Observation of bioturbation and hyporheic flux in streambeds

In the Elkhorn River, burrows, tubes, and sediment mounds created by invertebrate bioturbation were observed in the exposed streambed and commonly concentrated on the fine-sediment patches, which consist of silt, clay, and organic matter. These invertebrate activities could loosen the thin layer of clogging sediments and result in an increase of pore size in the sediments, leading to greater vertical hydraulic conductivity of the streambed (K _v ). The measurements of the vertical hydraulic gradient across the submerged streambed show that vertical flux in the hyporheic zone can alter directions (upward versus downward) for two locations only a few meters apart. In situ permeameter tests show that streambed K _v in the upper sediment layer is much higher than that in the lower sediment layer, and the calculated K _v in the submerged streambed is consistently greater than that in the clogged sediments around the shorelines of the sand bars. Moreover, a phenomenon of gas bubble release at the water-sediment interface from the subsurface sediments was observed in the groundwater seepage zone where flow velocity is extremely small. The bursting of gas bubbles can potentially break the thin clogging layer of sediments and enhance the vertical hydraulic conductivity of the streambed.     

污水土地处理存在的主要缺点及其解决方法

污水土地处理是一种高效、低耗、简便并具有良好脱氮除磷效果的污水就地处理技术,特别适用于小城镇、农村等缺乏排水管网与污水处理系统的地区。该技术已经在国内外得到了较为广泛的应用,但其大面积推广仍然面临着渗滤系统易堵塞、磷穿透和温室气体排放等诸多问题。堵塞会直接导致系统瘫痪;磷穿透会对地下水及周边地区造成二次污染;温室气体排放则会加剧全球暖化趋势。本文就这些问题的发生、解决方法等的研究情况进行了回顾,最后对该技术应用前景作了展望。