Browsing by Subject "Lakes"

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  • Poikane, Sandra; Birk, Sebastian; Boehmer, Juergen; Carvalho, Laurence; de Hoyos, Caridad; Gassner, Hubert; Hellsten, Seppo; Kelly, Martyn; Solheim, Anne Lyche; Olin, Mikko; Pall, Karin; Phillips, Geoff; Portielje, Rob; Ritterbusch, David; Sandin, Leonard; Schartau, Ann-Kristin; Solimini, Angelo G.; van den Berg, Marcel; Wolfram, Georg; van de Bund, Wouter (2015)
    The Water Framework Directive is the first international legislation to require European countries to establish comparable ecological assessment schemes for their freshwaters. A key element in harmonising quality classification within and between Europe's river basins is an "Intercalibration" exercise, stipulated by the WFD, to ensure that the good status boundaries in all of the biological assessment methods correspond to similar levels of anthropogenic pressure. In this article, we provide a comprehensive overview of this international comparison, focusing on the assessment schemes developed for freshwater lakes. Out of 82 lake ecological assessment methods reported for the comparison, 62 were successfully intercalibrated and included in the EC Decision on intercalibration, with a high proportion of phytoplankton (18), macrophyte (17) and benthic fauna (13) assessment methods. All the lake assessment methods are reviewed in this article, including the results of intercalibration. Furthermore, the current gaps and way forward to reach consistent management objectives for European lakes are discussed. (C) 2015 The Authors. Published by Elsevier Ltd.
  • Guseva, S.; Armani, F.; Desai, A. R.; Dias, N. L.; Friborg, T.; Iwata, H.; Jansen, J.; Lükő, G.; Mammarella, I; Repina, I.; Rutgersson, A.; Sachs, T.; Scholz, K.; Spank, U.; Stepanenko, V.; Torma, P.; Vesala, T.; Lorke, A. (2023)
  • Tang, Mingguang; Li, Zhijun; Lu, Peng; Cao, Xiaowei; Li, Guoyu; Leppäranta, Matti; Arvola, Lauri; Shi, Lijuan (2020)
    Based on the features of diurnal variation of ice surface albedo in the Lake Ulansuhai, the relationship between solar elevation angle and geographic coordinates and Julian days, together with normalized time, to express the diurnal variations of the ice albedo. Linear combinations of four probability density distribution functions with exponential forms, including Laplace, Gauss, Gumbel, and Cauchy equations, were used to simulate the diurnal variations in observed ice albedo from sunrise to sunset with solar elevation angle more than 5°. The results reveals that the Laplace combined statistical model is the best fit to the observations. It can not only clearly show the double-peak distribution in the diurnal variation in ice surface albedo when the elevation angle is greater than 5°, but also express the U-type distribution between the two peaks as the elevation angle is more than 15°. This model has advantages of simple form in expression and clear physical meaning. The length parameter is close to half day, and the peak location is associated with the time of sunrise, and the asymmetry of the two peaks can be also shown. It provides a solid foundation for the parameterization schemes on the diurnal variations in lake ice surface albedo in different regions. © 2020 by Journal of Lake Sciences.
  • Golub, Malgorzata; Koupaei-Abyazani, Nikaan; Vesala, Timo; Mammarella, Ivan; Ojala, Anne; Bohrer, Gil; Weyhenmeyer, Gesa A.; Blanken, Peter D.; Eugster, Werner; Koebsch, Franziska; Chen, Jiquan; Czajkowski, Kevin; Deshmukh, Chandrashekhar; Guerin, Frederic; Heiskanen, Jouni; Humphreys, Elyn; Jonsson, Anders; Karlsson, Jan; Kling, George; Lee, Xuhui; Liu, Heping; Lohila, Annalea; Lundin, Erik; Morin, Tim; Podgrajsek, Eva; Provenzale, Maria; Rutgersson, Anna; Sachs, Torsten; Sahlee, Erik; Serca, Dominique; Shao, Changliang; Spence, Christopher; Strachan, Ian B.; Xiao, Wei; Desai, Ankur R. (2023)
    Accounting for temporal changes in carbon dioxide (CO2) effluxes from freshwaters remains a challenge for global and regional carbon budgets. Here, we synthesize 171 site-months of flux measurements of CO2 based on the eddy covariance method from 13 lakes and reservoirs in the Northern Hemisphere, and quantify dynamics at multiple temporal scales. We found pronounced sub-annual variability in CO2 flux at all sites. By accounting for diel variation, only 11% of site-months were net daily sinks of CO2. Annual CO2 emissions had an average of 25% (range 3%-58%) interannual variation. Similar to studies on streams, nighttime emissions regularly exceeded daytime emissions. Biophysical regulations of CO2 flux variability were delineated through mutual information analysis. Sample analysis of CO2 fluxes indicate the importance of continuous measurements. Better characterization of short- and long-term variability is necessary to understand and improve detection of temporal changes of CO2 fluxes in response to natural and anthropogenic drivers. Our results indicate that existing global lake carbon budgets relying primarily on daytime measurements yield underestimates of net emissions.
  • Horppila, Jukka; Pippingsköld, Ella Sofia Lydia; Estlander, Satu (2022)
    Brownification of lakes is a widely spread environmental problem. Brownification is a severe phenomenon, because water colour strongly shapes lake ecosystems through effects on the physical-chemical environment and biological communities. The effects of brownification on aquatic macrophytes are poorly known. Therefore, the aim of this study was to find out the effects of increasing water colour on the photosynthetic pigment content of the floating-leaved macrophyte Nuphar lutea. Field data on water quality and pigment content of N. lutea were collected from 27 lakes in southern and central Finland. The concentration of chlorophyll a+b in the floating laminae or in the petioles was not dependent on water colour, but the depth where the maximum chlorophyll a+b concentration was observed in the petioles, decreased with increasing water colour. Chlorophyll a:b ratio in the petioles and in the floating laminae decreased with increasing water colour. The response of the laminae was explained by decreased upward irradiance of light in high-colour lakes. However, the decreasing light intensity along increasing water colour could not alone explain the variations in chlorophyll a:b. The effects of water colour on the spectral composition of light probably also had a regulatory role. The results showed that the effects of lake brownification on pigments of macrophytes may not be limited to submerged species, but floatingleaved species can also be affected, with consequences for their photosynthesis.
  • Tammeorg, Olga; Haldna, Marina; Noges, Peeter; Appleby, Peter; Mols, Tonu; Niemisto, Juha; Tammeorg, Priit; Horppila, Jukka (2018)
    Phosphorus retention (TPacc) is one of the major water quality regulators in lakes. The current study aimed at ascertaining the specific lake characteristics regulating TPacc. Moreover, we were interested whether NAO (North Atlantic Oscillation), a proxy of climatic forcing, can explain variability in TPacc, additionally to that ascribed to lake characteristics. Sediment cores were obtained from 21 Finnish lakes, subject to radiometric dating and measurements of TP concentrations. Principal components (PCs) were generated using lake characteristics that are usually included into the modelling of TPacc (e.g. lake area, lake depth, catchment area, P inflow) but also the parameters that the classical models usually missed (e.g. anoxic factor). We used significant principal components (PCs), specific combinations of lake characteristics and monthly NAO values as predictors of TPacc. Lake characteristics explained the bulk of TPacc variability. The most influential factors (positive drivers) behind TPacc included PC1 (representing mainly deep lakes), PC2 (small lakes with high levels of anoxia and water column stability), PC3 (productive lakes with large catchment area and short water residence time), PC4 (lakes with high water column stability, low anoxic factor and relatively high sediment focusing) and PC5 (lakes with high levels of P inflow, anoxia and long water residence time). Additionally, we found a potential negative effect of NAO in October on the annual TPacc. This NAO was significantly positively related to temperatures in surface and near-bottom water layer (also their difference) in autumn, suggesting the possible implications for the internal P dynamics. Increased mineralization of organic matter is the most likely explanation for the reduced TPacc associated with NAO-driven water temperature increase. The analysis presented here contributes to the knowledge of the factors controlling P retention. Moreover, this spatially and temporally comprehensive sediment data can potentially be a valuable source for modelling climate change implications.
  • Heiskanen, Lauri Ilmari; Tuovinen, Juha-Pekka; Vekuri, Henriikka W; Räsänen, Aleksi; Virtanen, Tarmo; Juutinen, Sari; Lohila, Annalea Katriina; Mikola, Juha; Aurela, Mika (2023)
    The subarctic landscape consists of a mosaic of forest, peatland, and aquatic ecosystems and their ecotones. The carbon (C) exchange between ecosystems and the atmosphere through carbon dioxide (CO2) and methane (CH4) fluxes varies spatially and temporally among these ecosystems. Our study area in Kaamanen in northern Finland covered 7 km(2) of boreal subarctic landscape with upland forest, open peatland, pine bogs, and lakes. We measured the CO2 and CH4 fluxes with eddy covariance and chambers between June 2017 and June 2019 and studied the C flux responses to varying meteorological conditions. The landscape area was an annual CO2 sink of -45 +/- 22 and -33 +/- 23 g C m(-2) and a CH4 source of 3.0 +/- 0.2 and 2.7 +/- 0.2 g Cm-2 during the first and second study years, respectively. The pine forest had the largest contribution to the landscape-level CO2 sink, -126 +/- 21 and -101 +/- 19 g C m(-2), and the fen to the CH4 emissions, 7.8 +/- 0.2 and 6.3 +/- 0.3 g C m(-2), during the first and second study years, respectively. The lakes within the area acted as CO2 and CH4 sources to the atmosphere throughout the measurement period, and a lake located downstream from the fen with organic sediment showed 4-fold fluxes compared to a mineral sediment lake. The annual C balances were affected most by the rainy peak growing season in 2017, the warm summer in 2018, and a heatwave and drought event in July 2018. The rainy period increased ecosystem respiration (ER) in the pine forest due to continuously high soil moisture content, and ER was on a level similar to the following, notably warmer, summer. A corresponding ER response to abundant precipitation was not observed for the fen ecosystem, which is adapted to high water table levels, and thus a higher ER sum was observed during the warm summer 2018. During the heat wave and drought period, similar responses were observed for all terrestrial ecosystems, with decreased gross primary productivity and net CO2 uptake, caused by the unfavourable growing conditions and plant stress due to the soil moisture and vapour pressure deficits. Additionally, the CH(4 )emissions from the fen decreased during and after the drought. However, the timing and duration of drought effects varied between the fen and forest ecosystems, as C fluxes were affected sooner and had a shorter post-drought recovery time in the fen than forest. The differing CO2 flux response to weather variations showed that terrestrial ecosystems can have a contrasting impact on the landscape-level C balance in a changing climate, even if they function similarly most of the time.