水位对洞庭湖湿地4种典型沉水植物的影响

近年来,受全球变化及高强度人为干扰的影响,湿地退化严重(洞庭湖湿地枯水期提前、枯水期水位持续降低和浅水洼地减少),导致洞庭湖湿地沉水植物大面积消亡.深入研究洞庭湖低水位对沉水植物的生长影响,对指导沉水植物恢复有重要意义.以我国典型通江湖泊洞庭湖典型沉水植物为研究对象,模拟野外沉水植物主要分布区域浅水洼地水文环境,设置4个水位梯度(25、50、75、100 cm),探讨竹叶眼子菜(Potamogeton malaianus)、黑藻(Hydrilla verticillata)、苦草(Vallisneria natans)和金鱼藻(Ceratophyllum demersum)的生长、生物量和生理活性对水位变化的响应.结果显示:(1)前期底质养分含量为:总氮0.09%、总磷0.09%、总钾3.04%、碱解氮20.87 mg/kg、速效磷10.7 mg/kg、速效钾326.67 mg/kg、硝态氮6.97 mg/kg、氨氮6.59 mg/kg、有机碳1.21%、有机质2.09%,2个月后,不同水位的底质养分含量有差异,100和75 cm水池的养分含量高于50和25 cm,氨氮、有机质和有机碳含量在25 cm水位的水池较高;(2)75 cm水位适合竹叶眼子菜和黑藻生长,100 cm水位适合苦草和金鱼藻生长;(3)100 cm水位有利于竹叶眼子菜的繁殖及生物量积累,75 cm水位有利于黑藻和金鱼藻的繁殖及生物量积累,50 cm水位有利于苦草的繁殖及生物量积累;(4)100 cm水位下的沉水植物酶活性强,75和50 cm水位下的沉水植物次之,25 cm水位下的最弱.以上结果表明,4种沉水植物的生长特征和生物量积累随水位变化,在水域生态恢复中应考虑将水位控制在50~100 cm之间,这样有利于促进种群生物量和水生生态系统的恢复.

Influence of water level on four typical submerged plants in wetlands of Lake Dongting

Due to global changes and high-intensity human activities, serious environmental problems (e.g., the advance of the dry season in Lake Dongting wetlands, the continuous decline of water levels in dry season, and the reduction of shallow water depressions) have led to the large-scale extinction of submerged plants in Lake Dongting wetlands in the recent years. In-depth study of the effect of low water level on the growth of submerged plants in Lake Dongting is of great significance for guiding the restoration of submerged plants. We take the typical submerged plants in Lake Dongting, a typical lake connected to the Changjiang River in China, as a model system, and set up 4 water depth gradients (25, 50, 75 and 100 cm) to simulate the hydrological environment of shallow water depressions in the field where submerged plants are mainly distributed and the responses of the growth, biomass, and enzyme activity of Potamogeton malaianus, Hydrilla verticillata, Vallisneria natans and Ceratophyllum demersum to changes in depth. The results showed that: (1) The nutrient content in the early stage was 0.09% of total nitrogen, 0.09% of total phosphorus, 3.04% of total potassium, 20.87 mg/kg of alkaline nitrogen, 10.7 mg/kg of available phosphorus, 326.67 mg/kg of available potassium, 6.97 mg/kg of nitrate, 6.59 mg/kg of ammonia nitrogen, 1.21% of organic carbon, and 2.09% of organic matter. After 2 months, the nutrient content of different bottom water levels was different. The nutrient content of 100 and 75 cm pools was higher than that of 50 and 25 cm pools. Ammonia nitrogen, organic matter and organic carbon contents of 25 cm pool were highest; (2) The 75 cm water level is suitable for the growth of P. malaianus and H. verticillata, and it is suitable for the growth of V. natans and C. demersum; (3) Under different water level conditions, 100 cm water level is conducive to the reproduction and biomass accumulation of P. malaianus. The 75 cm water level is conducive to the reproduction and biomass accumulation of H. verticillata and C. demersum, and the 50 cm water level is beneficial to the reproduction and biomass accumulation of V. natans; (4) The submerged plants at 100 cm water level have strong enzyme activity, followed by submerged plants at 75 and 50 cm water levels, and submerged plants at 25 cm water level are weakest. The results indicated that water level greatly influenced the growth characteristics and biomass accumulation of four submerged plants. We concluded that restoration of submerged plant populations in the water level of 50-100 cm should be considered in the ecological restoration of waters. It is conducive to the promotion of population biomass and restoration of aquatic ecosystems.