Community metabolism and greenhouse gas emissions in abandoned tropical salt pans

Abstract

A large area of coastal wetlands has been converted into solar salt pans over thousands of years. However, salt production declined significantly from the 20th century onward, leading to the abandonment of many salt pans globally. Coastal wetlands are generally recognized as blue carbon ecosystems, but little is known about the carbon flux of abandoned salt pans. This study aimed to assess the carbon flux of abandoned tropical salt pans, using a case study in Budai, southwestern Taiwan by measuring community metabolism and greenhouse gas (GHG) emissions. The results of community metabolism showed that the pelagic community of the salt pans is autotrophic, which is closely related to water chlorophyll a concentration. However, the benthic community is heterotrophic, which is influenced by water temperature and dissolved inorganic phosphorus concentration. The combined metabolism of pelagic and benthic communities in the salt pans exhibited an average carbon absorption of 111.5 g C m⁻² yr⁻¹. The results of GHG emissions measured with floating chambers indicated that the CO₂ flux into the salt pans averaged 139.3 g CO₂ m⁻² yr⁻¹, but a small amount of averaging 354.8 mg CH₄ m⁻² yr⁻¹ and 136.0 mg N₂O m⁻² yr⁻¹ was emitted from the salt pans. Consequently, the net GHG balance indicated that the salt pans serve as systems for removing GHG at an average rate of 92.6 g CO₂e m⁻² yr⁻¹. The CO₂ removal capacity of abandoned tropical salt pans performed better than that of unvegetated coastal wetlands, showing the potential to mitigate climate change.