Specific attenuation coefficients of optically active substances and their contribution to the underwater ultraviolet and visible light climate in shallow lakes and ponds

Abstract

Sunlight penetration through the water column is controlled by the amount and kind of materials dissolved and suspended in the water. Understanding UV penetration in its complexity is essential for the prediction of the impact of UV radiation on aquatic ecosystems. However, only limited data are available on the penetration of UVR into shallow waters rich in inorganic suspended solids and chromophoric dissolved organic matter (CDOM). The same is true for the specific attenuation coefficients of light-absorbing components at the UV waveband. This study analyses the role of CDOM, algal-free suspended solids and algae in the formation of underwater UVR and PAR climate in 30 water bodies from clear gravel pit lakes trough the shallow Lake Balaton to turbid soda pans. Irradiance-depth profiles were obtained at 305, 313, 320 nm (UV-B), 340, 380, 395 nm (UV-A) and 400-700 nm (PAR) with a Biospherical PUV-2500 radiometer. Vertical attenuation coefficients (K d ) were calculated. Water samples were taken for the laboratory measurement of the concentration of light-absorbing components: algae as chlorophyll a (CHL), chromophoric dissolved organic matter as colour (CDOM), and algalfree suspended solids (TSS-Alg) parallel with the in situ light measurements. Specific attenuation coefficient values were calculated by multiple regression analysis (n = 140). The obtained specific UV attenuation coefficient values of CHL, CDOM and TSSAlg made it possible to establish light attenuation at different wavelengths based on the knowledge of the concentration of these light-absorbing components.

Unique picoeukaryotic algal community under multiple environmental stress conditions in a shallow, alkaline pan

“…Photosynthetically active radiation (PAR, 400-700 nm) was considered to be 47% of global radiation (Wetzel and Likens 2000). Underwater light intensity was calculated for each mm of the water column using the vertical light attenuation coefficient determined by the empirical formula of V.- Balogh et al (2009) on the basis of the chlorophyll a concentration, total suspended solids and Pt colour. Light attenuation of the ice cover was also taken into account.…”

Seasonal changes in optical properties of two contrasting tropical freshwater systems

“…Moreover, it significantly reduces harmful effects of UV radiation on aquatic organisms (Zhang et al, 2011b). Several studies in temperate aquatic systems have demonstrated the role of CDOM in the light attenuation (Christian and Sheng, 2003;Balogh et al, 2009;Yamaguchi et al, 2013), but the effect of CDOM in tropical systems still requires effort (Obrador and Pretus, 2008) Optical properties in tropical systems duction, which is responsible for the regeneration of nutrients in the water (Lønborg et al, 2010). It also operates in the physical, chemical and biological processes of transport and availability of nutrients and the development of blooms of phytoplankton in eutrophic lakes (Qualls and Richardson, 2003;Coble, 2007;Stedmon et al, 2007) and it is an important component to estimates and effective management of water quality and eutrophication control (Zhang et al, 2011a).…”

Ultraviolet radiation dose calculation for algal suspensions using UVA and UVB extinction coefficients

“…In the case 66 of UVR, recent studies have demonstrated that simple laboratory measurements allow for establishing 67 reliable relationships between concentrations of optically active substances (such as chlorophyll, 68 dissolved organic matter and total suspended solids) and the underwater UVR light climate in natural 69 systems [10]. 70 71 These approaches are based on the theoretical assumption that light passing through a dilute 72 suspension of cells should obey Beer-Lambert's law [10].…”

“…This assured a 139 homogeneous light pathway for UVR from the surface of the liquid to the sensor in the bottom of the 140 beaker for each sample. This method had been previously applied successfully to measure irradiance 141 extinction in a volume of water that was too shallow to use a radiometer [10] and measuring systems were tested (Tab. 1).…”

“…Vertical light attenuation processes 52 result in a decrease of the intensity and changes in the light spectrum. While light attenuation is 53 routinely considered in ecological studies of UVR [10], it is not often considered in ecotoxicity studies 54 using algae or other aquatic organisms [11,12]. In such studies, the responses of organisms are 55 generally related to doses of UV that are calculated using measurements of UV intensity at the surface 56 of experimental vessels or liquid media.…”