Ultraviolet radiation and bio-optics in Crater Lake, Oregon

Abstract

Crater Lake, Oregon, is a mid-latitude caldera lake famous for its depth (594 m) and blue color. Recent underwater spectral measurements of solar radiation (300-800 nm) support earlier observations of unusual transparency and extend these to UV-B wavelengths. New data suggest that penetration of solar UVR into Crater Lake has a significant ecological impact. Evidence includes a correlation between water column chlorophyll-a and stratospheric ozone since 1984, the scarcity of organisms in the upper water column, and apparent UV screening pigments in phytoplankton that vary with depth. The lowest UV-B diffuse attenuation coefficients (K d,320 ) were similar to those reported for the clearest natural waters elsewhere, and were lower than estimates for pure water published in 1981. Optical proxies for UVR attenuation were correlated with chlorophyll-a concentration (0-30 m) during typical dry summer months from 1984 to 2002. Using all proxies and measurements of UV transparency, decadal and longer cycles were apparent but no long-term trend since the first optical measurement in 1896.

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.…”

“…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)].…”

Exceptional visual clarity and optical purity in a sub‐alpine lake

“…A broadly similar UV spectral trend, measured with an identical PUV instrument, has been reported for Lake Vanda, an Antarctic 'desert' lake (Vincent et al 1998). Crater Lake (Hargreaves et al 2007 andBoss et al 2007) and the center of the Southeast Pacific Gyre (Morel et al 2007) also report even lower UV-blue attenuation. The (good) agreement illustrated in Fig.…”

“…Phytoplankton levels in Blue Lake (Table 1) fig. 10b; Hargreaves et al 2007]) and Lake Vanda (, 0.05 mg m 23 ; Priscu 1995). SPM, POC, and PN concentrations, and flow cytometry particle counts on one occasion, were also extremely low.…”

“…A spectrum from Morel et al (2007) measured in the Southeast Pacific Gyre (their fig. 3) was supplemented with data from Lake Vanda (Vincent et al 1998) and Crater Lake (Hargreaves et al 2007). Symbols represent measurements by filter radiometers.…”