Resolving the relationship between phosphorus biogeochemistry and phosphorus retention in floodplain forest wetlands.
Dress, William*,1, Cade-Menun, Barbara2, Walbridge, Mark3, 1 Robert Morris University, Moon Twp, PA2 Stanford University, Stanford, CA3 West Virginia University, Morgantown, WV
ABSTRACT- We analyzed soil physical and chemical characteristics, phosphorus (P), aluminum (Al), and iron (Fe) fractions, and P sorption capacities, in 12 southeastern US floodplain forests, to examine variations in P biogeochemistry and underlying soil chemistry as a function of floodplain type, parent material age, and microsite elevation. Surface soils (0-15 cm) were collected from floodplains bordering both alluvial and blackwater rivers, with underlying parent materials of two ages: young Pliocene/Miocene sediments (2-24 million years old) and older Cretaceous sediments (66-144 million years old). We established three 20x50 m sampling plots at each site, and collected soil samples (n=4) from each 10x25 m subplot. Sampling points were characterized as either ridge or swale based primarily on topography. Soils were analyzed for moisture content, bulk density, pH, total carbon (C), nitrogen (N), and phosphorus (P), P sorption capacity, and P, Al, and Fe fractions by sequential extraction. Soil P fractions were also analyzed by 31P nuclear magnetic resonance spectroscopy. Organic P comprised 51.5% of the total P pool overall, and soils from blackwater floodplains and swale microsites had a significantly a greater proportion of organic P. The majority of P was present as orthophosphate (44.1% of total P) and the majority of organic P was present as inositol hexaphosphate (21.6% of total P). Orthophosphate comprised a significantly greater proportion of total P in alluvial floodplains compared to blackwater floodplains (51.0% vs. 39.0%). IHP comprised a significantly greater proportion of total P in young vs. old floodplains (24.5% vs. 20.3%) and blackwater vs. alluvial floodplains (25.1% vs. 18.5%). Overall, there were large differences in P biogeochemistry in relation to floodplain type, parent material age and microsite elevation. Resolving the underlying P biogeochemistry in these wetlands will potentially improve our understanding of mechanisms controlling P retention and transformation. For example, the amount of organic P is significantly correlated with phosphorus sorption index (r2 = 0.39), illustrating that P retention may be greater in blackwater floodplains and swale microsites within floodplains.
Key words: phosphorus retention, biogeochemistry, wetlands
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