Effect of pollution and seasonal changes on litter fall and accumulation in Mangrove Forest (Rhizophora Species) of the Niger Delta, Nigeria

Abstract

Background and Objective: Hydrocarbon pollution and seasonal changes cause defoliation and litter fall, respectively. It is hypothesized that increasing pollution and rapid seasonal changes can cause increased litter fall. The objectives of the study were (1) To determine the annual litter fall of leaves, fruits and flowers, (2) To determine the total litter accumulation and (3) To determine the amount of litter fall in wet and dry season in highly and lowly polluted treatments. Materials and Methods: Litter fall data were collected monthly for three years at four 20×20 m plots in highly and lowly polluted plots and locations in the mangrove forests. A total of 1,440 litter samples were collected from litter traps randomly placed under mangrove trees. The litters were sorted into leaves, fruits and flowers. Results: There is a negative correlation between precipitation and litter fall (leaf r = − 0.68, fruit r = − 0.47, flower r = 0.31). Mean-monthly litter fall for leaves, fruits and flowers were 23.9±1.3, 9.3±0.8 and 2.8±0.6 g m–2/year, respectively. Total average litter fall was 66.5% leaf, 25.5% fruit and 8% flower. Total litter fall between locations and amongst plots did not vary significantly (p>0.05). But the 3 years cumulative litter fall was higher in highly polluted treatment (~4777 g m–2/year) than in lowly polluted treatment (4077 g m–2/year). Precipitation and season significantly influenced litter fall (p<0.0001). Dry season (November-January) had higher litter fall than wet season (February-October). Conclusion: This implies that pollution and season influence the rate of litter fall.