Characteristics of the δ15NNO3 distribution and its drivers in the Changjiang River estuary and adjacent waters

• Published in: Chinese journal of oceanology and limnology 2017-03, Vol.35 (2), p.367-382
• Main Author: 王文涛 俞志明 宋秀贤 吴在兴 袁涌铨 周鹏 曹西华
• Format: Article
• Language: English
• Subjects: Algae; Algal blooms; Assimilation; Biological assimilation; Chemistry; Distribution; Earth and Environmental Science; Earth Sciences; Estuaries; Estuarine dynamics; Eutrophication; Fractionation; Nitrates; Nitrification; Nitrogen; Nitrogen isotopes; Nutrient concentrations; Oceanography; Parameters; Phytoplankton; Plankton; Plankton blooms; Rivers; Seasonal distribution; Seasonal variation; Seasonal variations; Shallow water; Subsurface water; Vertical distribution; Water analysis; Water sampling; 同位素组成; 浮游植物; 生物学参数; 硝酸盐氮; 营养盐浓度; 邻近海域; 长江口; 驱动特性
• ISSN: 0254-4059; 2096-5508; 1993-5005; 2523-3521
• DOI: 10.1007/s00343-016-5276-x

In this study, we conducted investigations in the Changjiang （Yangtze） River estuary and adjacent waters （CREAW） in June and November of 2014. We collected water samples from different depths to analyze the nitrogen isotopic compositions of nitrate, nutrient concentrations （including inorganic N, P, and Si）, and other physical and biological parameters, along with the vertical distribution and seasonal variations of these parameters. The compositions of nitrogen isotope in nitrate were measured with the denitrifier method. Results show that the Changjiang River diluted water （CDW） was the main factor affecting the shallow waters （above 10 m） of the CREAW, and CDW tended to influence the northern areas in June and the southern areas in November. 615Nrqo~ values in CDW ranged from 3.21%o-3.55%o. In contrast, the deep waters （below 30 m） were affected by the subsurface water of the Kuroshio Current, which intruded into the waters near 3 I~N in June. The ~iI~NNo3 values of these waters were 6.03%0-7.6%0, slightly higher than the values of the Kuroshio Current. Nitrate assimilation by phytoplankton in the shallow waters of the study area varied seasonally. Because of the favorable temperature and nutrient conditions in June, abundant phytoplankton growth resulted in harmful algae blooms （HABs）. Therefore, nitrate assimilation was strong in June and weak in November. The ~15NNo3 fractionations caused by assimilation of phytoplankton were 4.57%0 and 4.41%o in the shallow waters in June and November, respectively. These results are consistent with previous laboratory cultures and in situ investigations. Nitrification processes were observed in some deep waters of the study area, and they were more apparent in November than in June. The fractionation values of nitrification ranged from 24%0-25%o, which agrees with results for Nitrosospira tenuis reported by previous studies.