana P. Beauv. Avicenniaceae) of the Great Kwa River, in the Cross River estuary were studied. Litter production and composition along tidal gradients (low, mid, high) were measured over a 12 month period using litter traps. The average monthly litterfall was 37.43g dwt m-2 (~ 449.2g m-2 y-1). Leaves constituted 64%, wood 13% and “miscellaneous” litter (propagules and stipules) 23%. The average monthly litter biomass on the forest floor was 13.38g dwt m-2 (~160.56gm-2y-1). This constituted 35.75% of the litter produced. Litterfall and litter biomass varied significantly (P<0.001) temporally and spatially (across tidal gradients). The average monthly litterfall at low, mid and high tide levels were 21.90, 42.80 and 47.53 (g dwt m-2) with leaf litter constituting 58, 64 and 65%, wood litter 18, 15 and 12% and “miscellaneous” litter 26, 21 and 23% respectively. Similarly litter biomass was 7.43, 16.08 and 16.72 (g dwt m-2) with leaf constituting 56, 65 and 64%, wood litter 21, 15 and 13% and “miscellaneous” litter 23, 20 and 23% respectively. Litterfall and litter biomass were observed to exhibit seasonality. Litterfall had bimodal response peaking during rainy (August) and dry (February) season while litter biomass was low during the rainy season (June to September). Litterfall and litter biomass increased generally across tidal gradients towards the high tide level. The periodicity, amount and fate of litter in this mixed mangrove forests have implications in the understanding and prediction of patterns of accumulation and distribution of mangrove litter. This provides insight into carbon storage potentials of the mangrove ecosystems in Nigeria.

Author(s): Edu EA, Nsirim LEW, Ononyume MO and Nkang AE

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