Biogeochemical responses of two alpine lakes to climate change and atmospheric deposition, Jasper and Banff National parks, Canadian Rocky Mountains William O. Hobbs, Rolf D. Vinebrooke, and Alexander P. Wolfe Abstract: The sensitivity of remote alpine ecosystems to global change has been documented by 20th century changes in climate, glacial recession, and terrestrial and aquatic ecosystems. Here we present sedimentary records of biogeochemical re- sponses in two alpine lake ecosystems to multiple environmental drivers over the last ∼500 years in Banff and Jasper Na- tional Parks (Alberta, Canada). We combine paleoecological measures of primary production and diatom community structure with geochemical proxies of reactive N (Nr) deposition to describe the nature and rate of recent ecosystem changes. Curator Lake in Jasper shows a strong diatom response to the limnological effects of climate warming (e.g., ther- mal stratification), but little evidence of changes in Nr cycling over the last ∼500 years. The response of McConnell Lake in Banff to climate change is strongly mediated by glacial activity within the catchment and changing inputs of Nr. Our findings highlight the range of limnological responses that may be expressed by similar ecosystems subjected to comparable abiotic stressors, while further documenting the magnitude of the ecological footprint associated with recent environmental change in mountain park environments. Résumé : La sensibilité des écosystèmes alpins éloignés au changement global a été démontrée par les modifications pro- duites au cours du 20 e siècle dans le climat, dans le retrait des glaciers et dans les écosystèmes terrestres et aquatiques. Nous présentons ici des enregistrements sédimentaires de réponses biogéochimiques de deux écosystèmes lacustres alpins aux multiples facteurs de changement du milieu au cours des derniers ∼500 ans dans les parcs nationaux de Banff et de Jas- per (Alberta, Canada). Nous combinons des mesures paléoécologiques de la production primaire et des analyses de structure des communautés de diatomées à des variables géochimiques de remplacement du dépôt de N réactif (Nr) afin de décrire la nature et le taux des changements récents à l'écosystème. Le lac Curator à Jasper montre une forte réponse des diatomées aux effets limnologiques du réchauffement du climat (par ex., la stratification thermique), mais peu d'indications de change- ments dans le recyclage de Nr au cours des derniers ∼500 ans. La réponse du lac McConnell à Banff au changement clima- tique est fortement influencée par l'activité glaciaire au sein du bassin versant et par les apports changeants de Nr. Nos résultats soulignent l'étendue des réponses limnologiques qui peuvent être exprimées par des écosystèmes semblables soumis à des facteurs abiotiques de stress comparables; ils apportent des informations additionnelles sur l'importance de l'empreinte écologique associée au changement récent dans les environnements montagneux des parcs. [Traduit par la Rédaction] Introduction Alpine lakes are both sentinels and integrators of anthropo- genic environmental change, despite their remote locations (Williamson et al. 2009). Profound ecological shifts in the ecosystems of alpine lakes have occurred during the 20th century (Parker et al. 2008; Hobbs et al. 2010a). Cumulative impacts of environmental changes on aquatic systems can be confounded by antagonistic and synergistic interactions among stressors (Vinebrooke et al. 2004). It therefore be- comes necessary to expect synergistic responses of alpine lakes to regionally diffuse stressors such as climate change and the atmospheric deposition of nutrients. However, with a general lack of long term monitoring data on alpine lakes, it is often not possible to decipher how aquatic ecosystems have responded to stressors through time on a decadal to cen- tennial scale. The careful interrogation of lake sediment re- cords, paleolimnology, can be used to provide ecological trends and answers to questions of ecosystem response (Smol 2010). Geochemical and subfossil biological remains of the aquatic ecosystem are generally well preserved in lake sediments. Alpine lakes are well suited for paleolimnological Received 21 September 2010. Accepted 25 March 2011. Published at www.nrcresearchpress.com/cjfas on xx August 2011. J22026 Paper handled by Associate Editor Gesa Antoine Weyhenmeyer. W.O. Hobbs* and A.P. Wolfe. Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, AB T6G 2E3, Canada. R.D. Vinebrooke. Department of Biological Sciences, University of Alberta, Edmonton, AB T6G 2E9, Canada. Corresponding author: William O Hobbs (e-mail: whobbs@smm.org). *Present address: St. Croix Watershed Research Station, 16910 152nd Street North, Marine-on-St. Croix, MN 55047, USA. 1480 Can. J. Fish. Aquat. Sci. 68: 1480–1494 (2011) doi:10.1139/F2011-058 Published by NRC Research Press Can. J. Fish. Aquat. Sci. Downloaded from www.nrcresearchpress.com by University of Alberta on 08/26/11 For personal use only.