Role of water level fluctuation on aquatic vegetation in lakes

This paper analyzes the impact of lake water level fluctuation on aquatic ecological systems based upon studies documented in a wide range of literatures throughout the world.Lake water level fluctuation(LWLF) plays a significant role in ecological restoration and ecosystem management.The impact of LWLF on aquatic ecological systems has been widely studied in recent years,with some of the more recent studies focused on the relationship between LWLF and aquatic vegetations,particularly submerged plants.It is important to maintain an ecologically suitable water level to sustain a healthy lake ecosystem.An ecologically suitable water level is in general characterized by the magnitude,frequency,timing and duration of water level fluctuation.As suggested by many studies,LWLF impacts aquatic ecosystems in both direct and indirect ways,and at various scales from the very small to the ecosystem level scales.LWLF demonstrates different patterns,including short-and long-term LWLF,as well as long-term high and low water levels.Winds and waves are the dominant factors causing short-term LWLF with associated increase in total suspended solid(TSS) concentration and light extinction,which would leads to changes in aquatic and near shore vegetations.Seasonal and long-time LWLF is responsible for more significant changes in lake ecosystems.Long-term high and low water levels,and some abnormal changes in water levels can cause low species diversity or declined biomass.It is considered an important management tool for shallow lake restoration to integrate the role of LWLF into the water-level management framework.The maximum bio-suitable water depth and species diversity index are taken as indictors for water level control.The magnitude,frequency,timing and duration of LWLF need to be adjusted for lake restoration.The main study methods,including statistical analysis of long-time historical data,ecological modelling approach and reference lake approach,are proposed in recent studies.The basic water level control measures include:(1) reducing frequency of flow variation;(2) increasing seasonal variation and avoid extreme conditions;(3) reintroducing seasonal flow peaks;(4) increasing seasonal high flows;(5) reducing high flows,especially those badly timed;and(6) reducing intensity of waterlevel change.Several limitations in the past studies on this topic are identified as:(1) absence of studies on the effects of LWLF on overall aquatic ecosystems;(2) lack of comprehensive ecological modeling studies to quantify the impact of LWLF;(3) lack of sufficient attention to the role of water level control in lake management;and(4) lack of studies on the effects of global warming on LWLF and lake ecosystem.Based on the intensive literature review,this paper presents some potential research directions and methods for water level control and lake ecosystem response.