TITLE:
Diversity and Chemical Composition of Weeds in Sand-Filled Mangrove Forest at Eagle Island, Niger Delta, Nigeria
AUTHORS:
Aroloye Ofo Numbere
KEYWORDS:
Heavy Metals, Mangrove Weed, Soil, Species Diversity, Sand Fill, Swamp
JOURNAL NAME:
American Journal of Plant Sciences,
Vol.11 No.7,
July
13,
2020
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.