Characterization of Colloidal Phosphorus Species in Drainage Waters from a Clay Soil Using Asymmetric Flow Field-Flow Fractionation

Abstract

Phosphorus transport from agricultural land contributes to eutrophication of surface waters. Pipe drain and trench waters from a grassland field on a heavy clay soil in the Netherlands were sampled before and after manure application. Phosphorus speciation was analyzed by physicochemical P fractionation, and the colloidal P fraction in the dissolved fraction (<0.45 μm) was analyzed by asymmetric flow field-flow fractionation (AF4) coupled to high-resolution inductively coupled plasma-mass spectrometry and ultraviolet diode array detector. When no manure was applied for almost 7 mo, total P (TP) concentrations were low (<21 μmol L), and TP was almost evenly distributed among dissolved reactive P (DRP), dissolved unreactive P (DUP), and particulate P (PP). Total P concentrations increased by a factor of 60 and 4 when rainfall followed shortly after application of cattle slurry or its solid fraction, respectively. Under these conditions, DRP contributed 50% or more to TP. The P speciation within the DUP and PP fractions varied among the different sampling times. Phosphorus associated with dissolved organic matter, probably via cation bridging, comprised a small fraction of DUP at all sampling times. Colloidal P coeluted with clay particles when P application was withheld for almost 7 mo and after application of the solid cattle slurry fraction. At these sampling times, PP correlated well with particulate Fe, Al, and Si, indicating that P is associated with colloidal clay particles. After cattle slurry application, part of DUP was probably present as phospholipids. Physicochemical fractionation combined with AF4 analysis is a promising tool to unravel the speciation of colloidal P in environmental water samples.

Molecular Speciation of Phosphorus Present in Readily Dispersible Colloids from Agricultural Soils

“…Release potential of total P (TP) and molybdate-reactive P (MRP) in colloidal and truly dissolved fractions from soils cultivated with rice (RS) and vegetables (vS). 2004; Henderson et al, 2012;Regelink et al, 2013). Direct evidence of P associated with Fe minerals has not been previously reported for colloidal samples.…”

“…This fractionation neglects mobile colloids, particles ranging from 1 nm to 1 mm (Baalousha et al, 2005), by which P could be transported across long distances. Accumulated evidence indicates that colloid-facilitated P transport is an important mechanism for P transfer from agricultural land to aquatic ecosystems (Heathwaite et al, 2005;Ilg et al, 2005;Siemens et al, 2008;Regelink et al, 2013). Colloidal P (P coll ) has been reported to contribute >50% of total P (TP) in soil water samples (Hens and Merckx, 2001).…”

“…For example, P associated with Fe (hydr) oxides (Fe-P) is sensitive to reducing conditions (Beauchemin et al, 2003), P sorbed on Al (hydr)oxides (Al-P) or calcium phosphate precipitates is likely to be more vulnerable to pH changes (Lindsay et al, 1989), and organic P (P o ) is more bioavailable (Li and Brett, 2013). To date, however, the speciation of P coll has been characterized very generally by the colorimetric method or inductively coupled plasma mass spectrometry coupled with different size-fractionated techniques (Hens and Merckx, 2001;Van Moorleghem et al, 2011;Henderson et al, 2012;Regelink et al, 2013). Molecular speciation of P coll should be addressed to understand the long-term fate and subsequent impact of soilderived P coll in aquatic systems.…”

Salinization alters fluxes of bioreactive elements from stream ecosystems across land use

“…Different from N, P is primarily a particle reactive element, and a large fraction of dissolved P (e.g., up to 88 %; Cai and Guo, 2009) is in the form of colloids or humic Fe (Al-) phosphate complexes (Hens and Merckx, 2001;Turner et al, 2004;Regelink et al, 2013). This is because the sorption capacity for SRP per unit mass is about 5000 times larger for colloids than for the immobile soil matrix (McGechan and Lewis, 2002).…”

“…Salt concentrations in freshwaters are rapidly increasing at a regional scale in the USA and worldwide (e.g., Nielsen et al, 2003;Kaushal et al, 2005Kaushal et al, , 2014aRengasamy, 2006;Findlay and Kelly, 2011;Steele and Aitkenhead-Peterson, 2011;Corsi et al, 2015). Most of the increased salinization can typically be attributed to road salt deicers and other industrial uses, wastewater discharges, groundwater irrigation, saltwater inundation caused by sea-level rise, and human-accelerated weathering (e.g., Findlay and Kelly, 2011;Aitkenhead-Peterson et al, 2009;Ardón et al, 2013;Kaushal et al, 2013).…”