Evaluation of two hybrid poplar clones as constructed wetland plant species for treating saline water high in boron and selenium, or waters only high in boron

Authors: ZHU, HUI - Chinese Academy Of Sciences; Banuelos, Gary

Submitted to: Journal of Hazardous Materials
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/19/2017
Publication Date: 3/21/2017
Citation: Zhu, H., Banuelos, G.S. 2017. Evaluation of two hybrid poplar clones as constructed wetland plant species for treating saline water high in boron and selenium, or waters only high in boron. Journal of Hazardous Materials. 333(2017):319-328. doi:10.1016/j.jhazmat.2017.03.041.

Interpretive Summary: Salts and excessive trace elements in drainage water produced in central California can bioaccumulate and negatively impact a variety of aquatic organisms. Moreover, this consequence can further change the communities of plants, microbes, and aquatic animals in an ecosystem by decreasing species diversity or replacing halo-sensitive species with halophilic species. Therefore, it is necessary to explore effective and affordable strategies for controlling the quality of agricultural effluent in the westside of central California, and thereby protecting the local ecosystem. Constructed wetlands (CWs) may provide an alternative strategy for treating wastewaters with high saline effluents. In regards to using CWs for the treatment of wastewater containing high salts, boron (B) and selenium (Se), however, successful attempts are rare, due to both salt and B toxicities experienced by the plants. Additionally, the interaction between salts and B sometimes cause complicated ecophysiological responses of plants and affect their ability to absorb elements. In the past, the USDA-ARS have identified promising clones from poplar trees that are salt- and boron-tolerant. Poplar trees are ideal because they grow fast, produce high biomass, and have a deep root system. The goal of the present work was to evaluate two salt- and B-tolerant hybrid poplar clones for their suitability as constructed wetland plant species in the phytoremediation of B and Se from saline waters, and B in nonsaline waters. Under greenhouse conditions, mesocosms and hydroponic growing systems were used for testing two salt- and B-tolerant poplar clones for their ability to remove B and Se under saline conditions and B under non-saline conditions, respectively. Both tested poplar clones showed acceptable salt and B tolerance, although each clone showed some differences from the other. They both accumulated a considerable amount of B and Se in their tissues, and were effective in removing B and Se from mesocosms and B from hydroponic systems. In this study, we have demonstrated that both tested poplar clones are potential wetland plants for treating either B- or Se- contaminated saline water or B-contaminated waters. The results obtained from these experiments conducted in mesocosms and hydroponic growing conditions will provide a realistic reference for subsequent testing in pilot wetlands under high salt and B field conditions in central California.

Technical Abstract: Wetland mesocosms were constructed to assess two salt- and B-tolerant hybrid poplar clones (Populus trichocarpa ×P. deltoides×P. nigra '345-1' and '347-14') for treating saline water high in boron (B) and selenium (Se). In addition, a hydroponic experiment was performed to test the B tolerance and B accumulation in both clones. In the mesocosm experiment, clone 345-1 exhibited no toxic symptoms at an EC of 10 mS cm-1, while clone 347-14 showed slight toxic symptoms at 7.5 mS cm-1. The removal percentages of B, Se, sodium (Na), and chloride (Cl) ranged from 26.7-45.6%, 50-69.4%, 18.4-24.0%, and 15.8-23.2%, respectively, by clone 345-1, and from 22.9-29.4%, 31.7-43.8%, 16.5-24.2%, and 14.9-23.9%, respectively, by clone 347-1. In the hydroponic experiment, B toxic symptoms were observed at treatments of 150 and 200 mg B L-1 for clones 345-1 and 347-14, respectively. The greatest leaf B concentrations of 3699 and 1913 mg kg-1 were found in clone 345-1 and clone 347-14, respectively. The translocation factor (TF) of clone 347-14 was less than clone 345-1. Clone 345-1 only showed significantly greater (P<0.05) B removal percentages than clone 347-14 when B treatment was < 20 mg B L-1. In conclusion, both tested poplar clones competitively accumulated and removed B and Se in constructed wetlands. These results will be useful for establishing field-scale wetland projects for removing Se and B from saline effluent produced in the westside of central California.