136 research outputs found
Atmospheric stilling offsets the benefits from reduced nutrient loading in a large shallow lake
As part of a global phenomenon, a 30% decrease in average wind speed since 1996 in southern Estonia
together with more frequent easterly winds resulted in 47% decrease in bottom shear stress in the large
(270 km2), shallow (mean depth 2.8 m), and eutrophic Lake VÔrtsjÀrv. Following a peak in eutrophication pressure
in the 1970sâ80s, the concentrations of total nutrients were declining. Nonmetric Multidimensional Scaling
(NMDS) ordination of a 54-year phytoplankton community composition time-series (1964â2017) revealed
three distinct periods with breaking points coinciding with changes in wind and/or water level. Contrary to
expectations, we detected no decrease in optically active substances that could be related to wind stilling,
whereas phytoplankton biomass showed an increasing trend despite reduced nutrient levels. Here we show how
opening of the âlight niche,â caused by declining amount of suspended sediments, was capitalized and filled by
the light-limited phytoplankton community. We suggest that wind stilling is another global factor, complementary
to climate warming that counteracts eutrophication mitigation in lakes and may provide a challenge to
assessment of the lake ecological status.Main financial support for EMU: European Unionâs Horizon 2020 research and innovation programme Under the Marie SkĆodowska-Curie Action, Innovative Training Networks, European Joint Doctorates.Project name, acronym and grant number: Management of climatic extreme events in lakes and reservoirs for the protection of ecosystem services, MANTEL, grant agreement No 722518.Publication date and, if applicable, length of embargo period: Published as Early View on 07.10.2019, no embargo period.Main financial support for EMU: European Unionâs Horizon 2020 research and innovation programme Under the Marie SkĆodowska-Curie Action, Innovative Training Networks, European Joint Doctorate
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Atmospheric stilling leads to prolonged thermal stratification in a large shallow polymictic lake
To quantify the effects of recent and potential future decreases in surface wind speeds on lake thermal stratification, we apply the one-dimensional process-based model MyLake to a large, shallow, polymictic lake, VÔrtsjÀrv. The model is validated for a 3-year period and run separately for 28 years using long-term daily atmospheric forcing data from a nearby meteorological station. Model simulations show exceptionally good agreement with observed surface and bottom water temperatures during the 3-year period. Similarly, simulated surface water temperatures for 28 years show remarkably good agreement with long-term in situ water temperatures. Sensitivity analysis demonstrates that decreasing wind speeds has resulted in substantial changes in stratification dynamics since 1982, while increasing air temperatures during the same period had a negligible effect. Atmospheric stilling is a phenomenon observed globally, and in addition to recent increases in surface air temperature, needs to be considered when evaluating the influence of climate change on lake ecosystems
Rapid and highly variable warming of lake surface waters around the globe
In this first worldwide synthesis of in situ and satellite-derived lake data, we find that lake summer surface water temperatures rose rapidly (global meanâ=â0.34°C decadeâ1) between 1985 and 2009. Our analyses show that surface water warming rates are dependent on combinations of climate and local characteristics, rather than just lake location, leading to the counterintuitive result that regional consistency in lake warming is the exception, rather than the rule. The most rapidly warming lakes are widely geographically distributed, and their warming is associated with interactions among different climatic factorsâfrom seasonally ice-covered lakes in areas where temperature and solar radiation are increasing while cloud cover is diminishing (0.72°C decadeâ1) to ice-free lakes experiencing increases in air temperature and solar radiation (0.53°C decadeâ1). The pervasive and rapid warming observed here signals the urgent need to incorporate climate impacts into vulnerability assessments and adaptation efforts for lakes.Peer reviewe
Storm impacts on phytoplankton community dynamics in lakes
In many regions across the globe, extreme weather events, such as storms, have increased in frequency, intensity and duration. Ecological theory predicts that such extreme events should have large impacts on ecosystem structure and function. For lake ecosystems, high winds and rainfall associated with storms are linked by short term runoff events from catchments and physical mixing of the water column. Although we have a well-developed understanding of how such wind and precipitation events alter lake physical processes, our mechanistic understanding of how these short-term disturbances 48 translate from physical forcing to changes in phytoplankton communities is poor. Here, we provide a conceptual model that identifies how key storm features (i.e., the frequency, intensity, and duration of wind and precipitation) interact with attributes of lakes and their watersheds to generate changes in a lakeâs physical and chemical environment and subsequently phytoplankton community structure and dynamics. We summarize the current understanding of storm-phytoplankton dynamics, identify knowledge gaps with a systematic review of the literature, and suggest future research directions by generating testable hypotheses across a global gradient of lake types and environmental conditions.Fil: Stockwell, Jason D.. University of Vermont; Estados UnidosFil: Adrian, Rita. Leibniz Institute of Freshwater Ecology and Inland Fisheries; AlemaniaFil: Andersen, Mikkel. Dundalk Institute of Technology; IrlandaFil: Anneville, Orlane. Institut National de la Recherche Agronomique; FranciaFil: Bhattacharya, Ruchi. University of Missouri; Estados UnidosFil: Burns, Wilton G.. University of Vermont; Estados UnidosFil: Carey, Cayelan C.. Virginia Tech University; Estados UnidosFil: Carvalho, Laurence. Freshwater Restoration & Sustainability Group; Reino UnidoFil: Chang, ChunWei. National Taiwan University; RepĂșblica de ChinaFil: De Senerpont Domis, Lisette N.. Netherlands Institute of Ecology; PaĂses BajosFil: Doubek, Jonathan P.. University of Vermont; Estados UnidosFil: Dur, GaĂ«l. Shizuoka University; JapĂłnFil: Frassl, Marieke A.. Griffith University; AustraliaFil: Gessner, Mark O.. Leibniz Institute of Freshwater Ecology and Inland Fisheries; AlemaniaFil: Hejzlar, Josef. Biology Centre of the Czech Academy of Sciences; RepĂșblica ChecaFil: Ibelings, Bas W.. University of Geneva; SuizaFil: Janatian, Nasim. Estonian University of Life Sciences; EstoniaFil: Kpodonu, Alfred T. N. K.. City University of New York; Estados UnidosFil: Lajeunesse, Marc J.. University of South Florida; Estados UnidosFil: Lewandowska, Aleksandra M.. Tvarminne Zoological Station; FinlandiaFil: Llames, Maria Eugenia del Rosario. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - La Plata. Instituto de Investigaciones BiotecnolĂłgicas. Universidad Nacional de San MartĂn. Instituto de Investigaciones BiotecnolĂłgicas; ArgentinaFil: Matsuzaki, Shin-ichiro S.. National Institute for Environmental Studies; JapĂłnFil: Nodine, Emily R.. Rollins College; Estados UnidosFil: NĂ”ges, Peeter. Estonian University of Life Sciences; EstoniaFil: Park, Ho-Dong. Shinshu University; JapĂłnFil: Patil, Vijay P.. US Geological Survey; Estados UnidosFil: Pomati, Francesco. Swiss Federal Institute of Water Science and Technology; SuizaFil: Rimmer, Alon. Kinneret Limnological Laboratory; IsraelFil: Rinke, Karsten. Helmholtz-Centre for Environmental Research; AlemaniaFil: Rudstam, Lars G.. Cornell University; Estados UnidosFil: Rusak, James A.. Ontario Ministry of the Environment and Climate Change; CanadĂĄFil: Salmaso, Nico. Research and Innovation Centre - Fondazione Mach; ItaliaFil: Schmitt, François. Laboratoire dâOcĂ©anologie et de GĂ©osciences; FranciaFil: Seltmann, Christian T.. Dundalk Institute of Technology; IrlandaFil: Souissi, Sami. Universite Lille; FranciaFil: Straile, Dietmar. University of Konstanz; AlemaniaFil: Thackeray, Stephen J.. Lancaster Environment Centre; Reino UnidoFil: Thiery, Wim. Vrije Unviversiteit Brussel; BĂ©lgica. Institute for Atmospheric and Climate Science; SuizaFil: Urrutia Cordero, Pablo. Uppsala University; SueciaFil: Venail, Patrick. Universidad de Ginebra; SuizaFil: Verburg, Piet. 8National Institute of Water and Atmospheric Research; Nueva ZelandaFil: Williamson, Tanner J.. Miami University; Estados UnidosFil: Wilson, Harriet L.. Dundalk Institute of Technology; IrlandaFil: Zohary, Tamar. Israel Oceanographic & Limnological Research; IsraelGLEON 20: All Hands' MeetingRottnest IslandAustraliaUniversity of Western AustraliaUniversity of AdelaideGlobal Lake Ecological Observatory Networ
Palaeoclimate inferred from ÎŽ18O and palaeobotanical indicators in freshwater tufa of Lake Ăntu SinijĂ€rv, Estonia
We investigated a 3.75-m-long lacustrine sediment record from Lake Ăntu SinijĂ€rv, northern Estonia, which has a modeled basal age >12,800 cal yr BP. Our multi-proxy approach focused on the stable oxygen isotope composition (ÎŽ18O) of freshwater tufa. Our new palaeoclimate information for the Eastern Baltic region, based on high-resolution ÎŽ18O data (219 samples), is supported by pollen and plant macrofossil data. Radiocarbon dates were used to develop a core chronology and estimate sedimentation rates. Freshwater tufa precipitation started ca. 10,700 cal yr BP, ca. 2,000 years later than suggested by previous studies on the same lake. Younger Dryas cooling is documented clearly in Lake Ăntu SinijĂ€rv sediments by abrupt appearance of diagnostic pollen (Betula nana, Dryas octopetala), highest mineral matter content in sediments (up to 90 %) and low values of ÎŽ18O (less than â12 â°). Globally recognized 9.3- and 8.2-ka cold events are weakly defined by negative shifts in ÎŽ18O values, to â11.3 and â11.7 â°, respectively, and low concentrations of herb pollen and charcoal particles. The Holocene thermal maximum (HTM) is palaeobotanically well documented by the first appearance and establishment of nemoral thermophilous taxa and presence of water lilies requiring warm conditions. Isotope values show an increasing trend during the HTM, from â11.5 to â10.5 â°. Relatively stable environmental conditions, represented by only a small-scale increase in ÎŽ18O (up to 1 â°) and high pollen concentrations between 5,000 and 3,000 cal yr BP, were followed by a decrease in ÎŽ18O, reaching the most negative value (â12.7 â°) recorded in the freshwater tufa ca. 900 cal yr BP
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