title: Climate-induced changes in lake ecosystem structure inferred from coupled neo- and paleoecological approaches.
abstract: Over the 20th century, surface water temperatures have increased in many lake ecosystems around the world, but long-term trends in the vertical thermal structure of lakes remain unclear, despite the strong control that thermal stratification exerts on the biological response of lakes to climate change. Here we used both neo- and paleoecological approaches to develop a fossil-based inference model for lake mixing depths and thereby refine understanding of lake thermal structure change. We focused on three common planktonic diatom taxa, the distributions of which previous research suggests might be affected by mixing depth. Comparative lake surveys and growth rate experiments revealed that these species respond to lake thermal structure when nitrogen is sufficient, with species optima ranging from shallower to deeper mixing depths. The diatom-based mixing depth model was applied to sedimentary diatom profiles extending back to 1750 AD in two lakes with moderate nitrate concentrations but differing climate settings. Thermal reconstructions were consistent with expected changes, with shallower mixing depths inferred for an alpine lake where treeline has advanced, and deeper mixing depths inferred for a boreal lake where wind strength has increased. The inference model developed here provides a new tool to expand and refine understanding of climate-induced changes in lake ecosystems.
authors.affiliation: Climate Change Institute, University of Maine, Orono, Maine 04469, USA. jasmine.saros@maine.edu
authors.forename: Jasmine E
authors.initials: JE
authors.lastname: Saros
authors.forename: Jeffery R
authors.initials: JR
authors.lastname: Stone
authors.forename: Gregory T
authors.initials: GT
authors.lastname: Pederson
authors.forename: Krista E H
authors.initials: KE
authors.lastname: Slemmons
authors.forename: Trisha
authors.initials: T
authors.lastname: Spanbauer
authors.forename: Anna
authors.initials: A
authors.lastname: Schliep
authors.forename: Douglas
authors.initials: D
authors.lastname: Cahl
authors.forename: Craig E
authors.initials: CE
authors.lastname: Williamson
authors.forename: Daniel R
authors.initials: DR
authors.lastname: Engstrom
mesh_terms: D002170:Canada; D057231:Climate Change; D017377:Diatoms; D017753:Ecosystem; D005580:Fossils; D060106:Lakes; D009584:Nitrogen; D013045:Species Specificity; D013696:Temperature; D013997:Time Factors; D014481:United States
chemical_list: D009584:Nitrogen