Fate, transport, and toxicity of soluble salts in industrial wastewater used to irrigate hybrid poplar (Populus spp.) trees

Disposal of saline wastewaters is a major problem worldwide. They are difficult to treat, and their discharge to rivers and streams is heavily regulated. Use of hybrid poplar trees for phytoremediation, treatment of landfill leachate, and wastewater irrigation applications is an emerging technology. It is the subject of this thesis to investigate land application of saline wastewater to hybrid poplar trees, with focus on toxicity, movement of soluble salts in the root zone, and evapotranspiration potential of the trees.; The toxicity of a high chloride, saline wastewater (2000 mg/L Cl{dollar}{bsol}sp{lcub}-{rcub}{dollar}, 6 to 7 dS/m) to eight clones of hybrid poplar was determined in greenhouse studies and at a 2-ha prototype. At the prototype, hybrid poplar response to saline drip and spray irrigation were compared. Suction lysimeters and tensiometers were installed at the prototype to monitor movement of applied salts and soil moisture profiles.; Horizontally heterogeneous zonal salinity experiments showed increased tolerance of hybrid poplar to zones of high salinity if a portion of the root zone was maintained at low salinity. Tests of 8 clones showed that there was a wide range in level of salinity tolerance even for poplar hybrids of the same parental cross. Most tolerant clones included both Populus deltoides x P. nigra and Populus trichocarpa x P. deltoides hybrids. When 1 and 7 dS/m solutions were compared, the decrease in both yield and transpiration was consistent across several sites with trees of varying sizes, averaging 19-24%. The estimated seasonal average K{dollar}{bsol}sb{lcub}{bsol}rm c{rcub}{dollar} value (alfalfa reference crop) was 0.85 for spray and 1.0 for drip irrigation. Spray irrigation with saline water dramatically reduced growth and resulted in leaf toxicity symptoms. Salts at the prototype were generally retained near the soil surface for most of the growing season in the areas between the tile trenches. Greater growing season movement of applied salts was associated with proximity to the tile trenches.; Hybrid poplar trees proved surprisingly tolerant to a high salinity, high chloride wastewater. Hybrid poplars could conceivably be used to treat and evaporate saline wastewater, but the design of the system is critical.