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

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.

Nutrient regeneration susceptibility under contrasting sedimentary conditions from the Rio de Janeiro coast, Brazil.

Dissolved silicate (DSi), NH4(+), NO3(-) and PO4(3-) susceptibility to be exchanged between sediment pore waters and overlying waters was evaluated in Jurujuba Sound (JS station) and Coroa Grande Sound (CGS station), southeastern Brazil. Sedimentary elemental (C, N and P) and isotopic (δ(13)C and δ(15)N) compositions evidenced stronger anthropogenic fertilization in JS station. Net NO3(-) influxes from overlying waters occurred, which was two orders of magnitude higher under the more fertilized condition. This condition resulted in 6-13-times higher net effluxes of NH4(+), DSi and PO4(3-) to overlying waters. Vertical alternation between production and consumption processes in pore waters contributed for a more limited regeneration in CGS station. This was associated with diagenetic responses to sedimentary grain size variability in deeper layers and biological disturbance in upper layers. Nearly continuous production of NH4(+), DSi and PO4(3-) in pore waters implied in intensified susceptibility to remobilization under the eutrophic condition of JS station.