Impact of hydrocarbon pollution on the mangrove ecosystem of the Niger River Delta, Nigeria.

摘要

Mangroves are habitat specialists found in the interface between the land and the sea. They have a complex relationship with organisms in their surroundings. They are global biodiversity hotspot, carbon sink and purifiers of the environment. They are used to produce some useful by-products e.g. hats, mats, herbs, building materials and food. This dissertation provides a multi-dimensional approach in studying the effect of hydrocarbon pollution in light of the steady state mangrove dynamics. This theory postulates that mangrove is in a steady state no matter the type of disturbances it experiences. This study was done in the mangroves of the Niger River Delta, Nigeria, an oil rich area. It looked at the effects of hydrocarbon pollution on productivity using the productivity-biomass framework. A three-year productivity study was done using traps to collect litters in plots with different pollution gradients. Results showed that highly polluted plots had higher productivity than lowly polluted plots, which is attributed to an adaptive mechanism by the mangrove to shed off its toxic leaves. The ratio of productivity (P) to biomass (B) was used to determine whether the mangroves were in a steady or successional state. Values in Okrika, a highly polluted system was lower than that in Buguma. This indicates that the former was more stable than the later. Deforestation of a large section of the forests in Buguma, resulted to the high (P/B) ratio. This finding therefore indicates that mangroves can survive serious hydrocarbon pollution, but will not survive a complete deforestation. Herbivory is also a significant aspect of the mangroves ecosystem. The West African red mangrove crabs (Goniopsis pelii) were the major cause of herbivory by their consumption of over 50% of the leaves. Neither hydrocarbon pollution nor age of leaves deterred the crabs from feeding on the leaves. However, hydrocarbon pollution had some effect on the growth of mangrove propagules and Nypa palm seedlings in a common garden experiment. Concerning survival, seedlings in lowly polluted soil survived longer than seedlings from highly polluted soil whereas, Nypa palms, the major exotic species exhibited higher survival ability than the mangroves at different pollution gradient.