ABSTRACT: The 1-step and multiple-step KCl extraction technique was used to evaluate quantitatively the distribution of adsorbed NH₄⁺ in the 0-5 cm strata of 2 intertidal muddy structures from Marennes-Oléron Bay, France. KCl extraction efficiency was higher in the reconstituted sediment slurries and decreased significantly in the presence of porewater ions, leading to underestimations of the size of the pool of adsorbed, easily desorbed NH₄⁺. Various pools of adsorbed NH₄⁺ were displaced from the sediment after reaction with KCl in multiple steps. Pools of tightly bound NH₄⁺ were much larger in runnels as opposed to ridges, and accounted for up to 32% (ridge) and 40% (runnel) of the NH₄⁺ desorbed from the sediment. These pools have important implications for the calculation of the K_D value, the dimensionless NH₄⁺ distribution coefficient. Differing relationships between easily desorbed NH₄⁺ or tightly bound NH₄⁺, on the one hand, and the sediment grain size, CaCO₃ and N content, on the other, suggest multiple origins for particulate matter in the sediment.

KEY WORDS: Ammonium · Adsorption · Mudflat · Ridge · Runnel

Published in MEPS Vol. 182 (1999) on June 11
ISSN: 0171-8630. Copyright © Inter-Research, Oldendorf/Luhe, 1999