Physiological Responses Of Juncus Effusus (Rush) To Chromium And Relevance For Wastewater Treatment In Constructed Wetlands

Abstract

Constructed wetlands are increasingly applied for industrial wastewater treatment. However, current knowledge of the stress responses of helophytes to selected toxicants such as dichromate is limited. The goal of the experiments presented here was to characterize the physiological response of Juncus effusus to different concentrations of dichromate dependent upon the growth and constitution of the plants.

The growth parameters, shoot length, and dry weight already were strongly affected at low dichromate concentrations of approximately 34 μM. Concentrations of 340 μM impaired chlorophyll fluorescence and a decrease in chlorophyll a started at concentrations higher than 170 μM dichromate. The concentrations of chlorophyll b and carotenoids also were influenced negatively. Thus, the reduction of the pigment content started before any obvious influence on the chlorophyll fluorescence. The highest concentration of dichromate, which caused no permanent inhibition of growth and photosynthesis, was found to be 17 μM K₂Cr₂O₇. In principle, J. effusus is suitable for constructed wetlands to treat chromium-containing wastewater. Because the stress resistance of J. effusus is limited, the maximum concentration of dichromate in the treated wastewater should not exceed 34 μM. The growth parameters, shoot length, and dry weight were sensitive to much lower dichromate concentrations and did react more quickly than the biochemistry-related parameters chlorophyll fluorescence and pigment concentration. Therefore, the example of Juncus effusus shows that the use of only biochemical parameters to define concentration limits for the treatment of dichromate-containing wastewater can lead to incorrect conclusions and result in disturbed long-term operation of the system.

KEY WORDS:

• chlorophyll fluorescence
• constructed wetland
• dichromate stress
• growth parameters
• Juncus effusus

ACKNOWLEDGEMENTS

The authors would like to thank Ms. Ines Volkmann for processing the ICP-AES measurements and Ms. Ursula Winkler for her support in preparing the plant samples. They would also like to thank Mr. Hans-Joachim Stärk for the stimulating discussions and Dr. Rolf Altenburger (all of the Helmholtz Centre for Environmental Research-UFZ, Germany) for supplying a plant growth chamber.