Environmental characteristics of lagoon waters in Niigata Prefecture, Japan, and the effect of precipitation on the water quality of lagoon

摘要

To reveal the characteristics of lagoon waters in Niigata Prefecture in recent years, oxygen stable isotope ratios (i.e., δ~(18)O) and the concentrations of chromium (Cr) as well as major ions, and the nutrients such as nitrogen (N) and phosphorus (P) in water samples of Sakata and Toyanogata were determined. Samples were regularly taken at fixed sampling points from these lagoons, and depth distribution was surveyed at one point in Toyanogata. Particularly, to survey the influence of rainfall event on these lagoons, δ~(18)O and Cr specia- tion in some samples were determined before and after rainfall event. Consequently, the following matters have been mainly clarified: (1) In addition to water samples in Toyanogata, δ~(18)O of the sample at Sakata 3 (spring water at shore of south area in Shitakata) increased after rainfall events. (2) The concentrations of Ca~(2+) and NO_3~- remarkably increased after rainfall events at Sakata 3. (3) The distribution percentage of "suspended" in most water samples remarkably increased after rainfall event. Moreover, increase in total Cr content was also found in these samples.