A reliability-resilience-vulnerability framework for measuring the influence of changes in water level fluctuations on lake conditions

Abstract

Water level fluctuations (WLFs) are one of the main drivers affecting the structure and function of lake ecosystems. Recent alterations of WLFs in China’s largest freshwater lake (i.e. the Poyang Lake), have received considerable attentions due to its large influences on ecosystem functioning and health. Here, we proposed a reliability (Rel)-resilience (Res)-vulnerability (Vul) framework to quantify the influence of changes in seasonal WLFs on lake conditions. Key parameters of WLFs were identified, including high and low water level thresholds, onset and ending time of high and low water level periods, and daily water level change rate. Reliability, resilience and vulnerability of the Poyang Lake in four periods of water levels (i.e. high and low, rising and retreating) were calculated for each year between 1953 and 2014 based on the occurrence probability, duration and severity of failure events (extreme water level and anomalous water level change rate). We found that mean daily water level between 1953 and 2002 was always lower than that observed between 2003 and 2014 (the time period after impoundment of the Three Gorges Reservoir). High water level period in 2003–2014 was 17 days shorter than that in 1953–2002, while low water level period in 2003–2014 was 53 days longer than that in 1953–2002. Reliability and resilience of the Poyang Lake in 2003–2014 generally decreased compared with those in 1953–2002, especially in the rising and retreating periods, while the vulnerability increased in the two periods. There was a declining tendency in WLFs-based health index particularly after the impoundment of the Three Gorges Reservoir, suggesting that the condition of the Poyang Lake has become worse. This Rel-Res-Vul framework establishes quantitative linkages between WLFs changes and ecosystem conditions, and provides a feasible tool for water level management that is applicable to other lakes with similar hydrological regimes.