Extreme changes in water level regenerate reed stands and a stable water regime leads to die-off: lessons from the analysis of 40-year satellite times series observations in a shallow lake ecosystem.

Francesco Vuolo , Matthieu Collet, Rasmus Fensholt, Erwin Nemeth, Viktor R. Tóth

Reed wetlands are key to the productivity of shallow lakes, and their condition is tightly governed by water level variability. Using long-term satellite observations, we provide the first analysis linking hydrology and reed vitality at Lake Neusiedl, a major climate sensitive wetland system in the Pannonian Basin. We assembled a 40-year record (1985–2025) of Landsat derived Enhanced Vegetation Index (EVI) and related it to in-situ measurements of surface water levels to quantify the impact of extreme events. The analyses of hydrological droughts in 1990, 2003 and 2022 (a record low) reveal a decline in plant vitality during periods of low water. Temporary drawdowns are expected to enhance vigour through sediment oxidation and litter decomposition, producing vegetation rebounds as the severity of the drought alleviates. A significant increase in productivity was observed following the 2022 event, but not after the 1990 and 2003 events. The analysis shows that reed vitality is not a continuous linear function of water availability or inundation level. Instead, it follows a pulse-response dynamic, where rejuvenation occurs only when critical thresholds of exposure depth and duration are exceeded, enabling oxidation of accumulated litter and sediment organic matter driving long-term die-back. The results provide a quantitative basis for adaptive water level management at Lake Neusiedl and demonstrate how long-term satellite monitoring can guide reed conservation in shallow lake wetlands more broadly.