Soil Organic Matter Clogs Mineral Pores

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Abstract
Recent N 2 adsorption studies have suggested a ‘pore clogging’ effect on mineral soil phases caused by organic matter coatings. For methodological reasons, this pore clogging effect has been studied only after drying. Our hypothesis was that pore clogging is affected by drying of organic coatings. In our study, we used AlOOH, which has been equilibrated with dissolved organic matter (DOM) and polygalacturonic acid [PGA; (C 6 H 8 O 6 ) n ]. To test our hypothesis, we determined the porosity of moist and freeze‐dried AlOOH samples. Freeze‐dried samples were analyzed by N 2 adsorption, moist samples by 1 H‐nuclear magnetic resonance (NMR). In addition, the samples were characterized by environmental scanning electron microscopy—energy dispersive x‐ray spectroscopy (ESEM‐EDX). Both, DOM and PGA significantly reduced specific surface area (SSA BET ) of AlOOH by 34 m 2 g −1 (15%) and 77 m 2 g −1 (36%). The reduction in SSA BET normalized to the amount of C sorbed was 1.0 m 2 mg −1 DOM‐C and 5.9 m 2 mg −1 PGA‐C. Dissolved OM reduced the pore volume of micro‐ and small mesopores 1 H‐NMR results of moist samples showed that PGA sorption reduced the amount of water in pores 1 H‐NMR. Our results indicate that clogging of micro‐ and small mesopores is not an artifact of freeze‐drying. Polygalacturonic acid seems not only to cover the mouth of AlOOH‐nanometer pores but also to fill them.
Funding Information
  • Deutsche Forschungsgemeinschaft

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