Studies on the Release of Ammonium Nitrogen from the Bottom Sediments in Freshwater Regions

II. Ammonium Nitrogen in Dissolved and Adsorbed Form in the Sediments

Abstract

Ammonium nitrogen in bottom sediments may be classified into two types, one dissolved in interstitial water and the other adsorbed on the mud particles. In order to clarify the movement of ammonium nitrogen in the sediments and then to estimate its release rate into the overlying water, the basic behaviour of ammonium nitrogen in the interstitial water of the sediments should be investigated. The present experiments were carried out employing the mud samples collected from Akanoi Bay in Lake Biwa. The concentration of ammonium nitrogen in interstitial water was found to be in equilibrium with the amount of ammonium nitrogen adsorbed on the mud particles and a change in the former was observed to bring about adsorption or desorption of ammonium nitrogen onto or from the mud particles. The equilibrium was attained almost immediately and was affected by the temperature of the mud sample. The adsorption or the desorption in mud particles - interstitial water system should be taken into consideration in order to apply the diffusion process and to clarify the movement of ammonium nitrogen in the bottom sediments.