Assessing Heavy Metal Load of Fish and Shorebirds in The Densu Delta Ramsar Site, Ghana
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Date
2017-06
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University of Ghana
Abstract
The study aimed at assessing the impact of pollution on shorebirds at Densu Delta in Ghana. In view of this study, data on trace metals in water, sediment and biotic factors (fish and shorebirds) were collected and analyzed from August 2016 to February 2017 in four sampling stations within the Densu Delta. The trace metals assessed from the study were copper, zinc, cadmium, arsenic and mercury. From the study, the dominant trace metals assessed in water, sediment, fish and shorebirds were copper and zinc. From the wet season, the average concentration of copper and zinc in sediments was 6.68 ± 0.24 mg/kg and 28.99 ± 0.95 mg/kg respectively. For the dry season, the average concentration of copper and zinc in sediments was 6.01 ± 0.21 mg/kg and 30.02 ± 0.99 mg/kg respectively. Regarding water samples, the average concentration of copper and zinc was 1.54 ± 0.11 mg/kg and 2.98 ± 0.38 mg/kg respectively during the wet season while in the dry season, the mean concentration of copper and zinc was 1.11 ± 0.07 mg/kg and 13.04 ± 0.4 mg/kg correspondingly. Mean concentrations of these dominant trace metals between the dry and wet seasons were significantly different (p < 0.05). Concerning fish samples, the mean concentration of copper and zinc was 0.14 ± 0.17 mg/kg and 5.35 ± 0.81 mg/kg correspondingly for Sarotherodon melanotheron (Blackchin tilapia) while for Coptodon zillii (formerly known as Tilapia zillii) (Red belly tilapia) the mean concentration of copper and zinc was 0.11 ± 0.09 mg/kg and 4.20 ± 0.56 mg/kg correspondingly. However, the variation in dominant trace metals for both fish species was not significantly different (p > 0.05). Regarding shorebirds, the study focused on three main species including Cerylerudis (Piedkinfisher), Phalacrocorax africanus (Longtail Cormorant) and Egretta ardesiaca (Black Heron). The mean concentration of
copper was 1.57 ± 0.24 mg/kg, 6.16 ± 0.55 mg/kg and 11.89 ± 0.15 mg/kg correspondingly for Cerylerudis (Piedkinfisher), Phalacrocorax africanus (Longtail Cormorant) and Egretta ardesiaca (Black Heron) while for zinc, the respective concentrations were 4.36 ± 0.75 mg/kg, 12.41 ± 0.01 mg/kg and 17.58 ± 0.16 mg/kg. The variation in concentration of the trace metals for the shorebirds was significant (p < 0.05). Correlation analysis in terms of trace metals revealed a strong association (R2 = 0.81 – 0.93) with fish (prey items). From the results, the concentration of the dominant trace metals in the shorebirds was below the threshold limit, indicating that these shorebirds within the Densu Delta of Ghana are not polluted. To ensure that these bird species are protected from pollution, some recommendations have been provided including consistent environmental monitoring of the Densu Delta by appropriate authorities
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Keywords
Densu Delta, concentration, copper, trace metals, Phalacrocorax africanus, shorebirds, Cerylerudis, fish