Abstract
This study is based on the comparison of nutrient and heavy metal concentrations in soils from waste dump sites in mangrove and non mangrove forest i.e. municipal areas. Nine soil samples were collected randomly at three sites in each location with soil auger, 5 cm below the top soil (n = 18). The soils were placed in polyethylene bags and sent to the laboratory for physicochemical analysis for nutrients: Calcium (Ca), Potassium (K), Magnesium (Mg), Manganese (Mn), Phosphorus (P) and Sulphate (SO4) and heavy metals: Zinc (Zn), Lead (Pb), Copper (Cu), and Cadmium (Cd) concentrations. The metals were measured by UV/visible spectrophotometric method using HACH DR 890 colorimeter (wavelength ~ 420 nm). The result indicates that there was no significant difference in heavy metal concentration between mangrove and non mangrove soils (F1, 88 = 0.24, P > 0.05). However, heavy metals were higher in non-mangrove than in mangrove soil. Zinc had the highest overall concentration (37.9±6.7 mg/l) followed by Pb (12.7±3.1 mg/l) and Cu (10.0±1.4 mg/l) in non-mangrove soil, whereas Cd was ten times higher in mangrove (0.4±0.2 mg/l) than in non-mangrove (0.04±0.03 mg/l) soil. The order of heavy metal concentration in mangrove soil is Zn>Pb>Cu>Cd and in non-mangrove soil is Zn>Cu>Pb>Cd. In contrast, there was a significant difference in nutrient concentration between mangrove and non-mangrove soils (F1, 88 = 4.39, P Mg>K>SO4>Mn>P and in non-mangrove soil is Ca>Mg>K>Mn>SO4>P. There was a slight a positive correlation between the nutrient and heavy metal concentration (R2 = 0.016, n = 90, P = 0.001). Results show that municipal soil is more polluted with industrial waste than mangrove forest soil as a result of high anthropogenic activities. Thus harmful metals from mangrove and non mangrove soils can enter the food chain and drinking water source leading to adverse health effect.
Highlights
Waste is a material that is no longer useful to the production system [1], but useful to another process
Heavy metals were higher in non-mangrove than mangrove soil (Table 2)
Nutrient elements were higher in non-mangrove than mangrove soils in Ca, K, Mg, Mn and P while SO4 was higher in mangrove than in non-mangrove soil (Table 3)
Summary
Waste is a material that is no longer useful to the production system [1], but useful to another process. Mangroves are habitat specialist and do not grow outside the coastal environment. They are halophilic, and can survive in highly saline environment [3]. They reduce the intake of excess salt into their system in three ways: (1) by shutting off the intake of excess salt through their root; (2) exudation of salt crystals from their leaves, and (3) storage and expulsion of salt through senescent leaves [4]. The growth of mangrove in wetland areas predisposes them to anthropogenic action of waste disposal. Since mangroves are found in the interface between the land and the sea they become recipients of waste disposed on land or in water. Mangroves are affected by chemical contamination from upland run off during erosion from heavy down pour [5].
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