Limnological Studies on the Wetland Lake, Al-Asfar, with Special References to Heavy Metal Accumulation by Fish

Problem statement: Al-Asfar Lake is one from the important shallow wetland lakes. It is located on the eastern region of Saudi Arabia, Al-Hassa Province. However, much of their limnology and its biotic information are still unknown to the scientific community. The study aims to follow variations in physico-chemical characteristics, phytoplankton and to determine the sort of pollutants such as heavy metals that are affecting the lake. Heavy metals accumulation by fish is also investigated to assess the public health risks associated with consuming fish harvested from this area. Approach: A regular visit was monitoring the spring over a period of one-year (January 2010-December 2010). Sediment, surface water samples, Phytoplankton and fishes were collected seasonally from different sites within the lake. Results: The data revealed that the maximum content of Cd (0.5 ppm), Cu (2.62 ppm) and Zn (2.6 ppm) were recorded at 5 and 15 cm depth, respectively. Noteworthy is that the highest value of Pb was 7.7 ppm at 1.0 cm depth. The physic-chemical characteristics were subjected to seasonal variations. The data shows that the concentrations of metals in water were found in the following order: Pb²⁺ > Cu⁺² > Zn²⁺ > Cd²⁺ > Mn⁺². The data also shows that there are marked seasonal differences in the quantitative and qualitative composition of the phytoplankton communities in Al-Asfar Lake water. The results confirm the differences of heavy metal accumulation in the different tissues of lake fishes. The highest concentrations were found in kidney, except for Cd and Cu which is found in liver to be highest. The lowest levels were detected in the muscle. Conclusion: The levels of heavy metals recorded in water were generally high, when compared to the international Permissible limits. The analysis of phytoplankton of Al-Asfar Lake indicates that the water of Lake Al-Asfar can be considered as eutrophic. The fishes can be useful as bioindicator of the degree of pollution in aquatic ecosystems. Al-Asfar is indicates heavy polluted in autumn and winter and moderate pollution in spring and summer.