Phosphate buffering in mangrove sediment pore water under eutrophication and deforestation influences

Abstract

Phosphorus (P) behavior was evaluated in mangrove wetlands impacted by urban sewage, including a deforested site. Sediment cores were analyzed for grain size, organic carbon, total nitrogen, stable isotopes (δ13C and δ15N), P contents, and pore water PO43− concentrations and net consumption/production rates. Under stronger eutrophication influence, significantly higher P (1390 vs. <1000 μg/g), δ15N (8.9 vs. <6.7 ‰) and algal material contents (with lower C/N ratio and heavier δ13C) occurred. Depth-integrated PO43− consumption rates in eutrophicated sites were up to two orders of magnitude higher (at the deforested site) than in a moderately preserved mangrove. The whole core of the moderately preserved site presented no saturation of PO43− buffering capacity, while more eutrophicated sites developed buffering zones saturated at ∼18–26 cm depth. Contrasting to nearby subtidal environments, eutrophication did not cause larger pore water PO43− concentration, evidencing the role of PO43− buffering on P filtering by mangrove wetlands.