Nitrate source identification and quantification in the euphotic zone of the Baltic Proper using nitrogen and oxygen stable isotopes

将利用氮和氧稳定同位素确定和量化波罗的海地区的硝酸盐来源。波罗的海受到集水区（面积是海本身的4倍）和那里的人为活动的强烈影响。特别是通过河流、点源和大气沉积输入的硝酸盐和磷引起富营养化，加剧了底层水域的缺氧。另一个来源是绿藻在绿光区的固氮作用。潜在的硝酸盐来源大部分是已知的。但是，它们的数量和对波罗的海地区天然光区的初级生产的相对重要性仍然存在很大的不确定性。反硝化器方法可以同时测量硝酸盐的氮和氧同位素，将首次在该地区应用。同位素特征可以区分不同的氮源和影响光层中硝酸盐浓度的过程。潜在的来源（硝酸盐库，大气沉积和首次溶解的有机氮）将进行分析。进一步的实验研究将有助于确定不同形式的氮（无机和有机）对初级生产的相对重要性。将建立波罗的海中部光层的硝酸盐预算。

Nitrate sources of the Baltic Proper will be identified and quantified by means of nitrogen and oxygen stable isotopes. The Baltic Sea is strongly influenced by the catchment (covering 4 times the area of the sea itself) and the anthropogenic activity there. In particular nitrate and phosphorus inputs via rivers, point sources, and atmospheric deposition cause eutrophication which aggravate anoxia in bottom waters. An additional source is nitrogen fixation by cyanobacteria in the euphotic zone. Potential nitrate sources are largely known. However, there are still substantial uncertainties regarding their quantity and relative importance for the primary production in the euphotic zone of the Baltic Proper. The denitrifier method, which enables measurement of both nitrogen and oxygen isotopes of nitrate, will be applied for the first time in this region. The isotope signature makes it possible to distinguish between different nitrogen sources and processes affecting the nitrate concentration in the euphotic layer. Potential sources (nitrate pool, atmospheric deposition plus for the first time dissolved organic nitrogen) will be analyzed. Additional experimental studies will help to determine the relative importance of different nitrogen forms (inorganic and organic) supporting the primary production. A nitrate budget for the euphotic layer in the central Baltic Sea will be established.