Light attenuation in the north sea and the Dutch Wadden sea in relation to secchi disc visibility and suspended matter

Abstract The differences between the so-called “vertical” and “physical” attenuation coefficients are discussed. According to several investigators there is a linear relation between the secchi-depth and the “vertical” attenuation coefficient. The observations discussed in this article also demonstrate the existence of a relation between secchi depth and “physical” attenuation coefficient. The relation between the light attenuation and the concentration of suspended particles in the water is discussed. Such relations, experimentally obtained by several investigators, are compared with those obtained here. Observations made in the Wadden Sea give satisfactory results. The attenuation data obtained for the North Sea are more difficult to relate with the concentration of suspended matter, and the relations found deviate from those found for the same area by Joseph . The possibility exists that this is mainly due to a greater amount of organic material in the suspensions dealt with here.