Determination of the spectral absorption coefficients of suspended particulate matters in the shallow lakes in the middle and lower reaches of Yangtze River

Abstract

Two methods for measuring absorption coefficients of suspended particulate matters in water were studied and compared.Through the laboratory culturing of typical algae from the shallow lakes in the middle and lower reaches of Yangtze River,the algal particles and the suspension of algae and sediments were determined by Transmittance( T) and Transmittance-Reflectance( T-R)methods,respectively. The measuring stability of the two methods was compared according to the relationships between the spectral absorption coefficients and Chlorophyll-a of the suspended matters. To obtain absorption spectral changes of suspended matters at different levels of turbidity water,the suspension composed of algae and inorganic particles in different concentration gradients were analyzed. The results showed that both T and T-R methods could be applied and have high measurement precisions in pure algae or water containing less inorganic suspended particulate matters. However,the T-R method should be selected for the suspended particulate matter absorption spectra determination in turbid water. This can improve the measurement precision. Considering that the sediments in the study area are susceptible to wind and thus re-suspension,when the inorganic suspended particulate matters in water exceeded 30 mg / L,the T-R method should be selected.