Size distribution of dissolved (<200 nm) organic carbon and aluminium in alkaline and humic lakes

Abstract

Chemical equilibrium calculations treating humic substances as the simple diprotic phtalic acid, predicted no AI-humus at pH >6.5 in humic lake water. However, dissolved (<200 nm) organic carbon (DOC) and dissolved AI appeared to be linearly (r = 0.597, P <0.001) correlated in samples from five different humic surface waters in The Netherlands with a DOC range of 10-36 mg.1-1 and a (mean) pH range of 6.85-8.47. Yet, organic carbon (Corg) and AI did no exhibit similar size distributions between 5 and 200 nm revealed by ultrafiltration. Averaged 25% of the Corg and >50% of the AI occurred in the fraction <5 nm. Only in this fraction the Corg and AI were linearly correlated (r = 0.515, P <0.001). This result suggests the presence of organic ligands in the DOG pool of humic waters having smaller molecular sizes and higher AI stability constants than the humic substances used to model aquatic AI speciation.

The Chemistry of Phosphate and Nitrogen Compounds in Sediments

“…showed phosphate adsorption onto Al(OH) 3 in experiments in vitro, where high concentrations of Al(OH) 3 were used in limited volumes. De Haan et al (1991) found concentrations of soluble (< 200 nm) Al between 10 and 50 µg −1 in 5 humic rich Dutch lakes with pH values between 6.85 and 8.5 and suggested a linear correlation with org-C diss . These data are more relevant for P-elimination from sewage water than from lakes and cannot be used in a lake situation.…”