水动力条件下苦草对沉积物氮释放的影响

在浅水湖泊中，沉积物易受到水流的扰动释放出原本沉降于其中的氮营养盐。沉水植物一方面能够减少水动力的作用，一方面又能够吸收沉积物中的和已经释放到上覆水中的氮营养盐供其生长同时改善水质。因此，研究沉水植物对沉积物中氮营养盐释放的影响具有很重要的实际意义。借助自主开发的生态水槽，研究苦草（Vallisneria spiraslis L.）在动、静水条件下对沉积物氮的释放的影响。实验装置包括四组水槽，两组动水槽中的一组只铺沉积物，另一组在沉积物上种植苦草，两组静水槽也如此设置。在40 d的实验周期内，我们在实验始末采集沉积物样品，在每一个采样时间点（0、1、3、6、12、20、30、40 d）采集水样，并测定沉积物中总氮含量，原水样中的总氮含量以及过滤水样中的总氮、氨氮、硝氮和亚硝氮的含量。研究结果表明：没有苦草的实验组0～1 cm沉积物层总氮下降幅度较大，有苦草的实验组表面0～1 cm沉积物层氮含量较高。苦草从根系周围沉积物中吸收氮，1～4 cm沉积物层的吸收量多于4～8 cm沉积物层。各水槽上覆水中总氮含量在第1天就有较大的增加，从0.09 mg·L^-1分别升到0.60、0.50、0.379、0.36 mg·L^-1在水动力影响下的增加更显著，后缓慢上升。动水槽中进入到上覆水的氮中80%以上是以溶解态氮形式存在，静水槽中这个比例高达90%以上。苦草对溶解态和颗粒态氮的去除率最高可达27.6%和84.3%。3种氮形态中硝态氮的含量比重较大，在动水条件下，苦草对氨氮，硝氮和亚硝氮的去除率最高可达30.0%、25.0%和60.0%。但苦草对水中氮形态的比例的影响并不明显。以上结果说明水动力条件明显促进沉积物中氮的释放，沉水植物苦草通过保护表层沉积物，吸收下层沉积物中氮，去除进入上覆水中的氮，特别是颗粒态氮和溶解态中的亚硝态

The Impact of Vallisneria spiraslis L. on the Release of Nitrogen from Sediment

In shallow lakes, the nitrogen will release from sediments to the water column when the sediment got disturbed. Submerged plants can not only reduce the hydrodynamic force, but also absorb nitrogen from sediment to improve the water quality in the lake. Therefore, it is very important to study the impact of submerged plants on the hydrodynamic process and the release of nitrogen from the sediment. In this paper, the impacts of Vallisneria spiraslis L. on the release of nitrogen from the sediment under static and dynamical conditions were studied in flumes. The sediments were paved along the bottom of the flumes. Two static conditions and two dynamical conditions with or without planting Vallisneria spiraslis L. in the flume were designed to generate different turbulence on the sediment surface. The sediment samples were taken in the first and last day during the 40 day long experimental period for determining total nitrogen concentration only. The water samples were taken at eight different days, such as 0, 1, 3, 6, 12, 20, 30, 40 d for determining dissolve nitrogen, ammonia, nitrate and nitrite in filtered water. The results showed that the total nitrogen in the surface layer （0～1 cm） of the sediment without Vallisneria spiraslis L. were smaller than that with Vallisneria spiraslis L. The plants absorbed more nitrogen from the middle layer （1～4 cm） of sediment than from the deep layer （4～8 cm）. The total nitrogen in the water column dramatically increased since the first day from 0.09 mg·L^-1 to 0.60, 0.50, 0.379, 0.36 mg·L^-1 respectively, and dynamical condition enlarged this increment. Dissolved nitrogen in the water column took 80%of total nitrogen in hydrodynamic conditions and 90% in static ones. The Vallisneria spiraslis L. reduced both dissolved and particular nitrogen by 27.6%and 84.3%, respectively. The nitrate took a large proportion of total nitrogen in overlying water. The Vallisneria spiraslis L. reduced ammonia, nitrate and nitrite in the water under hydrodynamic condition by 3