Carbonate system variation evidences the effect of seasonality in carbon uptake in a tropical seagrass meadow of South Caribbean

Abstract

We explore the variation of the carbonate system in the water column over a seagrass meadow under ecological restoration and its correlation with Net Primary Production (NPP), Net Calcification (NC) and Eutrophication, in a small coralline island within the Seaflower International Biosphere Reserve, Colombian Caribbean. We assessed one point within seagrass and another devoid of seagrass, during dry and rainy seasons. Dry season was characterized by higher levels of pHT (total scale), descending levels of Dissolved Inorganic Carbon (CT) along the day, and net fluxes of carbon towards the ocean. Rainy season presented lower pHT values and carbonate variables not correlated with hour in the meadow, while the area presented fluxes of CO2 towards the atmosphere. NPP in the rainy season decreased by 39% in the point without seagrass and by 95% in the seagrass respect to dry season. NC in the meadow registered values 3.2x higher in dry season than in rainy season. These phenomena evidenced a shift in NPP from seagrass to water column, a strong remineralization process, and loss of sheltering function for calcifying organisms localized in the meadow during rainy season. These findings coincide with previous evaluations in the island, which have shown lower rates of seagrass growth and organic carbon accumulation in sediment during rainy season. Possible explanations include carbon import from adjacent ecosystems and influence of cultural eutrophication. Our results suggest the importance of runoff and eutrophication control to protect carbon sequestration ability and improve the outcome of ecological restoration processes in tropical seagrasses.