Ecological status and type of alteration determine the C-balance and climate change mitigation capacity of Mediterranean inland brackish and saline shallow lakes

Understanding the metabolic processes governing carbon biogeochemistry in inland brackish and saline shallow lakes is crucial for assessing their capacity to mitigate climate change. This study aimed to investigate the relationship between carbon biotic processes, metabolic carbon balances, and environmental factors such as salinity, hydroperiod, and ecological status, which can be affected by human activities. We analysed carbon metabolic rates and budgets in 19 sites in the Spanish Mediterranean region, representing diverse ecological conditions. Results revealed that alterations in natural salinity levels, often linked to changes in hydrological regimes and ecological degradation, decreased carbon retention capacity and increased greenhouse gas emissions. Well-preserved or restored lakes exhibited higher carbon retention and mitigation capacities, particularly those with lower salinity levels, indicating higher biological activity. However, higher salinity levels mitigated methane emissions, reducing warming potential risks. The study emphasised the importance of proper wetlands management or restoration to enhance their climate regulation services.