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Yellow substance in the North Sea : spatial and temporal distribution using absorption spectroscopy

Laar, S. van (1995) Yellow substance in the North Sea : spatial and temporal distribution using absorption spectroscopy. Master's Thesis / Essay, Biology.

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Abstract

Optical remote sensing is used to study parameters related to water colour. The colour data obtained this way can be converted to spatial and temporal distribution patterns of parameters related to water colour. The result of this conversion are quantitative images which can play an important role in calibration and validation of hydrodynamic and ecological models. Yellow substance is one of the important constituents in the water column influencing the water colour. It absorbs light increasingly with decreasing wavelength; in this way it interferes with remotely sensed data of chlorophyll a and suspended matter in the visible domain. Furthermore, yellow substance affects the ecology of water bodies and affects the penetration of UV-light in natural waters. The collection of dark coloured organic compounds of soil and sedimentary accumulations is called yellow substance. The main components are humic and fulvic acids. Most yellow substance in natural waters is of terrestrial origin, but in open oceans yellow substance may also be derived from decomposition products of marine organisms. The residence time of yellow substance in oceans is estimated at 150-900 years; it thus forms a semi-conservative property in the marine environment. In this research absorption spectroscopy was used to measure the spatial and temporal variation in the concentration of yellow substance in the southern North Sea in samples taken in 1993 and 1994. Spectra obtained in this way are exponential and can be described by two parameters, the absorption coefficient at a reference wavelength, normally 380 nm, and the slope of the exponential. The absorption coefficients decreased from on-shore to off-shore stations. The highest coefficients for the absorption by yellow substance were found at the Texel transect, high coefficients were also found at the on-shore stations of the Noordwijk and Walcheren transects and at the Marsdiep station. In the Channel the lowest coefficients were measured, at many off-shore stations low coefficients were also obtained. The output of rivers was clearly •the main source of yellow substance in the North Sea. Especially at the on-shore stations this influence was very large, but other factors such as origin of water masses may play a role too. The content of yellow substance from the several rivers discharging into the North Sea depends on the characteristics of the catchment area, such as forests, agricultural land and cities, of these rivers. Yellow substance concentration and salinity had a strong negative correlation. Chlorophyll a and suspended matter, however, did not show any correlation with yellow substance. Although degradation of phytoplankton results in yellow substance, the yellow substance component of the water due to degradation of marine organisms is very small relative to the riverine input. The values for the slope, calculated for the whole absorption spectrum of yellow substance, were higher than values. This is due to the tendency of the spectra to increase at lower wavelengths. A bump at 275 nm, which is thought to be the result of absorption by dissolved DNA, is another reason for the increase of the slope. If the slope is calculated for segments (360-440 nm and 440-540 nm) of the spectrum, measured values were in the same range as the values in previous research.

Item Type: Thesis (Master's Thesis / Essay)
Degree programme: Biology
Thesis type: Master's Thesis / Essay
Language: English
Date Deposited: 15 Feb 2018 07:48
Last Modified: 15 Feb 2018 07:48
URI: http://fse.studenttheses.ub.rug.nl/id/eprint/10099

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