Abstract
Mangroves are habitat specific and grow mainly in swampy soil, but due to anthropogenic activities (e.g. sand mining) other species had encroached into their habitat. It is thus hypothesized that change in species diversity will lead to change in soil chemistry. In a 40 m × 90 m plot, diversity index (H) and importance value (Iv) of weed were estimated. Soil and weed samples were collected and analyzed for total hydrocarbon content (THC), Zinc (Zn), Lead (Pb) and Cadmium (Cd). All samples were analyzed with atomic absorption spectrophotometric method using the HACH DR 890 calorimeter (wavelength 420 nm). The result shows that swampy soils were more acidic (3.1 - 3.5) than sandy soils (4.2 - 4.7). Swampy soil was also more saline and thus has higher conductivity (8320 - 9880 μS/cm) than sandy soil (4320 - 5650 μS/cm). Mangrove swamp had higher total organic carbon (TOC) (2.25% - 3.41%) than sandy soil (0.12% - 0.21%). There was a significant difference in THC and heavy metals in soil (F8,63 = 2.04, P 8,63 = 247.0, P > 0.05). Concentration of THC and heavy metal was higher in plant than in soil. Reissantia indica, an aquatic weed, had the highest concentration of THC in root soil. A total of fifteen (15) weed species were identified, out of which Mariscus longibracteatus had the highest diversity (-0.366) followed by Mariscus ligularis (-0.339) and Paspalum vaginatum (-0.270). Similarly, M. longibracteatus had the highest importance value in the study site (Iv = 58.24). This result implies that the presence of weed species in mangrove forest is an indicator of human disturbance of the ecosystem. It also means that the weeds were bioaccumulating THC and heavy metals present in the soil.
Highlights
Mangroves are habitat specific and inhabit swampy and saline environment [1] [2] [3] [4]
There was a significant difference in total hydrocarbon content (THC) and heavy metals in soil (F8,63 = 2.04, P < 0.05), but there was no significant difference in THC and heavy metals in plant species (F8,63 = 247.0, P > 0.05)
This study is aimed at investigating the diversity of weed and other plant species found in sand filled mangrove forests, and to determine the concentration of some heavy metals in soil and plant
Summary
Mangroves are habitat specific and inhabit swampy and saline environment [1] [2] [3] [4]. The weed species are able to grow at the fringes and perimeters of the mangrove forest that had been cut down for the purpose of creating access way for pipelines [11]. This is because the pipeline route is usually covered with sandy soils brought elsewhere, which further introduce and accelerate weed growth [12]. This study is aimed at investigating the diversity of weed and other plant species found in sand filled mangrove forests, and to determine the concentration of some heavy metals in soil and plant. The objectives of this study are: 1) to determine the diversity index (H) and importance value (Iv) of the weed species 2) to determine the THC and heavy metal concentration in both soil and plant, and 3) to compare the THC and heavy metal concentration in plant and soil
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