IMPACT OF ANTHROPOGENIC ACTIVITIES ON THE WATER QUALITY OF SONGOR LAGOON, ADA, GREATER ACCRA REGION

ABSTRACT

Wetlands are vital ecosystems with important social, economic and environmental functions. The Ada Songor lagoon (located in the Dangbe East district, Greater Accra Region), is an internationally designated wetland (Ramsar site). Intense anthropogenic activities have impacted negatively on the quality of water and sediment in the lagoon. The study assessed the extent of heavy metal, pesticide residues and nutrients contamination of surface water and sediment in the Ada Songor Lagoon. The objective of the study was achieved through the determination of physico-chemical parameters [pH, temperature, electrical conductivity (EC), salinity, total dissolved solids (TDS), alkalinity, turbidity, biological oxygen demand (BOD), total hardness)]; the nutrients load (SO42-, PO43-, NO3-) using UV-Visible Spectrophotometry; major ions (Na+, K+, Ca2+, HCO3-); trace metals (Cd, Cr, Ni, Pb, Co, Zn, Cu, As and Hg) using Atomic Absorption Spectrometry (AAS); and, pesticides residues [organochlorines (OC’s), and synthetic pyrethroids by gas chromatography-electron capture detection (GC-ECD) and organophosphorus (OP’s) by gas chromatography-pulse flame photometric detection (GC-PFPD)]. Na and K contents were determined by Flame Emission Photometry. The water temperature (25.7 to 26.6 oC), fall in the range of 25 to 30 oC suitable for sustainability fish and aquatic organisms. The pH range (8.18 to 9.70) which is typical of coastal waters in Ghana is ideal for aquatic organisms. The TDS range (591 to 1,046 mg/L) is not ideal for water birds spawning since it make it harder for them to find food. BOD ranges from 1.19 to 5.35 mg/L. The pattern of ionic dominance in the lagoon during the present study was K+ > Na+ > Ca2+ > Mg2+. The cationic dominance pattern was similar to that of seawater as observed by other works. Nitrate levels ranges from 0.83 to 0.92 mg/L. PO43- in this study varied from 0.05 to 2.92 mg/L which exceeds the levels in most natural waters. The hydrogen sulphide like smell of the sediment in the lagoon may be due to the levels of the sulphate levels (65.8 to 190 mg/L). The concentration (in ranges, mg/L) of trace metals in water samples were: Cd (