连续流湿地中DO、ORP状况及与植物根系分布的关系

构建了水平潜流芦苇人工湿地以处理富营养化河水.在连续运行的近2a时间中,对湿地芦苇根系分布、湿地水体溶解氧(DO)、氧化还原电位(OBP)的时空变化及水力负荷(HLR)对DO、ORP的影响等进行了研究.结果表明,当年生芦苇95%的根系生物量分布在0～20 cm的基质层中,第2个生长年中97%的根系生物量分布在0～35 cm的基质层中,第2年植物根系在深度方向上有了更大的扩展.湿地中上层水体DO和ORP在沿程方向上是逐渐升高的,底层的变化很小,在水深方向上上层大于中底层.受芦苇根系主要分布在基质上层的影响,距地表20 cm的范围内基本属于中等还原环境,中底层水体为强还原环境,水平潜流湿地内部总体上是厌氧状态的.受植物光合作用及大气复氧作用的影响,湿地水体DO在1d之内先升高后降低.水体DO及ORP随着HLR的增大而降低.考察了植物根区ORP状况及根系分布对水体氧化还原状态的影响,结果表明,根系表面的OBP高达(260.6±54.3)mV,远高于水体的ORP(-220.3±21.5)mV.植物根系的释氧作用提高了根区的氧化能力.根区的好氧微环境不足以改变湿地内部的整体厌氧状态;但湿地上层大量根系分布仍然起到了改善湿地上层环境氧化状态的作用.

DO and ORP conditions and their correlation with plant root distribution in a continuous-flow constructed wetland treating eutrophic water

A subsurface horizontal-flow constructed wetland planted with Phragmites australis was developed and used to treat eutrophic water for nearly two years. The plant root distribution, spatial and temporal changes of dissolved oxygen (DO) and oxidation reduction potential (ORP) in wetland water and their correlation with hydraulic loading rate (HLR) were investigated. The influence of plant root distribution on the redox condition of constructed wetlands (CWs) was further analyzed. In the first year, 95% of the root biomass was distributed in the top 0~20 cm and in the second year, 97% of root biomass was distributed in the top 0~35 cm. In the second year of growth, the plant roots significantly extended through a larger proportion of the wetland substrate. DO and ORP of the upper and middle layers of water increased horizontally with the water flow, but the DO and ORP of the bottom water remained nearly constant. DO and ORP decreased with depth. Because of the influence of root biomass distribution in the upper water layer, the environment from the surface to 15 cm deep was moderately reducing, while deeper layers were strongly reducing. As a whole, subsurface horizontal-flow constructed wetlands with continuous flow are anaerobic environments. Due to plant photosynthesis and atmospheric reaeration, water DO initially increased and then decreased over a day. DO and ORP of wetland water decreased as HLR increased. Measurement of the rhizosphere redox potential showed that the microenvironment of the rhizosphere was more oxidising (ORP (260.6±54.3) mV) than bulk water (ORP(-220.3±21.5) mV). Oxygen transportation of plant to roots enhances oxidation ability of rhizosphere which cannot change the total anaerobic environment but effectively contributes to improve the aerobic condition of upper water layers in the constructed wetland.