**4. Discussion**

The study of vegetation in Ijala-Ikeren wetland clarified the richness of mangrove species, which is covered by about 95% Rhizophora species (red mangrove)

## *Impact of Disturbances on the Biodiversity of Ijala-Ikeren Wetland Ecosystem in Niger Delta DOI: http://dx.doi.org/10.5772/intechopen.82604*

and *Avicennia africana* (white mangrove) with 5% other species, mostly *Pandamus candelabrum* and *Eichhornia crassipes*. This vegetation community richness of biotic community is more present and stable [32]. The complete absence of Ephemeroptera, Diptera, Odonata, Coleoptera, Trichoptera and Arachnida especially mesofauna were observed which may be due to the brackish water predominantly. A significant change was also detected in the environmental condition with particular reference to pH value, which was estimated at between 6.3 in 2009 and decreased to 4.8 on the average (acidic value). This may be attributed to the absence of the above listed arthropod orders especially as insects cannot tolerate the slightest change in salinity values beyond the fresh water concentration. This same scenario could be playing out for the amphibians, as none were recorded or encountered in the wetland (within the mangroves). This phenomenon has certainly explained the very low occurrence of species diversity of insects and amphibians populations and occurrences in the wetland ecosystems. This is particular for insects, as no aquatic insect larvae were encountered or collected during the survey period. Similarly, no amphibian eggs/tadpoles or adult forms were encountered inside the mangrove habitats of Ijala-Ikeren wetland.

The acidity of water was explained by [6] who investigated the impact of refinery effluents around Warri Refinery and Petrochemical Company (WRPC) on surface waters of the creeks and soil qualities of host communities within and around Ijala-Ikeren wetland, and concluded the change in water pH to be 6.3, while the soil pH was 6.8 in Ijala-Ikeren wetland. This inference may be related to the discharge of these effluents from Warri Refinery and Petrochemical Company (WRPC) into Warri River which feeds the Ijala waters and also crude oil and its fraction seepages from numerous loading and off-loading jetties within the river which finds its way into the creeks in the Ijala-Ikeren wetland. They further stated that the Warri River is open to flooding which carries various contaminants. Contrary to our findings in water pH, the sediments studies conducted elsewhere in the Mexican pacific and Thailand, recorded alkaline pH values ranging from 6.91 to 7.83 [18, 22].

Secondly, the discovery of illegal toxic waste dumpsites belonging to WRPC within these wetlands (pers. comm.) could increase the pollutant load of the study area. In turn, the highest concentration of calcium and salinity level was reported at the surface water within the wetland as reported by [6] though we did not analyse for calcium and heavy metals in this study. Also, heavy metals in varying concentrations and reasonable quantity from refinery effluents that resulted from Nigeria's crude oil could be one of the contributing factors to the acidic pH values. Especially, the metallic components in crude oil which are in the form of metalloporphyrin chelates, transition metal complexes, organometallic compounds, carbonyl acid salts of polar functional groups and colloidal minerals while other inorganic constituents of crude oil are sulphur, nitrogen, and oxygen [33].

Spatially, the study sites at the mangrove swamp was the richest habitat in terms of species number of insects, site 1 had the greatest value in Margalef 's species richness index (d) and diversity of species out of these sites. This result may relate to increasing the renewal of water during high tide as a common phenomenon in the area which could give rise to runoffs of debris from land into the mangrove. On the other hand, site 2 had the least value of both indices. As expected, this study site was characterised by its proximity to oil pipelines which over time had ruptured severely due to vandalisation and outlet that leads into the creeks.

Among the sampled insects, the presence of *Chironomus* sp. and *Aquarius remigis* at low salinity (<2 ppm) and acidic pH of surface water were detected. *Chironomus* sp. (Dipteran-Chironomidae) is tolerant of polluted water and an indicator of poor water quality with reduced oxygen concentration, and unhealthy ecosystem [34, 35]. Therefore, this is a clear indication of the effect of the effluent on the biotic components of the water ecosystem.

Many amphibian species and their eggs are unable to tolerate and thrive in the brackish/salty environments of the mangrove (interior). One species, *H. occipitalis* was however an exception; this frog was encountered in several stagnant pools of water along the earth road leading to the wetland. Some individuals of this frog were sighted in a backhouse pond (edge) sharing boundary with the Ijala-Ikeren mangrove wetland.

So, the presence of *Aquarius remigis* and amphibian species; *Hoplobatrachus occipitalis,* at pH value of 4.1–4.9 indicates that the two species are indicator species of high acidic pH value. Those species whose presence occurred in acidic water bodies are tolerant of such environment and could be good candidate for monitoring changes in pH values in aquatic ecosystem especially brackish water including mangrove swamps. In accordance with the record of [36] these species of frog were found in some Nigerian waters at lower pH value which ranged from 4.1 to 4.2.

The presence of the insect (*Chironomus* sp.) and amphibians (*Hyperolius concolor*, *H. burtoni*, *H. guttulatus* and two unidentified *Hyperolius* species of *Afrixalus dorsalis*, *A. fulvovitattus* and *Afrixalus* sp.) are indicators of high levels of contamination of water from petroleum refinery effluents, however, we did not analyse the content of the effluent. They are indicators of acidic water of pH value between 5.3 and 6.1. In addition, the absence of aquatic insects in the adjacent mangrove swamps within Ijala-Ikeren wetlands tells us of the high level of contamination trends in the mangrove and creeks/creeklets in the area which may have generally affected the density of fish catch (outside overfishing, and using the wrong fishing gears) in the area which is a major source of livelihood for the host communities (personal communication). This invariably has affected the income of the people and also their protein intake. Despite the diversity of fish fauna (20 individual species), the fishermen remarked that the population of fish per catch is fast dwindling a situation they attributed to human induced factor rather than natural. [23] asserted that fish and crustaceans species are well supported in an alkaline pH value of water greater than 7. Furthermore, the absence of amphibians in the mangrove equally raises concern as amphibians have important roles to play within nature and their sensitivity to changing environmental conditions may help determine the health of an ecosystem.

Species richness measures the number of different kinds of species present in a particular area. Margalef 's Species Richness index (d) values range from 1 to 5 where the higher index indicates the greater diversity (**Table 3**). Shannon diversity index (H′) takes into account the number of species and the evenness of the species. Diversity (H′) values less than 1.0 are considered very low; between 1.0 and 3.0 have moderate diversity, while any value greater than 3.0 signifies high diversity and ecosystem stability (i.e. similar to a pristine ecosystem). Evenness (E′) refers to how evenly each species is represented in a given ecosystem. Equitability assumes a value between 0 and 1 with 1 being complete evenness.

The abundance was very evident in the order Hymenopteran (*Formica* sp.) (Appendix, **Figure A2**). These could be adduced to the fact that most arboreal ants are at least partially herbivorous—feeding on extra-floral nectaries, food bodies, pollen, epiphylls, and sap. They are also cryptic herbivores that feed on hemipteran honeydew [21, 37, 38].
