Description: This thesis reports results from a field test of a new, direct and autonomous technique for the measurement of nitrate concentrations at a location in the Kiel Fjord. The method is based on ultraviolet absorption spectrometry (ProPS, TriOS GmbH, Oldenburg, Germany). It is shown that the nitrate analyzer ProPS allows high resolution (0.8 nm) long-term, in-situ, real time mapping of the concentration of the dissolved nitrate at low power consumption in seawater, in-situ and real-time in the range from 0.5 to 200 μmol/L. This method is based on the measurement of sample absorbance at wavelengths from 220 to 360 nm. The instrument has been deployed in a submersible frame at the pier of the Leibniz Institute of Marine Science (IFM-GEOMAR, Kiel, Schleswig-Holstein, Germany) from January 2008 to May 2008 at a fixed depth of 1 m. Additionally a data logger has been used collected the data of temperature, salinity and oxygen. The tests were taken during the 4-month deployment period for a wide range of nitrate concentrations (from 4 to 35 μmol/L). The ultimate goals of this work are improvement and further development of the sensor and the calculation algorithms based on the results from a long-term deployment in the Baltic Sea. Another goal is the investigation of the variation of nitrate concentration of the coastal water. Measurements made in-situ were compared to the laboratory references determined by the colorimetric nitrite method. Several physical parameters e.g. wind direction, wind speed, water level and rainfall are documented for estimation of nitrate variation.