Contribution of absorption and scattering to the attenuation of UV and photosynthetically available radiation in Lake Biwa

Abstract

Underwater ultraviolet (UV) attenuation is typically modeled using correlative relationships between UV attenuation and dissolved organic carbon (DOC) concentration or colored dissolved organic matter (CDOM) absorption. Our objective was to validate and extend a biogeooptical model of UV penetration that would take into account total absorption as well as scattering by all components of the water column. Diffuse attenuation coefficients, K d (), for photosynthetically available radiation (PAR) and UV irradiance were measured using a PUV500 radiometer at 13 stations in Lake Biwa, Japan, in late summer. Absorption, a, and scattering, b, were measured at nine PAR wavelengths using an AC-9 absorption-attenuation meter. The average K d (PAR) through the euphotic zone, K dav (PAR), was estimated from the measured inherent optical properties using Kirk's equations derived from Monte Carlo simulations. The modeled K dav (PAR) was strongly correlated with measured K d (PAR) values (r 2 ϭ 0.998), although the model systematically underestimated measured values by Ն15%. The relative contribution of absorption and scattering to UV attenuation was evaluated from measurements of the absorption coefficients, an extrapolation of b into the UV, and Kirk's equations. The UV-absorption coefficients for CDOM and particulate matter were measured spectrophotometrically. There was a close agreement between modeled and measured K d (UV) values (r 2 Ն 0.990). The Lake Biwa data showed that particulate absorption and scattering play significant roles in UV attenuation; on average, absorption by water, CDOM, and particles contributed 1, 66, and 21% respectively to K dav (340), while scattering by particles contributed 11%. At a turbid site (NS9) absorption by water, CDOM, and particles contributed 0.3, 40, and 36% respectively to K dav (340), while scattering contributed the remaining 24%. The model described here integrates the effects of all absorption as well as scattering components and provides a more accurate estimate of underwater UV exposure than previous approaches based on CDOM absorption only.

Impact of particulate and dissolved material on light absorption properties in a High-Altitude Lake in Tibet, China

“…Also, the estimated values of K d (PAR) for Lake Namtso are quite similar to the values found for Lake Puma Yumco (Mitamura et al, 2003) and Lake Taupo (Davies-Colley et al, 1984), but higher than the values found for Lake Tahoe (Rose et al, 2009) and Crater Lake Oregon (Hargreaves et al, 2007), and smaller than the value found for north basin of Lake Biwa (Belzile et al, 2002), as shown in Table 3.…”

“…For the surface samples from Lake Namtso, the mean value of the Chl-a concentration was found to be 0. (Vollenweider, 1982)] and make the results of this study comparable to those of studies in other lakes with very low Chl-a concentration values, such as (see Table 3) Lake Taupo, New Zealand (Belzile et al, 2004), Lake Tahoe, USA (Tahoe Environmental Research Center, 2015), north basin of Lake Biwa, Japan (Belzile et al, 2002), as well as in lakes located The values are shown either as a variation range, where extreme values are separated by '-', and where the mean value, if available, is given in parenthesis. In some cases only one available value is given.…”

“…The symbol 'x' indicates that data were not found. a Belzile et al (2004) b Davies-Colley et al (1984) c Tahoe Environmental Research Center (2015) d Rose et al (2009) e Hargreaves et al (2007) f Belzile et al (2002) g Liu et al (2009) h Mitamura et al (2003) above 4,000 m on the Yungui Plateau, China (Zhang et al, 2010) and Lake Puma Yumco, China , the latter being located on the TP. The low Chla concentrations in Lake Namtso water can be related to harsh environmental conditions with a short growing season [normally from mid-May until midSeptember (Dorji et al, 2013)], low temperatures [average annual temperature of À0.16 C (Kang et al, 2011)], and high UV exposure [UV index above 15 on TP (Norsang et al, 2014)].…”

Changes in the spectral and chemical properties of a water mass passing through extensive macrophyte beds in a large fluvial lake (Lake Saint-Pierre, Québec, Canada)

“…Results were similar for UVA (340 nm). These results are consistent with other studies Vincent et al, 2001;Belzile et al, 2002), including one conducted in Lake Saint-Pierre , indicating the dynamic role of dissolved and particulate matter in UV attenuation.…”

Lessons from Lake Biwa and Other Asian Lakes: Global and Local Perspectives

“…UV attenuation in Lake Biwa was measured by Vincent et al (2001) who found that the penetration of these damaging wavelengths is affected by particulate material as well as by dissolved organic matter. This work was then extended at Lake Biwa by Belzile et al (2002). They developed a general model of UV and PAR attenuation in natural waters that incorporates both scattering as well as absorption.…”