Conclusion

The nutrient and heavy metal concentration in sediment and macrophyte samples from Varthur Lake was assessed through standard protocol of representative samples. Carbon and nitrogen values in sediment were higher at depths ranging from 0.25 to 1 m and at the northwest and northeast side of the lake. Lower C and N values were observed in the samples collected at the depth greater than 1m, at middle and at lake outlets. Among macrophytes, highest C and N was in the shoots of Colocasia esculenta and Alternanthera philoxeroides respectively. Heavy metals concentrations were higher in the sediment samples of north shoreline and inlets. Alternanthera philoxeroides and Eichhornia crassipes had higher concentrations of heavy metals. Sediment samples had heavy metals in the order Cu > Zn > Cr > Ni > Pb >Cd, while in macrophytes samples Cu > Zn > Cr > Pb > Ni > Cd. Thus, the Varthur lake acted as a sink to nutrients and metals. The study highlights phytoremediation potential of macrophytes and caution to be exercised while using these macrophytes as either vegetable or fodder to prevent heavy metal contamination in the biotic food chain. The present study also demonstrated the potential of macrophytes and sediments in the removal of nutrients and heavy metals. Hence, taking advantage of phyto and phyco remediation prospects, constructed wetlands integrated with algal pond, at the inlet of each water body would help in the treatment and mitigates contamination of water bodies.

Acknowledgement

We are grateful to (i) Gautam and Vasantha Jagadisan Endowment– Lake Rejuvenation Indian Institute of Science, Bangalore 560012; (ii) The Ministry of Environment, Forests & Climate Change, Government of India and (iv) UNSD & MoSP, The Ministry of Statistics and Programme Implementation, Government of India for the financial and infrastructure support. We thank local stakeholders for actively taking part in the scientific discussions and cooperation during field data compilation. We are grateful to Madras Engineering Group, Bangalore, Indian Army for actively supporting the field sampling exercise. We are grateful to the official languages section at IISc for the assistance in language editing.