An investigation into the effect of metals on chlorophyll content and photosynthesis activity of the wetland plant phragmites australis in the lower Diep River, Milnerton, Cape Town

Abstract

A study involving a wetland plant, common reed (Phragmites australis L.) was carried out along the bank of the lower Diep River and the adjacent soil samples from four different sites (Milnerton Lagoon, Lower Estuary, Milnerton Bowling Club and Woodbridge Island), Cape Town, South Africa. The aim was to determine the extent of metal contamination and its impact on physiological indices. Results showed that among the metals evaluated, AI and Fe were consistently higher in all the soil samples (from both river bank and the adjacent soil) followed by Zn, Mn, Pb, Cu, Cd, Co, Cr and Ni. The concentrations of AI in the river banks ranged between 1214.1 - 3176 mg.kg-1 compared with the adjacent soils, where AI concentration ranged from 434.8 - 2445.4 mg.kq". The Fe concentrations from the river bank values ranged from 1136.4 - 4897.2 mg.kg-1 compared with Fe concentrations of the adjacent soil samples which ranged from 402.2 - 2459.8 mg.kg-1 . Generally, Zn ranged from 2.4 - 211.5 mq.kq"; Mn: 5.5 - 48.05 mg.kq': Pb: 0.97 - 71.7 mg.kq"; Cu: 0.3 - 45.9 mg.kq'; Cd: 0.0 - 9.3 mg.kq": Co: 0.2 - 2.7 mg.kq': Cr: 0.3 - 2.1 mg.kg-1 ; and Ni: 0.02 - 2.6 mg.kg-1. Overall, Ni had the lovest concentrations in the ecosystem. Results also showed that the abundance of metals from plant samples were in the order of AI > Pb > Cd > Co > Ni > Cr; and for micronutrients, Fe > Mn > Zn > Cu both in the shoots and roots sampled from all the sites investigated. The values of chlorophylls a, b and total chlorophyll as well as photosynthesis were significantly higher in the P. australis plant samples and from the adjacent soil compared with those from the river bank. These results suggest that contamination of soils and wetland ecosystem by metals over and above plant requirements may affect the chlorophyll and photosynthesis rate of the plant thereby undermining the physiological functioning of plants growing along river systems.