**2. Materials and methods**

#### **2.1 Study area**

The study was conducted in Ijala-Ikeren wetland located within latitude 05.55°N and 05.57°N and longitude 05.68°E and 05.70°E in Warri, Delta State, Nigeria (**Figure 1**). The wetland is a brackish network of creeks and creeklets, and marshes with one or more relatively narrow connections to the sea.

The study area which covers a space of 1 km<sup>2</sup> was divided into 2 regions: interior region bearing three sites; site 1, 2 and 3, and edges (fringes) region bearing sites 4 and 5. Altogether, 5 sites were engaged. Site 1 is located at the position, 05.55940°N,

**Figure 1.** *Map of the study area.*

and 05.69630°E. The substratum here was covered with an admixture of black muddy and clayey sediment with an average depth of 0.2 m. Tidal flow was low and was at a low transparency. Vegetation here includes *Rhizophora racemosa*, *Rhizophora harrisonii* and *Rhizophora mangle.* This site is situated immediately after edges. Meanwhile, site 2 has the same substratum coverage and depth with site 1. The vegetation cover included thick stands of *Rhizophora racemosa*, *Rhizophora harrisonii* and *Avicennia africana.* The site is located at 05.44960°N and 05.69731°E. This site was very close to the oil pipelines. The last site in interior region; site 3, had the same substratum coverage and depth with sites 1 and 2. The vegetation cover were; *R. racemosa*, *R. harrisonii* and *Nymphaea lotus* (Water lily). The site is located at 05.55930°N and 05.69722°E. On the other hand, the two study sites representing the edges (fringes) region were sites 4 and 5. Site 4—the substratum was clayey with an average depth of 1.2 m, stagnant water with high infestation of invasive species such as water hyacinth (*Eichhornia crassipes*) most importantly. While at site 5—the substratum was clayey too with an average depth of <1 m. Stagnant water and some grasses occurred at this site. It was located at 05.55876°N and 05.69654°E. These sites (1–5) were selected on the strength of the tide and vegetation cover.

### **2.2 Environmental condition**

Physicochemical parameters such as air temperature, water temperature, and pH were determined in situ. Temperatures were measured using the 0–100°C mercury in glass thermometer (Kurison Model—59). The pH was determined in situ using digital pH meter (consort 121, Belgium) adopted from [23]. While, salinity was determined in the laboratory by using HACHCO150 Model for total dissolved solid/ conductivity/salinity meter.

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

## **2.3 Vegetation cover**

A description of the vegetation cover in and around the wetland was undertaken. Diversity of species of mangroves was recorded from the two studied regions. We used a [24] sampling technique for rapid assessment of the mangal vegetation of the brackish ecosystem in the study area by walking around at low tide. This involved a reconnaissance survey of the study stations of the Ijala-Ikeren mangrove ecosystem where a systematic sampling along the directed transects was applied to conduct the flora survey of the study sites.

## **2.4 Insect sampling**

Insect sampling was conducted in the dry season (October 2013—February, 2014) and in the wet season (March–June, 2014). It was a 9 month study. Collection of samples was carried out through the use of sweep and kicks nets, and hand collection. Access to the mangrove interiors was through Falcorp Mangrove Park. Hand collections were made from wetland (mangrove) plants and from ant hive (**Figure 2**). The sieve-like dip net was used to collect aquatic insects from a distance on the mangroves while small aquatic nets were used to collect specimens in the aquatic plant (*Nymphaea lotus* and Water lily) while in water. Specimens collected were placed in vials containing 70% ethanol solution (C2H6O).

Kick sampling method modified after [23] was used to collect aquatic insect larvae (macro-invertebrates) for 3 min. We used 1 min to conduct searches before disturbing the water column and placing the net against the direction of the current for actual sampling. This method was also used to collect insects from water surface, from boulders, logs of wood and plants (**Figure 3**). All the collected specimens were identified using keys of [25–27]. The identified specimens were counted and placed into vials of 70% ethanol (C2H6O) which were well labelled indicating the location and date of collection.

## **2.5 Amphibian fauna**

Sampling for amphibian was conducted using the Visual Acoustic Encounter Survey (VAES) method (i.e. listening to amphibians call and tracing the calls) at night and the anurans were captured by handpicking. The method was used along the trunk road (edges) traversing the area and in the interiors wetland (mangrove swamp) through the access to Falcorp Mangrove Park. Collection at the park was both during the day and at night.

### **2.6 Fish study**

We used empirical method to ascertain the occurrences and diversity of fish species within Ijala-Ikeren wetland from the local fishermen at a few fish landings therein. A few fish species were equally sighted, observed and noted in-situ.

#### **2.7 Statistical analysis of data**

Overall diversity of soil insect was expressed as species richness, abundance, evenness and Simpson diversity index. Species richness and diversity patterns are a fundamental point for any scientific act in conservation biology [28]. Species richness represents the simplicity of describing communities at different scales and its broadly understood meaning. The complementary picture of overall diversity pattern of any community was documented by information about the abundance of

#### **Figure 2.**

*An ant hive hanging on a mangrove plant in Ijala-Ikeren mangrove swamp where insect collection was made.*

**Figure 3.** *Insect collection from under woods, logs and fallen leaves in Ijala-Ikeren mangrove.*

species, the evenness of communities across the sampling region or the dominant species. Abundance is the kind of diversity measures that has inclusively been considered as equivalent to biodiversity per se [29] and referred to the sum of individuals in area. However, Simpson diversity index (D) is nearly the most tractable and statistically useful calculation [30]:

$$
\lambda = \Sigma p i^2,\\
D = \mathbf{1} - \lambda \tag{1}
$$

Where D is Simpson diversity index, λ is an index of dominance. pi is the proportion of the community occupied by the ith species.

All parameters of diversity were calculated with PAST (version. 1.92) software running on Windows® XP, [31].
