The attenuation of ultraviolet and visible radiation in Dutch inland waters

The vertical attenuation coefficients (K_d) of downward ultraviolet (UV) and visible irradiance (PAR) were measured in 19 different inland waters in the Netherlands using a scanning spectroradiometer. Water chemistry variables such as dissolved organic carbon (DOC), absorbance of dissolved matter (a_d), chlorophyll-a, and particulate matter were measured to determine the relative contribution of dissolved and particulate components in explaining the variation in K_d. In addition to the field measurements, laboratory measurements were performed to test the relationships between water properties and light attenuation. The attenuation properties of Dutch inland waters vary. In most systems the penetration of UV-B radiation (280–320 nm) is limited to the upper decimetres. Lake Maarsseveen was the clearest waterbody in this study, with K_dUVB of 9.1 (m^–1). The DOC concentration had limited power in predicting UV attenuation in this study (r²=0.33), because of the large differences in carbon-specific absorption. A_d300 was a much better predictor of UV attenuation (r²=0.75). The relationships obtained in the laboratory experiments can be used to give a good prediction of in situK_d values, based on 3 variables (chlorophyll-a, ash weight, and absorption of dissolved matter).