Isotopic, chemical characteristics and water quality of lagoon and river-water samples in Niigata Prefecture, Japan

Abstract

The monitoring and determination of pollutants in environmental water is very significant from the viewpoint of environmental protection. In this study, the objective was to reveal the quality and characteristics of environmental water samples from Niigata Prefecture in recent years, and to establish a new evaluation method for the behavior of environmental water. For the above-mentioned purpose, the total organic carbon (TOC), chemical oxygen demand (COD), the concentration of major ions and oxygen stable isotopic ratios (i.e., δ 18O) in some river water, lagoon water and groundwater samples in Niigata Prefecture were measured. Moreover, the water temperature, pH, electric conductivity (EC) and dissolved oxygen (DO) were measured in the field. River water, circumjacent groundwater (located near the river), and lagoon water samples were taken monthly at fixed sampling points from 4 rivers (i.e. Shinano River and its two branch streams, Agano River) and 2 lagoons (i.e. Sakata and Toyanogata) in Niigata Prefecture. Consequently, the following matters have been mainly clarified: (1) The relationship between TOC and COD serve as a useful tool for estimating the effect of mixing from other kinds of river-water systems. (2) The concentration of NO 3- in water samples from Sakata was larger than those in other environmental water samples. Particularly, those of spring water in Sakata were 30 to 60 ppm throughout the year. (3) The relationship between the δ 18O values and the TOC was relatively good in the water samples from Sakata. In a lagoon, such as Sakata (not suffering from the inflow of river waters), investigating δ 18O values are of interest as one of the indices of organic pollutants (originated from plankton), as well as for characterizing the origin of local water. (4) The pH values of lagoon water samples were 8 to 9, and those of groundwater samples were 5 to 6. It is considered that lagoon water is supersaturated with oxygen, and groundwater is unsaturated. © 2005 The Japan Society for Analytical Chemistry.