title: Pronounced chemical response of Subarctic lakes to climate-driven losses in surface area.
abstract: Losses in lake area have been observed for several Arctic and Subarctic regions in recent decades, with unknown consequences for lake ecosystems. These reductions are primarily attributed to two climate-sensitive mechanisms, both of which may also cause changes in water chemistry: (i) increased imbalance of evaporation relative to inflow, whereby increased evaporation and decreased inflow act to concentrate solutes into smaller volumes; and (ii) accelerated permafrost degradation, which enhances sublacustrine drainage while simultaneously leaching previously frozen solutes into lakes. We documented changes in nutrients [total nitrogen (TN), total phosphorus (TP)] and ions (calcium, chloride, magnesium, sodium) over a 25 year interval in shrinking, stable, and expanding Subarctic lakes of the Yukon Flats, Alaska. Concentrations of all six solutes increased in shrinking lakes from 1985-1989 to 2010-2012, while simultaneously undergoing little change in stable or expanding lakes. This created a present-day pattern, much weaker or absent in the 1980s, in which shrinking lakes had higher solute concentrations than their stable or expanding counterparts. An imbalanced evaporation-to-inflow ratio (E/I) was the most likely mechanism behind such changes; all four ions, which behave semiconservatively and are prone to evapoconcentration, increased in shrinking lakes and, along with TN and TP, were positively related to isotopically derived E/I estimates. Moreover, the most conservative ion, chloride, increased >500% in shrinking lakes. Conversely, only TP concentration was related to probability of permafrost presence, being highest at intermediate probabilities. Overall, the substantial increases of nutrients (TN >200%, TP >100%) and ions (>100%) may shift shrinking lakes towards overly eutrophic or saline states, with potentially severe consequences for ecosystems of northern lakes.
authors.affiliation: Department of Biology and Wildlife and Institute of Arctic Biology, University of Alaska Fairbanks, Fairbanks, Alaska, 99775, USA.
authors.forename: Tyler L
authors.initials: TL
authors.lastname: Lewis
authors.forename: Mark S
authors.initials: MS
authors.lastname: Lindberg
authors.forename: Joel A
authors.initials: JA
authors.lastname: Schmutz
authors.forename: Patricia J
authors.initials: PJ
authors.lastname: Heglund
authors.forename: Jennifer
authors.initials: J
authors.lastname: Rover
authors.forename: Joshua C
authors.initials: JC
authors.lastname: Koch
authors.forename: Mark R
authors.initials: MR
authors.lastname: Bertram
mesh_terms: D000413:Alaska; D001110:Arctic Regions; D057231:Climate Change; D004784:Environmental Monitoring; D060106:Lakes / Q000737:chemistry*; D009584:Nitrogen / Q000032:analysis*; D010758:Phosphorus / Q000032:analysis*; D012621:Seasons
chemical_list: D010758:Phosphorus; D009584:Nitrogen
keywords: aquatic nutrients; eutrophication; evapoconcentration; permafrost; shrinking lakes; subarctic; water chemistry