水质水量调控对浅水湖泊草藻转换过程影响分析

浅水湖泊生态系统存在以大型水生植物(草型)为主要初级生产者的清水稳态和以浮游藻类(藻型)为主要初级生产者的浊水稳态.如何保证湖泊维持草型清水稳态,是湖泊富营养化治理的关键.本研究以白洋淀为案例区,将水体中的沉水植物覆盖度与总磷质量浓度作为湖泊稳态类型的评价指标,建立湖泊草藻转换驱动机制模型,探究影响湖泊稳态转化进程的关键驱动因素.结果表明:进水磷质量浓度和换水周期是影响湖泊草藻转换过程的重要参数.进水磷质量浓度长期保持在0.19 g·m-3以上时,湖泊将最终演化为藻型稳态.降低进水磷质量浓度,能有效提高湖泊稳态沉水植被覆盖度,降低稳态总磷质量浓度;湖泊换水周期对稳态沉水植物覆盖度影响较大,减小换水周期,将有利于湖泊向草型演化;同时,从水文管理角度出发,设定以沉水植被覆盖度为指标的不同草型稳态目标,依据换水周期法,计算得到各个稳态目标下,不同进水磷质量浓度下对应的最大换水周期.可通过合理控制湖泊进水磷质量浓度,并依据不同进水磷质量浓度调整换水周期,控制湖泊平均出湖流量等水质水量调控措施,实现湖泊长期保持草型清水稳态,从而为白洋淀水利工程生态调度提供决策依据.

Effect of water quality and quantity regulation on regime shift between phytoplankton and macrophyte in shallow lakes

There are two stable states in shallow lake ecosystem: clear water state dominated by macrophyte, and turbid water state dominated by phytoplankton. Maintaining steady clear water state dominated by macrophyte is a key treatment for lake eutrophication. In Baiyangdian Lake, coverage of submerged plant and concentration of total phosphorus are evaluation index of steady-state type. Driving mechanism model was established to explore steady-state change. Influent phosphorus concentration and water residence time are important parameters affecting conversion between phytoplankton and macrophyte. Influent phosphorus concentration and water residence time could effectively change conversion and determine steady-state results. When influent phosphorus concentration is kept above 0.19 g·m?3 for long, lake will eventually evolve into a steady-state type of phytoplankton. Reducing water residence time in lake was conducive to evolution to macrophyte-type. Maximum water residence times corresponding to different influent phosphorus concentrations were calculated. With proper control of influent phosphorus concentration, adjustment of water residence time according to phosphorus concentration, control of average outflow, lake could retain macrophyte-type clear water state for a long time. This will provide some decision-making basis for ecological operation at Baiyangdian Lake water conservancy project.