Migratory bird aggregation drives seasonal greenhouse gas hotspots in restored wetlands

Ecological restoration of coastal wetlands has contributed to reversing biodiversity loss, but its effects on greenhouse gas emissions remain poorly understood. Here, we present three years of field measurements from restored wetlands in Southeast China, comparing areas with and without dense migratory waterbird congregations. Results indicate that carbon dioxide and methane emissions were significantly higher in waterbird-influenced plots, but only during autumn and winter when bird populations peaked (P < 0.001). Bird droppings increased nutrient availability in the soil and water, which in turn stimulated microbial activity and enzymatic reactions. Meanwhile, bird-induced oxygen consumption promoted anaerobic conditions, which increased the abundance of methanogens while suppressing methanotrophs. These combined effects drove seasonal surges in greenhouse gas emissions. Collectively, our findings identify migratory bird aggregation as a key driver of seasonal emission hotspots in restored wetlands, and highlight the need for long-term, high-frequency monitoring frameworks that capture these seasonal biological pulses when assessing the climate benefits of wetland restoration projects. Increased guano deposition and oxygen consumption from migratory birds result in seasonally higher greenhouse gas emissions, which may affect carbon budgets in restored wetlands, according to three years of field measurements in the Shanyutan Wetlands of Southeast China.