||Study on the behavior of pollutants in lagoon waters and the effect of precipitation on the water quality of lagoon
Adilijiang, Tiemuer阿地力江, 木尓
102 , 2015-09-24 , 新潟大学
学位の種類: 博士（工学）. 報告番号: 甲第4082号. 学位記番号: 新大院博（工）甲第433号. 学位授与年月日: 平成27年9月24日
Studies using stable isotopes have been important for valuable research in environmental sciences. Oxygen and hydrogen stable isotope ratios (i.e., δ^<18>O, δD) are widely used to investigate global or local hydrological cycle. Then, regular monitoring and measurement of δ^<18>O and δD in lagoon waters as well as river waters and precipitations have been carried out in this work. Furthermore, in case of lagoon waters, water pollutions due to nutrients or organic materials have been observed in recent years. Therefore, regular monitoring and measurement of nutrients such as nitrogen (N) and phosphorus (P), DOC (dissolved organic carbon) or DO (dissolved oxygen) in lagoon waters as simple index of the pollutants is also significant from the viewpoint of environmental protection. The object lagoons in this research are Sakata Lagoon (the representative lake in Niigata Prefecture, which was registered in Ramsar Convention), Toyanogata Lagoon (the largest lake in Niigata Prefecture) and Zhalong Wetland (the biggest Waterfowl Nature Reserve in China, which was registered in Ramsar Convention). Sakata is famous for the wetland registered “Ramsar Covention”, and has a water area of 43.6 ha. Sakata comprises a large (“Honkata” or “Shitakata” ） and a small (“Uwakata”) freshwater lake with low bogs on the banks. This lake is situated near the major rice cropland in Japan, and was originally formed in an ancient hollow in the seaside dune. The lake has no inflow, and the water is supplied from groundwater of the dune. On the other hand, Toyanogata is the largest lake in Niigata Prefecture (lake area: 162 ha) and is located near the center of Niigata City. The lake is classified as “the first class river” (Water Systems of Shinano River), and flows into Kurinoki River. In addition, to survey the influence of rainfall event on these lagoons and the surrounding rivers, δ^<18>O and δD, the concentration of major ions, nutrients, and heavy metals such as Cr in these water samples after rainfall were also determined as well as those in normal samples. Consequently, the following matters have been mainly clarified: (1) δ^<18>O values of sample waters in Zhalong Wetland are generally large probably because of the effect of evaporation, whereas those of Sakata lagoon are large which may be due to the biological process such as the activity of plankton. (2) Considering the results of nutrients concentrations, the water quality of lagoon (Sakata and Toyanogata) waters in Niigata Prefecture is better than that of Zhalong Wetland in China. (3) δD value of water samples in Sakata was generally larger than that in Toyanogata similarly to the case of δ^<18>O, though remarkable large difference among samples was not found; (4) The pH value of lagoon water samples is almost 6.5-8.5 (which is generally larger than that of river water), and pH at the spot of S1 (downstream point of Lower Lagoon (Shitakata)) is remarkably high (9.0-9.5); (5) Lagoon water has the chemical characteristics contrasting to groundwater with a focus on river water from the viewpoint of pH (acidity or alkalinity) and DO. These matters can be closely related to the biological activity such as photosynthesis due to aquatic plant and phytoplankton and the activity of Crustacea plankton etc. in lagoon. (6) 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. (7) The concentrations of Ca^<2+> and NO^-_3 remarkably increased after rainfall events at Sakata 3. (8) The distribution percentage of “suspended” in most water samples remarkably increased after rainfall event. Moreover, the increase of total Cr content was also found in these samples.