Melting Alpine Glaciers Enrich High-Elevation Lakes with Reactive Nitrogen

Abstract

See next page for additional authorsFollow this and additional works at: https://digitalcommons.unl.edu/geosciencefacpub Part of the Earth Sciences CommonsThis Article is brought to you for free and open access by the Earth and Atmospheric Sciences, Department of at DigitalCommons@University of Nebraska -Lincoln. It has been accepted for inclusion in Papers in the Earth and Atmospheric Sciences by an authorized administrator of DigitalCommons@University of Nebraska -Lincoln. Alpine glaciers have receded substantially over the last century in many regions of the world. Resulting changes in glacial runoff not only affect the hydrological cycle, but can also alter the physical (i.e., turbidity from glacial flour) and biogeochemical properties of downstream ecosystems. Here we compare nutrient concentrations, transparency gradients, algal biomass, and fossil diatom species richness in two sets of high-elevation lakes: those fed by snowpack melt alone (SF lakes) and those fed by both glacial and snowpack meltwaters (GSF lakes). We found that nitrate (NO 3 -) concentrations in the GSF lakes were 1-2 orders of magnitude higher than in SF lakes. Although nitrogen (N) limitation is common in alpine lakes, algal biomass was lower in highly N-enriched GSF lakes than in the N-poor SF lakes. Contrary to expectations, GSF lakes were more transparent than SF lakes to ultraviolet and equally transparent to photosynthetically active radiation. Sediment diatom assemblages had lower taxonomic richness in the GSF lakes, a feature that has persisted over the last century. Our results demonstrate that the presence of glaciers on alpine watersheds more strongly influences NO 3 -concentrations in high-elevation lake ecosystems than any other geomorphic or biogeographic characteristic. Melting Alpine Glaciers Enrich High-Elevation Lakes with Reactive Nitrogen

The response of Cladocerans to recent environmental forcing in an Alpine Lake on the SE Tibetan Plateau

“…6) indicate the amelioration of the environment at Moon Lake (a longer growing season due to the longer ice-free period) due to the natural climate recovery. However, the remains of the cold-preferring cladocerans such as, A. harpae and C. sphaericus (Hofmann, 1987) continued to increase which may be related to increased input of snow-melt, which would reducing the surface water temperature of the lake combined with increased growth of littoral vegetation as the growing season lengthened (Whiteside et al, 1978;Saros et al, 2010;Thienpont et al, 2015).…”

“…Cladocera in European and North American alpine lakes are reported to have been influenced by both direct and/or indirect environmental forcing . The rise in temperature potentially alters surface water temperature, the duration of ice-cover period, and the input of catchment snow-melt water in alpine environments (Rühland et al, 2006), all of which can directly influence cladoceran growth and reproduction, and indirectly on their food resources by mobilizing nutrient supply used by primary producers (Kattel et al, 2008;Saros et al, 2010). However, it is difficult to understand the direct and indirect effects of climatic forcing on Moon Lake due to the limited climatic data available for southwest China.…”

“…In particular, over the last two centuries, ecosystems of many high mountain lakes across the world have shown different responses, such as loss of biodiversity and shift in biological assemblages, due to rapid changes in their physical environment Thienpont et al, 2015). Rise in temperature has also influenced the nutrient dynamics in alpine lakes; for example, regional warming in North America has enhanced nutrient release from the catchment influencing the lacustrine productivity (Saros et al, 2010). A global increase in atmospheric nutrient deposition is also affecting high alpine lake ecosystems (Neff et al, 2008;Wolfe et al, 2001).…”

“…For example, an increased atmospheric nutrient loading has enhanced autochthonous production as well as the altered phytoplankton community structure and dynamics in North American alpine lakes (Elser et al, 2009;Saros et al, 2010;Holtgrieve et al, 2011). The changes in primary productivity in alpine lakes can have considerable implications for the dynamics of primary consumers such as cladoceran zooplankton (Frey, 1988).…”

Thawing glacial and permafrost features contribute to nitrogen export from Green Lakes Valley, Colorado Front Range, USA

“…For example, there may be enhanced weathering and N-mineralization under a warmer climate (Hong et al 2005), leading to increased N export to surface waters (Henriksen and Hessen 1997). In the northern Rockies, Saros et al (2010) report significantly greater nitrate (NO 3 -) concentrations in glacial and snowmelt fed lakes compared to those collecting snowmelt alone. Similarly, Baron et al (2009) report that recent NO 3 -concentration increases in Loch Vale watershed result from melting ice in permafrost and rock glaciers.…”