两种沉水植物对间隙水磷浓度的影响

为研究两种根系特征的沉水植物在生长过程中对间隙水中磷浓度的影响,选取根系较多的沉水植物苦草和根系相对较少的沉水植物黑藻作为实验材料,监测底泥中间隙水各形态磷含量及环境因子的变化,探讨不同根系特征沉水植物对间隙水中磷的影响。结果表明:黑藻和苦草实验组沉积物间隙水中各形态磷的浓度均呈不同程度的降低,黑藻和苦草对于稳定水质,减少底泥中磷向水中转移具有明显的效果;沉水植物不同,底泥间隙水中溶解性总磷(DTP)和溶解性活性磷(SRP)存在明显差异。实验结束时黑藻组和苦草组间隙水中DTP的浓度分别为0.24,0.01 mg/L,SRP的浓度分别为0.22 mg/L,0.004 mg/L。间隙水中磷的形态主要以DTP和SRP为主,溶解性有机磷(DOP)的含量相对较低。沉水植物对间隙水中磷的吸收是降低间隙水中磷含量的重要原因,苦草的吸收能力大于黑藻。沉水植物根系通过降低底泥p H值,提高氧化还原电位(Eh)的方式抑制了底泥中磷的释放。

Influence of two submerged macrophytes on pore water phosphorus concentration

Submerged macrophytes play an important role in nutrient cycling, especially in shallow lakes. Submerged macrophytes can acquire significant amounts of nutrients from the water via shoots and from the sediment via roots. In most natural situations, root uptake is the primary pathway for nutrients, because the absorbable nutrient concentrations are much higher in the sediment than in the water column. However, submerged macrophyte species vary in their root traits. Some submerged macrophytes, such as Vallisneria natans, have large root systems, while other species, such as Hydrilla verticillata, grow only a few roots per plant. Phosphorus (P) is the most critical nutrient limiting lake productivity, and while submerged macrophytes play an important role in P cycling, little is known about the effects of different submerged macrophyte species on the behavior of P. Therefore, studies of the effects of different root characters of submerged macrophytes on P concentrations are important for understanding lake ecosystems. The purpose of this work was to identify how two different typical submerged macrophytes, H. verticillata and V. natans, affect the behavior of sediment P. We examined P concentrations and environmental factors in aquatic systems growing each of these plant species from May to September, 2012. During that time, we collected samples of sediment pore water, sediment, and column water on days 0, 30, 60, 90, and 120 of the experiment to determine P concentrations. The environmental factors of pH and redox potential (Eh) of the sediment were also measured. The results indicated that P concentrations in pore water of the H. verticillata and V. natans treatments were lower than that of the control group. Both H. verticillata and V. natans had obvious effects on water stabilization and reducing P release from sediment. Pore water concentrations of dissolved total P (DTP) and soluble reactive P (SRP) in the H. verticillata and V. natans groups were significantly different, with 0.24 mg/L DTP and 0.22 mg/L SRP in the H. verticillata treatment and 0.01 mg/L DTP and 0.004 mg/L SRP in the V. natans treatment. P concentration increased after the 90^th day of the experiment in the H. verticillata group, but it remained at a low level in the V. natans group. The pH was lower in the H. verticillata treatment than in the V. natans treatment, while Eh was higher in the H. verticillata group than in the V. natans group, which might explain why P levels fluctuated differently in the two treatment groups. The main P fractions in pore water were DTP and SRP, while the amount of dissolved organic P (DOP) was relatively low. The submerged macrophytes reduced the P concentration in water, sediment, and pore water during their growth periods. Their absorption of pore water P was one of the main reasons for the decreased P levels. Vallisneria natans could absorb more P than H. verticillata. Both H. verticillata and V. natans could reduce the DOP concentration, but there was no significant difference between the two submerged macrophyte species. There was no significant difference between treatments and control groups in DOP, indicating that H. verticillata and V. natans mainly absorbed DTP and SRP. Submerged macrophyte inhibited the release of P from the sediment into the water column by decreasing the pH and increasing the Eh of the sediment. Overall, the submerged macrophytes H. verticillata and V. natans significantly stabilized water quality and reduced the release of P from the sediment to the water.