Light attenuation characteristics of glacially‐fed lakes

Abstract

Transparency is a fundamental characteristic of aquatic ecosystems and is highly responsive to changes in climate and land use. The transparency of glacially-fed lakes may be a particularly sensitive sentinel characteristic of these changes. However, little is known about the relative contributions of glacial flour versus other factors affecting light attenuation in these lakes. We sampled 18 glacially-fed lakes in Chile, New Zealand, and the U.S. and Canadian Rocky Mountains to characterize how dissolved absorption, algal biomass (approximated by chlorophyll a), water, and glacial flour contributed to attenuation of ultraviolet radiation (UVR) and photosynthetically active radiation (PAR, 400-700 nm). Variation in attenuation across lakes was related to turbidity, which we used as a proxy for the concentration of glacial flour. Turbidity-specific diffuse attenuation coefficients increased with decreasing wavelength and distance from glaciers. Regional differences in turbidity-specific diffuse attenuation coefficients were observed in short UVR wavelengths (305 and 320 nm) but not at longer UVR wavelengths (380 nm) or PAR. Dissolved absorption coefficients, which are closely correlated with diffuse attenuation coefficients in most non-glacially-fed lakes, represented only about one quarter of diffuse attenuation coefficients in study lakes here, whereas glacial flour contributed about two thirds across UVR and PAR. Understanding the optical characteristics of substances that regulate light attenuation in glacially-fed lakes will help elucidate the signals that these systems provide of broader environmental changes and forecast the effects of climate change on these aquatic ecosystems.

Fjord light regime: Bio‐optical variability, absorption budget, and hyperspectral light availability in Sognefjord and Trondheimsfjord, Norway

“…Analysis of spectral 1% light penetration depths therefore allowed a detailed view of nanometer shifts in wavelength along the fjord sections (Figure 8). The shift in the wavelength of maximum penetrating wavelength as a result of increased turbidity upstream is also evident in Richlen et al [2016], wherein a shift from lower (490-502 nm) to higher (536-567 nm) wavelength is reported with decrease in 1% PAR depth in Greenland and Iceland.…”

Distribution and UV protection strategies of zooplankton in clear and glacier-fed alpine lakes

“…As solar radiation is scattered by glacial flour, the UVR attenuation would be underestimated when using the CDOM absorptivity to estimate the K d for turbid lakes. Thus, for the glacier-fed lakes, we used the equation given by Rose and colleagues 47 to calculate the K d from turbidity values. At Lakes FAS3 and FAS4 (summer 2011), in addition, underwater irradiance-depth profiles were taken with a PUV-501B profiler radiometer.…”

Ecological Stoichiometry of the Mountain Cryosphere

“…Glacier-fed streams and lakes reflect the integration of both upstream and in situ processes (Figure 1; Brittain and Milner, 2001;Mindl et al, 2007;Robinson et al, 2016;Hotaling et al, 2017b;Ren and Gao, 2019). Melting glaciers supply key water, sediment, and nutrients to aquatic ecosystems, determining their optical properties, resource availability, and the structure and composition of biological communities (Laspoumaderes et al, 2013;Martyniuk et al, 2014;Rose et al, 2014;Hotaling et al, 2017b;Ren et al, 2017a ; Figures 4, 5). In general, glacier-fed streams and lakes are characterized by considerable sediment input from upstream grinding of bedrock, cold temperatures (e.g., < 10 • even in summer), and dynamic water levels.…”

“…DOC, dissolved organic carbon. regulation of nutrients, temperature, and contaminant inputs (Saros et al, 2010;Slemmons and Saros, 2012;Rose et al, 2014). However, unlike nearby streams, mountain lakes are more likely to be fed by multiple hydrological sources than streams.…”

“…In general, glacier-derived meltwater exhibits higher nitrate concentrations than snowmelt (Hodson, 2006;Wynn et al, 2007;Saros et al, 2010), which in turn leads to more nitrate in primarily glacier-fed vs. snow-fed lakes (Saros et al, 2010;Slemmons and Saros, 2012;Williams et al, 2016;Warner et al, 2017). For example, Williams et al Modenutti et al, 2000;Hodson et al, 2004Hodson et al, , 2005Piwosz et al, 2009;Saros et al, 2010;Slemmons and Saros, 2012;Rose et al, 2014;Salerno et al, 2016), (B) phytoplankton (synthesized from Sterner et al, 1997;Huisman et al, 2004;Mindl et al, 2007;Lami et al, 2010;Slemmons and Saros, 2012;Laspoumaderes et al, 2013Laspoumaderes et al, , 2017, and (C) zooplankton (synthesized from Elser et al, 1996;Sterner and Elser, 2002;Urabe et al, 2002;Laspoumaderes et al, 2013Laspoumaderes et al, , 2017Sommaruga, 2015).…”