Biomonitoring of selected freshwater macrophytes to assess lake trace element contamination: a case study of Nal Sarovar Bird Sanctuary, Gujarat, India

A biomonitoring study was carried out at Nal Sarovar Bird Sanctuary, a proposed Ramsar site, Gujarat State, India, to ascertain the degree of trace element contamination. The study focused on assessment of trace element contamination in certain aquatic macrophytes to be used as biomonitors, in comparison with the sediments (abiotic monitor) for heavy metal pollution. Good information was provided by analyzing roots, stems and leaves of native aquatic plants (biomonitors) represented by eight species: Bergia odorata, Hydrilla verticillata, Ipomoea aquatica, Najas graminea, Nelumbo nucifera, Phragmites karka, Typha angustata and Vellisnaria spiralis, alongwith surface sediments and water, were analyzed for Cd, Co, Cu, Cu, Ni, Pb and Zn contamination. The highest concentrations of the trace elements were measured in Ipomoea aquatica and the lowest in Bergia odorata. Based on the concentration and toxicity status observed in the lake's vegetation, the six metals are arranged in the following decreasing order: Zn > Cu > Ni > Co > Pb > Cd. Compared with the standard, normal and critical toxicity range in plants, the detected values of Cd and Pb falls within normal range, while that of Co, Ni and Cu were within the critical range. However, Zn showed the highest concentration and alarming toxicity levels, which is considered as one of the most hazardous pollutants in Nal Sarovar Bird Sanctuary. Certain aquatic macrophytes species are also proposed as biomonitors for the investigated heavy metal pollutants. Such result was significant in the plant species such as Ipomoea aquatica and Phragmites karka, which are the two most useful species in biomonitoring studies due to their ability to accumulate elements in high concentration in the roots and their availability throughout the year. The results showed the significant difference in accumulation rate of some metals like Zn, Cu and Ni in different plant organs, which showed more accumulation in root than that of stem and leaves. Also, there is a high positive correlation between combinations of different metal-pairs in either plant's root, stem or leaf system.