A Methods Comparison for Measurement of Dissolved Organic Nitrogen in Seawater and the Variation of Dissolved Organic Nitrogen in the Frequent Harmful Algal Blooms Areas of the East China Sea
|School||Ocean University of China|
|Keywords||Dissolved organic nitrogen Total dissolved nitrogen N ratio East China Sea|
Nitrogen is the growth of marine organisms important nutrients, dissolved organic nitrogen in the ocean marine nitrogen cycle is an important part, but also have an important impact on the global nitrogen cycle. Currently tide ecological phenomena as an exception more and more people's attention, while dissolved organic nitrogen as nutrients can be directly absorbed by phytoplankton, is one of the causes of red tide outbreak. Understanding the ocean dissolved organic nitrogen (DON), total dissolved nitrogen (TDN) and nitrogen ratio (C / N) distribution and influencing factors on the marine nitrogen cycle and red tide research has important implications. Seawater dissolved organic nitrogen (DON) content of total dissolved nitrogen through (TDN) content of less dissolved inorganic nitrogen (DIN) levels obtained. In this thesis, the first measurement of total dissolved nitrogen in seawater (TDN) of two common methods, high temperature combustion method and potassium persulfate oxidation method were compared to determine the sample was measured by the method used. Then take advantage of April 2010, in May and October surveys three cruises on the East China Sea HAB areas of total dissolved nitrogen (TDN), dissolved organic nitrogen (DON) and the ratio of carbon and nitrogen content and distribution characteristics were studied and analyzes them with different environmental factors, mainly the following results: HTC France and PO measured by the standard curve and blank are very close to the theoretical value, the blank values ??are lower precision of both methods are also higher. Spiking experiments recoveries are close to 100%, both methods are relatively stable, good accuracy. In recovery experiments on different compounds and sea as background to the recovery of spiked EDTA experiments, more complete oxidation of both methods, spiking experiments also showed a linear fit both methods are suitable for measurements in seawater TDN . In the field experiment of measuring the sample water, the horizontal distribution of the two sections with the two methods are very close to the results obtained, the oxidation rate, and there are no significant differences in the blank. Vertical distribution fitting results are very similar, but with higher levels of DON PO France when the oxidation rate is slightly lower. And HTC method can simultaneously measured values ??of DOC and DON, making seawater DOC / DON ratios were measured according to a method of consistency, the measurement method is also more convenient, so HTC method than the method is more suitable for this thesis PO seawater TDN sample measurements. HAB areas of the East China Sea TDN and DON content in the investigation have shown time low nearshore lofty shore trends, similar to the distribution of salinity in the estuary with high value, especially near the mouth of the Yangtze River, visible TDN and DON mainly by terrestrial input effects. Also in the red tide outbreak, high values ??of chlorophyll have low value of DON, indicating some DON absorbed by plankton. C / N ratio in the investigation time appeared far shore coastal low-high trend. Shore terrestrial input due to small molecules of organic nitrogen, C / N is relatively low, in the area of ??higher chlorophyll content, C / N ratio close to Redfield ratio, due to the far-shore area of ??organic macromolecules, C / N ratio increased. This paper selected GC, RB and ZB three sections vertically distribution analysis. In these three cross section, TDN and DON are showing the trend of low coastal lofty shore. Shore areas the vertical direction from the surface to the bottom base is successively decreasing trend, far shore opposite distribution of the region. The distribution of three month averages are presented in order of decreasing from the surface to the underlying trend, the surface influenced by terrestrial input. C / N ratio of the trend of the three sections are far shore nearshore high low, middle Redfield ratio closer. ZA3 day and night for the continuous observation of the results showed that, TDN and DON biggest changes are in the 10m level, and in the chlorophyll maximum and minimum respectively, at high and low values, TDN and DON content of diurnal variation was kind enough to light and tides. C / N ratio of the diurnal variation in the water layer is relatively uniform, subject to tidal influence. From the TDN, DON, and C / N ratio and salinity (S) and chlorophyll (chl-a) the correlation analysis,, TDN and DON are associated with salinity showed a significant negative correlation between October and most significant correlation . Visible terrestrial runoff on TDN and DON content has an important influence, and with precipitation related. TDN and DON and chlorophyll also showed a negative correlation, but correlation is not obvious, especially in May red tide outbreak period, no significant correlation could be red tide outbreak cycle of organic nitrogen is quickly consumed. April and mid-October, TDN and DON correlation with chlorophyll than surface and bottom. C / N ratio showed a positive correlation with salinity, chlorophyll in May with no obvious correlation, in April and October of the middle positively correlated with chlorophyll.