RESEARCH ARTICLE Environmental changes affecting light climate in oligotrophic mountain lakes: the deep chlorophyll maxima as a sensitive variable Beatriz Modenutti • Esteban Balseiro • Marcela Bastidas Navarro • Cecilia Laspoumaderes • Marı ´a Sol Souza • Florencia Cuassolo Received: 21 August 2012 / Accepted: 1 November 2012 / Published online: 10 November 2012 Ó Springer Basel 2012 Abstract The North-Patagonian Andean lakes of Argentina are high light, low nutrient environments that exhibit development of deep chlorophyll maxima (DCM) at the metalimnetic layer during summer stratification, at approximately 1 % of surface PAR irradiance. We exam- ined whether the position of DCM changes as a consequence of long-time (global warming: glacial clay input) and short-time (eruption: volcanic ashes) events. We performed different field studies: (1) an interlacustrine analysis of six lakes from different basins, including data of the 2011 volcanic eruption, which caused an unexpected variation in water transparency; and (2) an intralacustrine analysis in which we compared different stations along a transparency gradient in Lake Mascardi caused by glacial clay input at one end of the gradient. In these analyses, we documented changes in DCM depth and its relationship with different parameters. DCM development was not related with thermocline depth or nutrient distribution. In all cases, the only significant variables were Kd 320 nm and Kd PAR. Our study showed that suspended particles (glacial clay and volcanic ashes) can play a crucial role in transparent lakes, affecting lake features such as the phototrophic biomass distribution along the water column. Suspended solid inputs from either glacial clay or volcanic ashes produce a comparable effect, provoking a decrease in light and, consequently, an upper location of the DCM. Thus, the DCM position is highly sensitive to global changes, such as increased temperatures causing glacier recession or to regional changes caused by volcanic eruptions. Keywords Light climate Á Lakes Á Chlorophyll distribution Á Transparent lakes Á Climate change Á Total suspended solids Introduction Water resources are one of the most highly sensitive environmental components, and they can be affected by changes in temperature and precipitation and by the amount of suspended particles and dissolved substances. Lakes and reservoirs have recently been suggested as effective sentinels, integrators, and regulators of climate change (Williamson et al. 2009). Lakes and reservoirs can provide valuable information on the patterns and mecha- nisms of how global climate change is altering ecosystems (Williamson et al. 2008). In alpine regions, changes in glacier length are widely recognized as the most reliable and easily observed indi- cator of climate change (Paul et al. 2007). Because warming affects glacial melting and meltwater carries high amounts of suspended sediments, changes in this input influence water transparency through the attenuation of all wavelengths, including UVR (Hessen 2002; Helbling and Zagarese 2003). However, climate change has also been suggested to influence factors such as the dissolved organic matter (DOM) input to lakes (Schindler and Curtis 1997; Zhang et al. 2010; Couture et al. 2012). Differences in DOM concentrations and, more important, in the optical features of chromophoric dissolved organic matter (CDOM) can cause wide variations in UV attenuation (Williamson and Rose 2010). In addition, geological events B. Modenutti (&) Á E. Balseiro Á M. Bastidas Navarro Á C. Laspoumaderes Á M. S. Souza Á F. Cuassolo Laboratorio de Limnologı ´a, INIBIOMA, UNComahue-CONICET, Quintral 1250, 8400 Bariloche, Argentina e-mail: bmodenutti@comahue-conicet.gob.ar Aquat Sci (2013) 75:361–371 DOI 10.1007/s00027-012-0282-3 Aquatic Sciences 123