title: Trophic dynamics of shrinking Subarctic lakes: naturally eutrophic waters impart resilience to rising nutrient and major ion concentrations.
abstract: Shrinking lakes were recently observed for several Arctic and Subarctic regions due to increased evaporation and permafrost degradation. Along with lake drawdown, these processes often boost aquatic chemical concentrations, potentially impacting trophic dynamics. In particular, elevated chemical levels may impact primary productivity, which may in turn influence populations of primary and secondary consumers. We examined trophic dynamics of 18 shrinking lakes of the Yukon Flats, Alaska, that had experienced pronounced increases in nutrient (>200 % total nitrogen, >100 % total phosphorus) and ion concentrations (>100 % for four major ions combined) from 1985-1989 to 2010-2012, versus 37 stable lakes with relatively little chemical change over the same period. We found that phytoplankton stocks, as indexed by chlorophyll concentrations, remained unchanged in both shrinking and stable lakes from the 1980s to 2010s. Moving up the trophic ladder, we found significant changes in invertebrate abundance across decades, including decreased abundance of five of six groups examined. However, these decadal losses in invertebrate abundance were not limited to shrinking lakes, occurring in lakes with stable surface areas as well. At the top of the food web, we observed that probabilities of lake occupancy for ten waterbird species, including adults and chicks, remained unchanged from the period 1985-1989 to 2010-2012. Overall, our study lakes displayed a high degree of resilience to multi-trophic cascades caused by rising chemical concentrations. This resilience was likely due to their naturally high fertility, such that further nutrient inputs had little impact on waters already near peak production.
authors: Department of Biology and Wildlife and Institute of Arctic Biology, University of Alaska Fairbanks, Fairbanks, AK, 99775, USA. tlewis@usgs.gov.|US Geological Survey, Alaska Science Center, 4210 University Drive, Anchorage, AK, 99508, USA. tlewis@usgs.gov.
authors: Tyler L
authors: TL
authors: Lewis
authors: US Fish and Wildlife Service, 2630 Fanta Reed Road, La Crosse, WI, 54603, USA.
authors: Patricia J
authors: PJ
authors: Heglund
authors: Department of Biology and Wildlife and Institute of Arctic Biology, University of Alaska Fairbanks, Fairbanks, AK, 99775, USA.
authors: Mark S
authors: MS
authors: Lindberg
authors: US Geological Survey, Alaska Science Center, 4210 University Drive, Anchorage, AK, 99508, USA.
authors: Joel A
authors: JA
authors: Schmutz
authors: US National Park Service, Central Alaska Network, 4175 Geist Road, Fairbanks, AK, 99709, USA.
authors: Joshua H
authors: JH
authors: Schmidt
authors: Department of Biology and Wildlife and Institute of Arctic Biology, University of Alaska Fairbanks, Fairbanks, AK, 99775, USA.
authors: Adam J
authors: AJ
authors: Dubour
authors: US Geological Survey, Earth Resources Observation and Science (EROS) Center, 47914 252nd Street, Sioux Falls, SD, 57198, USA.
authors: Jennifer
authors: J
authors: Rover
authors: US Fish and Wildlife Service, Yukon Flats National Wildlife Refuge, 101 12th Avenue, Room 264, Fairbanks, AK, 99701, USA.
authors: Mark R
authors: MR
authors: Bertram
mesh_terms: D000818:Animals; D004784:Environmental Monitoring; D020387:Food Chain; D060106:Lakes; D010758:Phosphorus; D010839:Phytoplankton
chemical_list: D010758:Phosphorus
keywords: Alaska; Aquatic invertebrates; Eutrophication; Resilience; Waterbirds