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 PO₄^3- 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 PO₄^3- 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 PO₄^3- 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 PO₄^3- concentration, evidencing the role of PO₄^3- buffering on P filtering by mangrove wetlands.

Keywords: Eutrophication; Mangrove deforestation; Mangroves; Net consumption rates; Nutrient sinks; Pore water phosphate.