Assessment of the efficiencies of Eichhornia crassipes (Mart.) Solms and Najas pseudograminae (W. Koch) W.J. de Wiilde in removing heavy metals and eutrophying nutrients in Laguna de Bay [Philippines] and contaminated waters

Greenhouse and field experiments were conducted to assess the efficiencies of Eichhornia crassipes (water hyacinth) and Najas tenuifolia var. pseudograminea (digman) as phytoremediators of heavy metal-contaminated and eutrophied waters. Live specimens versus dried biomass were compared in terms of their ability to remove some heavy metals (lead and cadmium) and eutrophying nutrients (nitrogen and phosphorus) under greenhouse and field condition. In the greenhouse experiments, results showed that both Eichhornia crassipes and N. tenuifolia var. pseudograminea are potential phytoremediators. Between the two species, E. crassipes appeared more tolerant to varying levels of pollutants. N. tenuifolia var. psuedograminea showed to be more sensitive than E. crassipes, but has a higher potential in removing Pb within a shorter period of time. N. tenuifolia var. pseudograminea had accumulated 77.44 mg/L Pb and 44.36 mg/L Cd while E. crassipes had accumulated 79.50 mg/L Pb and 76.59 mg/L Cd. At higher concentration of heavy metals HMs (i.e. 100 mg/L Pb and 10 mg/L Cd), carotenoids and phytochelatin content of both plants significantly (P less 0.05) increased; while Chl a, Chl b and glutathione content decreased. The negative correlation of HM with phytochelatin and glutathione (-0.2183) as well as photosynthetic pigments (-0.4283) was an indication of physiological stress. In terms of eutrophying nutrients, E. crassipes and N. tenuifolia var. tenuifolia var. pseudograminea was able to remove 89.83 mg/g N and 69.53 mg/g N, respectively. In terms of bisorption of heavy metals using dried biomass, E. crassipes, dried biomass absorbed more Pb (23.47 mg/g DW) than N. pseudograminea (13.9 mg/g DW) under greenhouse condition. However, in field condition both macrophytes adsorbed lower amount of HM (1.07 mg/g and 1.88 mg/g for E. crassipes and N. tenuifolia var. pseudograminea respectively). This indicated that the dried biomass adsorbed more HM then the living part of the aquatic macrophytes. The results from the field experiment revealed that Pb uptake by N. tenuifolia var. pseudograminea was higher than E. crassipes (14.0 mg/g and 0.05 mg/g; respectively) after 28 days as an Aquatic Macrophytes Biofiltration System (AMBS) component. E. crassipes accumulated more N. and P. than N. tenuifolia var. pseudograminea. N. tenuifolia var. pseudograminea was observed to have higher association indices than E. crassipes and it attracted more faunal species, thereby, increasing biodiversity. On the other hand, water quality was improved when the AMBS was introduced in the Niugan River resulting in the proliferation of fish species.