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Sulfide Induced Mobilization of Wetland Phosphorus Depends Strongly on Redox and Iron Geochemistry
Author(s) -
Maynard Jonathan J.,
O'Geen Anthony T.,
Dahlgren Randy A.
Publication year - 2011
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj2011.0031
Subject(s) - biogeochemical cycle , environmental chemistry , soil water , redox , chemistry , sulfide , sorption , wetland , pore water pressure , phosphorus , cycling , surface water , geology , inorganic chemistry , environmental science , environmental engineering , soil science , ecology , adsorption , geotechnical engineering , organic chemistry , biology , history , archaeology
Constructed and restored wetland soils play a key role in the cycling and retention of nutrients from polluted surface waters. Elevated SO 4 2‐ loading from irrigated agriculture, however, has been shown to affect both the availability and mobility of P in wetland soils. This study investigated the biogeochemical cycling of Fe, S, and P in wetland pore waters and surface soils, to determine the role of sulfides in inducing mobilization of P in a constructed wetland in the Central Valley of California (CVC). Water column, pore‐water, and solid‐phase soil chemistry were measured at three sites, representing a range in wetland environmental conditions (i.e., sediment and nutrient loading, redox environment, and Fe–S–P geochemistry). High SO 4 2‐ concentration and active SO 4 2‐ reduction in wetland pore waters contributed to elevated pore water PO 4 3‐ concentration (0.42 –1.29 mg L −1 ) via SO 4 2‐ induced P mobilization. Although high concentrations of acid volatile sulfide (AVS) were present in the surface (0–5 cm) layer ( x ¯ : 6.5–10.3 μmol g −1 ), only ∼8% of the labile Fe pool was S 2‐ bound, leaving sufficient Fe to buffer S 2− . Additionally, surface soils experienced a three‐ to four‐fold increase in P sorption index (PSI) under anaerobic versus aerobic conditions. Results from solid‐phase chemical extractions and chemical equilibrium modeling showed that this higher PSI may be due to the conversion of crystalline Fe(III) oxides to poorly crystalline forms, the preservation of Fe(III) oxides due to kinetic constraints on microbial Fe reduction, and the formation of Fe(II) oxides. This study demonstrates that mineral dominated wetlands with sufficient Fe to buffer both dissolved sulfide and PO 4 3‐ concentrations, can limit the effects of high SO 4 2‐ loading and SO 4 2‐ reduction on the mobilization and flux of soil PO 4 3‐ to the wetland water column.