Determining the suitable ecological water level based on the response relationship between landscape connectivity and water level: A case study of Poyang Lake, China

• Grassland and water body constitute the main habitats of Poyang Lake wetland. • There is a significant dynamic tradeoff between grassland and water body. • Grassland shrinks while water body expands when water level rises. • Grassland connectivity decreases while water connectivity increases as water level rises. • The suitable ecological water level was determined based on the response of landscape connectivity to water level. Water level is an important indicator of hydrological regime of lake, and its spatio-temporal variation has a profound impact on habitat quality and biodiversity conservation. How to determine the suitable ecological water level has long been a hot issue in ecohydrology research. Taking Poyang Lake as a case and from the perspective of habitat, this study firstly used the range of variability approach (RVA) to analyze the natural water level regime of the lake. Then, the probability of connectivity (PC) was applied to analyze the dynamics of grassland connectivity and water connectivity after identifying the distribution pattern of grassland and water body at different water levels. Finally, the natural water level regime was corrected to the suitable ecological water level based on the response relationship between grassland connectivity, water connectivity and water level. The results showed as follows: (1) The annual variation of water level in Poyang Lake showed a significant unimodal distribution, with high water level in flood season from April to September and low water level in dry season from October to March of the following year. The annual water level can reach the highest of 22.63 m in July and the lowest of 7.12 m in February from 2000 to 2020. (2) The grassland and water body constitute the main habitats of Poyang Lake wetland. Under the disturbance of hydrological process, they presented the unique dynamic tradeoff relationships of “One shrinks while the other expands” and “One is fragmented while the other is connected”, respectively. With the increase of water level, grassland connectivity decreased dramatically while water connectivity increased progressively. (3) The annual demand for suitable ecological water level is 14.82–15.65 m. In the wet season, the threshold of suitable ecological water is 14.82–16.96 m, while it is 11.75–14.82 m in the dry season. The threshold of monthly suitable ecological water level from January to December is successively as follows: 9.89–14.82, 9.99–14.82, 12.12–14.82, 13.29–14.82, 14.82–15.69, 14.82–14.86, 14.82–16.12, 14.82–15.13, 14.82–16.46, 14.65–14.82, 12.38–14.82 and 10.31–14.82 m. This thesis proposes a new perspective and innovative approach for determining the suitable ecological water level of lakes, which can better guide hydrological regulation, habitat management and biodiversity conservation in lake areas.