Aroloye O. Numbere

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Plastic pollution has become a global problem with the proliferation many plastic goods. This study thus hypothesized that accumulated plastic waste will have adverse effect on mangrove growth. The study was carried out at a sand-filled and deforested mangrove forest at Eagle Island. Ten soils samples each (n =20) were collected underneath accumulated plastic waste vertically and horizontally. The soils were put in polythene bags and sent to the laboratory for analysis of total hydrocarbon content (THC), and heavy metals i.e., Zinc (Zn), Lead (Pb) and Cadmium (Cd) using the HACH DR 890 colorimeter (wavelength 420 nm) and microwave accelerated reaction system (MARS Xpress, North Carolina) respectively. In addition, mangrove (Rhizophora species) seedlings were also collected with soils from the plastic waste and non-plastic waste sites (control). The result shows that there is no significant difference in heavy metal concentration along the profile i.e., surface, and sub-surface soils (F1, 30 = 1.83, P = 0.186), and soil gradients (F3, 28 = 0.60, P = 0.619) of the soil. In contrast, there is significant difference in seedling growth between the control and plastic soils (F4, 200 , 65.24, P<0.001). Furthermore, microbial population showed significant difference horizontally (F3, 11 = 3.86, P = 0.04) but not vertically (F1, 11 = 4.60, P = 0.055) in plastic soil. This result implies that plastic pollutants can migrate horizontally to contaminate nearby mangroves. Thus, plastic waste should be managed to prevent pollutants from entering the food chain to contaminate humans.
Seed recruitment is a major driver of mangrove restoration globally. It is hypothesized that soil condition and channel hydrology can accelerate seedling recruitment and regeneration after a major disturbance. Species abundance, diversity indices, microbial and chemical concentrations in sand-filled mangrove forest was studied. Eight plots (area = 3902.16 m2) were established with ten transects in each plot in a random block design to investigate the effect of soil conditions on seedling growth. A total of 1, 886 seedlings were physically counted. Seedling abundance was significantly different between red (Rizophora racemosa), white (Laguncularia racemosa) and black (Avicennia germinans) mangroves and nypa palm (nypa fruticans). The most dominant species was black mangroves and the least dominant species was nypa palm. Muddy soils had the most abundant species while sandy soils had the least abundant species. Furthermore, semi-muddy soils had the highest species diversity (H = 0.948) whereas muddy soils had the least species diversity (H = 0.022). The soil metal concentration has no correlation with seed abundance and occur in the order Iron>Nitrate>Copper>Cadmium. Soil with high species diversity had high soil microbial population; however, seedling abundance was correlated with soil nutrients and not heavy metals. Small seeds are easily recruited while good soil condition plus existing hydrological connection facilitated natural seedling regeneration in the disturbed mangrove forest.