The sensitivity of shallow-groundwater grasslands to changes in climate and groundwater management

Wet grasslands are among the most effective terrestrial ecosystems for long-term carbon storage, yet their stability can be threatened by climate change and altered groundwater regimes. This study applies the MONICA agroecosystem model enhanced through dynamic coupling with the individual-based grassland model GRASSMIND to evaluate carbon, nitrogen, and biomass dynamics in Brandenburg’s wet grasslands (2021–2100) under three groundwater table scenarios and RCP 2.6, 4.5, and 8.5 climate pathways. Shallow groundwater conditions (∼30 cm) were associated with smaller soil organic carbon (SOC) loss (< 0.6 Mg C ha⁻¹ yr⁻¹), suppressed nitrous oxide emissions, and limited nitrate leaching. In contrast, deep or unmanaged water tables increased aerobic decomposition and mineral nitrogen losses, especially under RCP 8.5, suggesting a critical climate–hydrology threshold around mid-century. Coupling MONICA with GRASSMIND allows species composition shifts to be represented and provides an exploratory assessment of how trait-based competition may influence biomass projections in wet grassland modelling. This study highlights that groundwater level management exerts a stronger control over ecosystem stability than climate forcing alone. These findings underscore the need for adaptive water regime strategies and model-based planning tools to safeguard the climate regulation potential of wet grasslands.