有機汚濁が進む閉鎖性水域の嫌気的・還元的条件下での水質動態

抄録

  It is essential to study the mechanisms of the decomposition of anaerobic organic matter such as denitrification, iron reduction and sulfate reduction caused by oxygen depletion when considering the conservation and restoration of a closed water area under organic contamination. In this study, we observed the water quality of a reservoir with significant organic contamination due to humic acid, and evaluated quantitatively the water quality changes over time with respect to the oxidation reduction potential (ORP) as well as sulfides, ammonium nitrogen (NH4⁺-N), phosphate-phosphorus (PO₄^3--P), and sulfate ions (SO₄^2-) during an anoxic period. The study showed that the changes of the ORP under anaerobic conditions can be modeled using a logistic regression based on the number of consecutive anoxic days. It was suggested that the higher the initial concentration of nitrate nitrogen was. the smaller declining rate of the ORP was from an oxidized state to a reductive state. Furthermore, it was shown that the increase of NH₄⁺-N,PO₄^3--P, and sulfides over time, as well as the reduction of SO₄^2-, can be evaluated using a linear regression based on the number of days elapsed in which both an ORP level of less than -200 mV and a dissolved oxygen level of 0 mg/l are sustained. The dynamics of inorganic nitrogen, phosphorus, and sulfur compounds can be estimated and predicted using the two above-mentioned regression models without any mathematical model on the complex biochemical processes. This is valid information for the analysis of aquatic environments, which can contribute to the conservation and sustainable management of closed water areas.