Sulfide Induced Mobilization of Wetland Phosphorus Depends Strongly on Redox and Iron Geochemistry

• Published in: Soil Science Society of America journal Vol. 75; no. 5; pp. 1986 - 1999
• Main Authors: Maynard, Jonathan J, O'Geen, Anthony T, Dahlgren, Randy A
• Format: Journal Article
• Language: English
• Published: Madison, WI Soil Science Society of America 01.09.2011; The Soil Science Society of America, Inc; American Society of Agronomy
• Subjects: Aerobic conditions; Agronomy. Soil science and plant productions; Artificial wetlands; Biogeochemical cycles; Biological and medical sciences; chemical equilibrium; Earth sciences; Earth, ocean, space; Environmental conditions; Environmental protection; Exact sciences and technology; ferric oxide; ferrous oxide; Fundamental and applied biological sciences. Psychology; Geochemistry; Iron; iron oxides; irrigated farming; Nutrient cycles; Nutrient loading; nutrients; Oxides; phosphorus; pollution load; Pore water; sediments; Soil chemistry; Soil science; Soil surfaces; Soils; sorption; Sulfides; Surface water; Surficial geology; Water column; Water quality; wetland soils; wetlands; Non metal; Oxidation reduction; geochemistry; mobilization; Group VIII metal; Transition metal; Earth science; chemical reactions; Group VA element; wetlands; iron; Soil science; phosphorus; sulfides
• ISSN: 0361-5995; 1435-0661
• DOI: 10.2136/sssaj2011.0031

Constructed and restored wetland soils play a key role in the cycling and retention of nutrients from polluted surface waters. Elevated SO42- 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 SO42- concentration and active SO42- reduction in wetland pore waters contributed to elevated pore water PO43- concentration (0.42 -1.29 mg L-1) via SO42- induced P mobilization. Although high concentrations of acid volatile sulfide (AVS) were present in the surface (0-5 cm) layer ( 6.5-10.3 micromol g-1), only ∼8% of the labile Fe pool was S2- bound, leaving sufficient Fe to buffer S2-. 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 PO43- concentrations, can limit the effects of high SO42- loading and SO42- reduction on the mobilization and flux of soil PO43- to the wetland water column.