Stable isotopes of carbon (δ13C), sulfur (δ34S), oxygen (δ18O), hydrogen (δ2H), nitrogen (δ15N), and radioactive isotope of hydrogen (tritium) have been applied in combination with conventional techniques (chemical) to investigate Karachi coastal water pollution due to Layari and Malir rivers, which mainly carry the domestic and industrial wastewater of Karachi Metropolitan. Heavy metal contents of the Manora Channel and southeast coastal waters were higher than the Swedish guidelines for the quality of seawater. By contrast, heavy metal concentrations in coastal sediments were found to be significantly higher than that of seawater. Mn and Ni contents in sediments of entire coast (Manora Channel, southeast and northwest coast) were above USEPA guidelines except at Buleji site, whereas Cr, Zn, and Cu levels only in Manora Channel sediments were higher than USEPA guidelines. The higher heavy metal contents of Manora Channel water and sediments can be attributed to an influx of a major portion of untreated industrial and/or domestic wastewater. Layari and Malir river water was observed to be depleted in δ13C(TDIC)and δ34S, which showed heavy influx of sewage into these rivers. Manora Channel water was also depleted in δ13CTDIC and δ34S during low tide environment, showing a large-scale domestic wastewater mixing with seawater. Southeast coastal water was found to be slightly enriched in δ13C(TDIC) and δ34S and exhibited mixing of relatively small quantity of sewage with the seawater as compared to the Manora Channel. δ13C(TDIC) and δ34S contents of northwest coastal water were close to the values meant for normal seawater. δ13C and δ15N contents of Karachi coastal seaweed ranged from -31.1‰ to -4.9‰ PDB and from 6.1‰ to 17.8‰ air, respectively. The average δ15N values (10.2‰ air) of Ulva spp. collected from nonpolluted northwest coast was higher as compared to the average δ15N contents (8.0‰ air) of Ulva from the Manora Channel, suggesting that nitrogen isotopic ratios of Ulva spp. could be a good indicator of sewage pollution. The results of a two-component isotope mass balance equation using δ13C and δ34S values for Layari and Malir rivers and coastal water indicated that tide conditions and distance of sampling site from the pollution source were the main factors to control the transport and dissemination of Layari river pollution into the Manora Channel. High tide environment slowed down the Layari river water mixing with seawater coupled with a gradual decrease in pollution levels from the Layari River outfall zone to the Manora Lighthouse.
Part of the book: Applied Studies of Coastal and Marine Environments