Differences in UV transparency and thermal structure between alpine and subalpine lakes: implications for organisms

Abstract

Ultraviolet (UV) radiation is a globally important abiotic factor influencing ecosystem structure and function in multiple ways. While UV radiation can be damaging to most organisms, several factors act to reduce UV exposure of organisms in aquatic ecosystems, the most important of which is dissolved organic carbon (DOC). In alpine lakes, very low concentrations of DOC and a thinner atmosphere lead to unusually high UV exposure levels. These high UV levels combine with low temperatures to provide a fundamentally different vertical structure to alpine lake ecosystems in comparison to most lowland lakes. Here, we discuss the importance of water temperature and UV transparency in structuring alpine lake ecosystems and the consequences for aquatic organisms that inhabit them. We present transparency data on a global data set of alpine lakes and nearby analogous subalpine lakes for comparison. We also present seasonal transparency data on a suite of alpine and subalpine lakes that demonstrate important differences in UV and photosynthetically active radiation (PAR, 400-700 nm) transparency patterns even within a single region. These data are used to explore factors regulating transparency in alpine lakes, to discuss implications of future environmental change on the structure and function of alpine lakes, and ways in which the UV transparency of these lakes can be used as a sentinel of environmental change.

Synergistic effects of UVR and simulated stratification on commensalistic phytoplankton–bacteria relationship in two optically contrasting oligotrophic Mediterranean lakes

“…This would increase the amount of allochthonous dissolved organic matter (DOM) reaching inland and coastal aquatic ecosystems, reducing the penetration of incident UVR (Rose et al, 2009). The UVR filtering characteristics of colored DOM (CDOM) result in a more effective attenuation of shorter (UV-B) than longer (UV-A, 315-400 nm) wavelengths, as also observed for stratospheric ozone.…”

Toward a more comprehensive theory of zooplankton diel vertical migration: Integrating ultraviolet radiation and water transparency into the biotic paradigm

“…In some of the world's most transparent waters, studies based on the diffuse attenuation coefficients (K d ) in surface waters and the assumption that water transparency is constant across depths suggest that UV-A may penetrate to depths approaching 100 m or more. For example, these estimates suggest that Z 1%380nm may reach as deep as 98 m in Lake Tahoe, California and Nevada (Rose et al 2009b); over 100 m in Crater Lake, Oregon (Hargreaves et al 2007); and to 200 m in Lake Vanda, Antarctica (Vincent et al 1998).…”

“…Corresponding reductions in DOC with increasing elevation make alpine lakes some of the highest UV exposure environments on Earth. For example, in a survey of 22 alpine lakes from different regions of the world, the Z 1%380nm averaged 15 m and ranged as deep as 78 m, while the Z 1%380nm values in nearby less transparent subalpine lakes averaged 4.3 m and ranged as deep as 11.8 m (Rose et al 2009a). In some of the world's most transparent waters, studies based on the diffuse attenuation coefficients (K d ) in surface waters and the assumption that water transparency is constant across depths suggest that UV-A may penetrate to depths approaching 100 m or more.…”

“…In aquatic studies, UV is most commonly divided into the shortest, most damaging wavelength UV-B (280-320 nm) and the longer wavelength UV-A (320-400 nm; Williamson and Neale 2009). UV-A generally penetrates to about twice the depth of the more damaging UV-B wavelengths, though in the clearest of lakes, UV-A can penetrate as far as visible light (Rose et al 2009b;Williamson and Neale 2009;Williamson and Rose 2010). Of key importance are the widespread observations that UV can penetrate to biologically significant depths in many marine waters (Tedetti and Sempéré 2006) as well as more transparent inland waters, including boreal lakes (Scully and Lean 1994), temperate glacial lakes in the northern and southern hemispheres (Morris et al 1995), alpine lakes (Laurion et al 1997;Rose et al 2009a), Antarctic lakes (Vincent et al 1998), and lakes in New Zealand (Rae et al 2001) and Japan .…”

Networked lake science: how the Global Lake Ecological Observatory Network (GLEON) works to understand, predict, and communicate lake ecosystem response to global change

“…Through experience and the documentation of what and who is present and in what numbers, we describe and begin to catalog the structure or "state" of an ecosystem as a basis for understanding its ecology, or "process." For example, GLEON scientists have documented the distribution and morphometry of lakes in Argentina (Bohn et al 2011) and water clarity across altitudinal gradients (Rose et al 2009). The paucity of descriptive studies within GLEON does not relegate the importance of natural history to the past, but rather reflects the emphasis on process-based studies more consistent with the technological origins of GLEON.…”