INTRODUCTION

Aquatic plants (Macrophytes) are vascular plants growing in wetlands or on a substrate that is where soils are flooded or saturated long enough for anaerobic conditions to develop in the root zone Cowardin et al.,(1979) and these plants have evolved to adapt to an anaerobic environment (Cronk and Fennessy, 2001). The aquatic macrophytes occur mainly in the shallow region of lakes, ponds, pools, marshes streams and rivers etc. Macrophytes are of considerable ecological and economic importance as they help in the uptake of nutrients and hence help in maintaining the chemical integrity of the respective ecosystem. They contribute significantly to the productivity of water bodies; mobilize mineral elements from the bottom sediments and provide shelter to aquatic macro invertebrates and fishes. Aquatic macrophytes aid in bioremediation and hence wetlands are aptly known as ‘kidneys of the landscape’. They also respond to changes in water quality and have been used as indicators of pollution and are known as ‘bio-indicators’. When there is enough room for colonization and abundant availability of nutrients, macrophytes show a high growth rate. They assimilate nutrients directly into their tissues. Due to these they were used to solve eutrophic problems of freshwater bodies and to remove pollutants (Sudarshan et al., 2017). Macrophytes influence water quality by taking up nutrients, releasing dissolved organic matter and increasing sedimentation by absorbing turbulent energy (Schallenberg and Waite, 2004). A considerable portion of the nutrient is stored by macrophytes and transferred to the next level (consumers) in the food chain and thus regulate the biogeochemical cycle of nutrients. However, species composition and distribution depend on environmental parameters such as light, water temperature, substrate composition, disturbance and quality (Wetzel, 2001; Jafari et al., 2003).

Macrophytes strongly influence water chemistry, acting as both nutrient sinks through uptake, and also aid in moving compounds from the sediment to the water column. They improve water quality through the uptake of nutrients, trace elements and other contaminants (Gersberg et al., 1986; Peverly et al., 1995; Rai et al., 1999). Aquatic macrophytes are excellent indicators of the ecological state of water bodies because they integrate environmental changes over periods of few years and reflect the cumulative effects of successive disturbances (Lawniczak et al., 2010). Due to their relatively high levels of species richness, rapid growth rates and direct response to environmental changes, they are used as phyto-indicators or bioindicators of the status of water bodies (Hellsten, 2001). Macrophytes have no mechanisms regulating uptake of nutrients, hence their impact on environment is through a process of biochemical concentration and excretion and increased nutrient concentration in their tissues is the result of nutrient rich aquatic environment (Stankovic et al., 2000).

An important physiological property of aquatic vegetation, in general, is the ability to accumulate unselectively chemical elements. Taking advantage of this property, many have attempted the water purification through aquatic vegetation to remediate nutrients, heavy metals and other pollutants (DeBusk et al., 2001; Nirmal et al., 2008; Srivastava et al., 2014; Pawan et al., 2015). Studies reveal that the bioaccumulation of metals in a plant species also relies upon the abiotic factors like temperature, pH, and concentration of chemical elements (Matagi et al.,1998). This also helps in characterising the water body through ecological monitoring of water quality.

attempted the water purification through aquatic vegetation to remediate nutrients, heavy metals and other pollutants (DeBusk et al., 2001; Nirmal et al., 2008; Srivastava et al., 2014; Pawan et al., 2015). Studies reveal that the bioaccumulation of metals in a plant species also relies upon the abiotic factors like temperature, pH, and concentration of chemical elements (Matagi et al.,1998). This also helps in characterising the water body through ecological monitoring of water quality.

Metals when discharged into the aquatic environment undergoes physical, chemical and biological changes and binds with the particulate matter and ultimately settles in the sediment (Rai, P.K., 2009). Metal accumulation in plants varies from species to species. Plants uptake metals from soil either passively through mass flow of water into roots or direct transport through the plasma membrane of root epidermal cells (Yoon et al., 2006). Nevertheless, abilities to take up and accumulate various trace elements in the tissues depend on plant species, evident from the several studies focussing on select species (Rai et al., 1999; Lee et al., 1981; Rai et al.,1999; Zayed et al.,1998; Qian et al.,1999; Zhu et al.,1999; Wang et al., 2002; Kamal et al., 2004). Some species are hyper accumulators with higher abilities to accumulate metals in their biomass. The investigations of the role of macrophytes at the land-water interface are vital as the aquatic macrophytes are involved in many ecological and environmental processes (Mara Lucia Rodrigues Costa and Raoul Henry, 2010). Aquatic plants are often used as bio-indicators of water quality, filters of particulate matter, trapping sediments, bioremediation (removal of nutrients and heavy metals) and improvement of water quality. Phyto monitoring of chemical composition would provide insights to the uptake of nutrients during different growth phases (Barbieri and Esteves, 1991; Gerloff and Krombholz, 1966), and also the nutritional value of the plants. The nutrient pool assessment helps in determining the nutrients balance in the environment including uptake by primary producers (Mara Lucia Rodrigues Costa and Raoul Henry, 2010).

The focus of the current study are (i) to assess the phyto-diversity with the biomass and nutrient (carbon, nitrogen and phosphorus) content and (ii) to assess heavy metal (Cadmium, Copper, Chromium, Nickel, Zinc and Lead) uptake capability in phyto samples from Jakkur wetland, Bengaluru.