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 is increasingly 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) consistently buffered 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 captures species composition shifts and improves biomass realism over time, revealing the importance of trait-based competition 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.