沉水植物苦草对沉积物各形态磷时空分布的影响

监测苦草生长过程中根系及沉积物中磷含量和形态的时空变化,探讨苦草根系在生长过程中对沉积物磷时空分布的影响。聚乙烯塑料桶中铺设沉积物为暴发水华水体的底泥,厚度10cm,干重4 821.00g,底泥铺设完毕后缓慢注入100L水(TP 0.02mg/L)。试验桶种植2g苦草休眠芽。沉积物样品磷形态分析采用国际通用的SMT法,在采集沉积物同时采集苦草样品,测定根系生长情况及根系在沉积物中的分布。结果表明:苦草在生长过程中能降低沉积物各层总磷(TP)、NaOH提取磷(NaOH-P)、HCl提取磷(HCl-P)、无机磷(IP)和有机磷(OP)的含量,沉积物各形态磷含量的下降速率为:NaOH-PHCl-PIP=OP;随着苦草根系的生长,在苦草根系分布区沉积物中各形态磷的含量明显低于非根系分布区。苦草根系通过对环境因子氧化还原电位和pH的改变从而影响根系周围沉积物磷的含量,沉积物中各形态磷含量随着苦草根系面积的增加而减小。

Influence of Vallisneria natans Growth on Spatial-temporal Distribution of Different Forms of Phosphorus in Sediment

Aquatic plants can take up nutrients from the water column through submerged shoots, or from interstitial sediment water through roots. The rooted submerged macrophyte Vallisneria natans absorbs nutrients from both sediment and water. In this study, we monitored plant and root growth, the phosphorus content of roots, sediment and water, and changes in different forms of sediment phosphorus. The experiment was carried out in a controlled laboratory setting and the objective was to explore the effect of the root system on the spatial-temporal distribution of sediment phosphorus. The test group and control (no V. natans) were both run in triplicate. Sediment collected from severely eutrophic water body was placed in polyethylene containers (10 cm thick, 4 821.00 g dry weight), and 100 L water was slowly injected. A dormant bud (~2 g) was planted in each of the test group containers. V. natans and sediment samples were collected at two month intervals to determine root growth and sediment phosphorus content and distribution. Phosphorus forms in the sediment were determined by standard methods. Results show that the roots and biomass of V. natans grew slowly from January to May. By May, the biomass (wet weight) of V. natans was ~21 g in each container, and the average root length was ~5 cm. From May to July, V. natans entered the rapid, warm season growth period and biomass and root length increased rapidly. By July, the biomass reached ~80 g per container and the average root length was 9.8 cm. Nutrient uptake by V. natans decreased sediment total phosphorus (TP), NaOH extractable phosphorus (NaOH-P), HCl extractable phosphorus (HCl-P), inorganic phosphorus (IP) and organic phosphorus (OP); the removal rates of the different phosphorus fractions were ordered as IP>NaOH-P>HCl-P~OP. When the biomass of V. natans was low (0-500 g/m2), the content of TP in the root zone was significantly lower than that in the area without root distribution. At higher biomasses (500-600 g/m2), the vertical phosphorus distribution was more uniform because the roots were more evenly distributed through the sediment. The phosphorus content in water also decreased as V. natans grew, with TP decreasing from an initial concentration of 0.10 mg/L to a final concentration of 0.04 mg/L. In summary, phosphorus content in the root zone was markedly lower than outside the zone and the content of the various forms of phosphorus decreased with increased root distribution. The form of phosphorus in the root zone of V. natans was affected by changes in redox potential and pH.