Study On The Purification Ability Of Reed Wetlands To Nitrogen And Phosphorus In Sewage

The purification ability of reed wetland to nitrogen and phosphorus in sewage, and the distribution and dynamics of reed rhizomes and roots were studied in Baiyangdian Lake, Hebei.China. In addition, mechanisms on sewage treatment with wetlands were discussed. The main results were shown as fellow:(1) The purification effect of reed wetland on nitrogen and phosphorus in sewage were very obvious. The removal rate of reed wetland on ammonium can up to 94%, on TN can up to 74%, and on TP can up to 97% within one month. The greater the density of reed and the content of nitrogen and phosphorus of sewage to irritate reed is, the stronger the reed wetlands purification ability is .The purification ability of reed different components on nitrogen and phosphorus in sewage is different. Based on per unit weight of the above-ground parts and the below-ground parts of reed, for N, the purification ability of the above-ground parts greater than below-ground parts, but, for P, the purification ability of the below-ground parts greater than above-ground parts. Based on per unit weight of reed , the amount of absorbed N by the above-ground parts was about 2.34times as that by below-ground part. On the contrary, the amount of absorbed P by the below-ground parts was about 1.74 times as that by the above-ground part.(2) From soil surface to the 80cm depth where the reed rhizomes distribute, the length of reed internode increase while the adventitious roots decrease. In addition, the 20~40cm soil section has the highest biomass of rhizome on the whole soil section. According to the classified rhimoze diameter, it could be found that the roots (φ≤1cm) mainly distribute on the 0~20cm soil section, the roots (2cm ≥ φ > 1cm) mainly distribute on 20~40cm, and the roots (φ > 2cm) mainly distribute on 20~60cm. In degenerative reed population, the biomass decrease, and the internode length become shorter and the adventitious roots inclined. In addition, the ration of root (φ ≤ 1cm) increase while the ration of root (φ > 2cm) decrease;(3) From soil surface to the 100cm depth where the reed roots distribute, both the dried weight and length of reed root decrease. According to the classified root diameter, it could be found that the root (φ ≤ 1mm), which is the largest part of the reed roots, mainly distribute on the 0~40cm soil section, the roots (2mm ≥ φ > 1mm) distribute on the 0~80cm soil, and the root (φ >2mm) mainly distribute on 40~6()cm soil. In degenerative reed population, the biomass decrease (42.05%), and the total length of root decline (34. 98%). The root distribution of degenerative reed is shallower than of the normal reed. The biomass of the roots( (φ ≤ 1mm) decrease while the roots (φ > 1mm) increase;(4) In a year, the dynamics of both the reed roots biomass and above ground biomass show one peak, the reed root biomass, however, reaches its peak in August, while the above ground biomass reaches its peak tn October; Great effect of reed on soil has occurred, such as the decrease of bulk density and the increase of the content of soil pore degree, the organic matter, the nitrogen and phosphorous.