Dawood University of Engineering and Technology (DUE&T) has joined hands with Karachi University, Sindh University and Mehran University of Engineering & Technology (MUE&T) and PCSIR to lunch a project on “Rehabilitation of Manchar Lake”.
The university has constituted a team comprising Environmental Engineers, Aquatic Biologists, Architects, Chemical Engineers, Nano Material Scientists, and Water Experts.
The team has visited Manchar Lake in Mid August for observation and developing the Project.
A preparatory note for Manchar Lake prepared by Vice Chancellor Dr. Faizullah Abbasi and Dr. Ghulam Mujtaba talks about the remediation treatments for Eutrophic Lakes.
Remediation Treatments for Eutrophic Lakes – Reference to Manchar
Eutrophication causes pronounced deterioration of water quality and widespread environmental problems. Lakes, generally, deteriorate due to excessive loading of nutrients, organic matter, and silt, which increased primary producer biomass and reduced water quality. Eutrophication occurs both due to external sources and internal sources. In the case of Manchar, we need to analyze both and if possible, quantify the impact of each in Manchar’s eutrophication.
Lakes are generally classified as under:
Oligotrophic – low nutrients and biologically unproductive
Mesotrophic – intermediate state of nutrient availability and biological productivity
Eutrophic – nutrient-rich and highly productive
Hypereutrophic – extreme condition of the eutrophic state Need to analyze Manchar for its classification.
Some lake management techniques:
Reduction of external loading
In lake remediation – limiting and controlling the sediment or plankton algae, etc.
However, it is believed that for most in lake techniques to be effective, important external loading sources should be evaluated and controlled. Thus, at Manchar, collection of samples of water and sediments from several points is imperative.
In lake Biological, Physical, and Chemical Treatments:
Biomanipulation – the grazing of algae by large zooplankton. Daphnia enhancement by eliminating planktivorous fish through physical removal or increased piscivory.
“Removal of macrophytes – removing macrophyte biomass from lakes removes nutrient decomposition of organic matter, contributes to oxygen deficiency and sediments phosphorus release, which can be alleviated by macrophyte removal.
Hypolimnetic withdrawal – nutrient-enriched hypolimnetic waters can be preferentially removed. Through siphoning, pumping or selective discharge instead of low nutrient surface water.
Dilution and Flushing – Dilution involves the addition of low nutrient water to reduce lake nutrient concentration. Flushing is the removal of algal biomass.
Hypolimnetic aeration and oxygenation – highly effective at increasing dissolved oxygen in the hypolimnion without destratifying.
Artificial circulation – this is used to prevent or eliminate thermal stratification. It can improve dissolved oxygen and reduces iron and manganese, light to limit algal growth.
Dredging and removal of sediments – it can control both algae and macrophytes. Restrict internal loading.
Phosphorus inactivation and capping – internal phosphorus release is a significant source that could delay recovery of the lake and can be controlled by the addition of alum.
Sediment oxidation – this method reduces internal loading in lakes.
Algicide – this is an older method that has lost its use. It involves the addition of copper sulfate and other algicides.
Conclusion:
In conclusion, it is generally agreed that in lake remediation technologies will usually fail to provide long term relief unless external loads of nutrients are reduced or controlled. The primary aim of in lake remediation methods is to decrease factors that slow lake recovery following reductions of external loads. – ER Report
