Phosphorus forms and response to changes in pH in acid-sensitive soils on the Precambrian Shield

Abstract

Baker, S. R., Watmough, S. A. and Eimers, M. C. 2015. Phosphorus forms and response to changes in pH in acid-sensitive soils on the Precambrian Shield. Can. J. Soil Sci. 95: 95Á108. Soil acidification may explain declines in total phosphorus (TP) levels that have been observed in surface waters in central Ontario, Canada, but much of the research on phosphorus (P) mobility in pH manipulated soils has been performed at high P concentrations (i.e., !500 mM). This study investigated P fractionation in acidic (pH 54.6) soils in south-central Ontario and relationships between soil pH and P sorption at relatively low P concentrations to test whether long-term declines in soil pH could have increased soil P sorption. Soils from three forested catchments that vary naturally in soil pH and outlet stream [TP] (0.1Á0.4 mM in 2008) had very similar soil P concentrations and distributions (Hedley fractionation). Only hydrochloric-acid extractable P (i.e., apatite) differed amongst catchments and was greatest at the catchment with the highest stream [TP]. The fraction of P present as labile/ soluble P did not decline with pH as expected and experiments indicated that P sorption at P concentrations between 4.52 and 452.1 mM was insensitive to manipulated solution pH. Soils were, however, able to sorb!90% of P added in sorption experiments at [P] 5452.1 mM. These results suggest that acidification-induced P sorption in upland soils has not contributed to observed decreases in surface water TP concentrations.Key words: Phosphorus, acidification (soil), Hedley fractionation, sorption, Podzols, Ontario (central) Baker, S. R., Watmough, S. A. et Eimers, M. C. 2015. Types de phosphore et re´action de cet e´le´ment aux variations du pH dans les sols du bouclier pre´cambrien sensibles a`l'acidification. Can. J. Soil Sci. 95: 95Á108. L'acidification du sol pourrait expliquer la concentration de phosphore total (PT) plus faible observe´e dans les eaux superficielles du centre de l'Ontario, mais une bonne partie des recherches sur la mobilite´du phosphore (P) dans les sols dont le pH avait e´te´modifie´ont e´teé ffectue´es a`une concentration de P e´leve´e (a`savoir, supe´rieure a`500 mM). La pre´sente e´tude portait sur le fractionnement du P dans les sols acides (pH 54,6) du centre-sud de l'Ontario et sur les liens existant entre le pH du sol et la sorption du P aux concentrations de P relativement faibles. Elle devait e´tablir si l'acidification a`long terme du sol pouvait avoir accru la sorption du P dans le sol. Trois bassins hydrographiques forestiers dont le pH et la de´charge variaient naturellement [PT] (0,1Á0,4 mM en 2008) pre´sentaient une concentration et une distribution tre`s semblables du P dans leur sol (me´thode de fractionnement de Hedley). Seule la concentration de P extractible a`l'acide chlorhydrique (a`savoir, l'apatite) diffe´rait d'un bassin a`l'autre et atteignait un maximum dans le bassin a`la de´charge la plus importante [PT]. La fraction du P correspondant au P labile/soluble ne diminue pas avec le pH comme ...

Phosphorus adsorption characteristics in forested and managed podzolic soils

“…The newly converted managed CAFD had uniform q max , with a depth similar to the mineral horizons of the forested CAFD soils. Acid soils were reported to have a high q max due to conditions that create high P affinities, such as the presence of Al and Fe hydroxy(oxides) on clay surfaces creating larger surface areas and strong bonding energies favoring Al and Fe phosphate precipitation (Baker et al., 2015; Eriksson et al., 2016; Olsen & Watanabe, 1957). The distinct q max of the LFH at the SJRDC forested locations was surprising; the literature also has contradictory opinions on the role of SOM (47.2% for forested SJRDC; Table 2) (Väänänen et al., 2007; Yang et al., 2019), especially in the presence of Al and Fe.…”

Can recovery from disturbance explain observed declines in total phosphorus in Precambrian Shield catchments?

“…Atmospheric inputs to the lakes were not altered, as these organic inputs are considered part of the lake P-load. Initial soil P concentrations were based on values measured by Baker (2014), and soil equilibrium coefficients based on laboratory derived equilibrium P concentrations (EPC 0 ) and Freundlich isotherm values for different soil and land use types (Peltovuori 2006;Väänänen 2008; Koski-Vähälä 2001).…”

“…Soils within south-central Ontario have also been subject to acidification, due to atmospheric deposition of H 2 SO 4 and HNO 3 . In soils with a relatively low pH, such as those overlying the Precambrian Shield, it has been suggested that sulphate (SO 4 2-) has a significant influence on P sorption, where competition between SO 4 2and P leads to lower P retention (Geelhoed et al 1997;Baker et al 2015). It is unlikely that SO 4 2has been the sole cause of P alterations at all sites, given a weak correlation between SO 4 2and P (Eimers et al 2009), and the large differences in rates of P declines between catchments.…”

“…It is unlikely that SO 4 2has been the sole cause of P alterations at all sites, given a weak correlation between SO 4 2and P (Eimers et al 2009), and the large differences in rates of P declines between catchments. It may, however, be a contributing factor in catchments which have been extensively acidified (Baker 2014).…”

Co‐occurrence of browning and oligotrophication in a boreal stream network

“…And although it is well documented that northern Sweden never reached a state of chronic acidification (Bishop et al 2000), the KCS sub‐catchments remain naturally acidic throughout the year (pH range from 4.4 to 6.6) and pH does not show any statistically significant recovery trend ( p > 0.05) for the period. However, there is still a discrepancy among studies on the relationship between pH, P sorption, and declines in surface water P concentration as both positive (Baker et al 2015) and negative (McDowell et al 2002) relationships have been reported in acidic solutions. In the end, a combination of lower rates of biological mineralization, increased activation of Al and Fe sinks, and reduced competition with sulfate for adsorption (McDowell et al 2002; Giesler et al 2005) could all have an impact on P retention in soils, with consequences for DIP supply to streams.…”