Ninth International Conference on Permafrost ... - IARC Research

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Carbon Gas Fluxes from Contrasting Boreal Lakes During Intensive Rain EventsJessica López BellidoUniversity of Helsinki, Department of Ecological and Environmental Science, Niemenkatu 73, FIN-15140 Lahti, FinlandAnne OjalaUniversity of Helsinki, Department of Ecological and Environmental Science, Niemenkatu 73, FIN-15140 Lahti, FinlandIntroductionThe variability in climate and weather are typicalcharacteristics in the Northern Hemisphere, which by itselfalready has a strong impact in the hydrology and ecology offreshwater ecosystems. Change in climate variables, such astemperature and precipitation, will definitely impact aquaticspecies at various trophic levels and alter the physical andchemical processes that act on and within the lake ecosystem.Nevertheless, not only will the extreme seasonality affectthe aquatic ecosystems, but also their surrounding areas. Forinstance, the Nordic region has a vast variety of terrains whichcontain a significant number and diversity of lakes. Thislinked pathway makes the lakes vulnerable to changes dueto the direct impact from the adjacent terrestrial ecosystem,leading to the reduction or abundance of organic matterwhich, in turn, significantly impacts aquatic production, thatis, agriculture, forestry, and urbanization. Under this processof human disturbance, the flux of gases between land, water,and atmosphere has been radically altered; thus, the increaseof greenhouses gases to the atmosphere, mainly of carbondioxide and methane.At high latitudes, wetlands (i.e., lakes, ponds, andpeatlands) are the key feature of the landscape. Amongwetlands, lakes are the most important areas where radicalchanges in water management or climate can significantlyaffect the quality of human life. On the other hand, lakesthemselves can affect the climate system. Globally, lakes aresupersaturated with CO 2and CH 4(Cole & Caraco 1998).Lakes in Finland have also been shown to be supersaturatedwith these greenhouse gases (Kortelainen 2000). They playan important role, therefore, in the exchange of CO 2and CH 4at the regional and global scale due to the amount of carbonstored in these ecosystems. This is actually a concern dueto the projections in global climate change in Nordic areas,where today’s sinks can be turned into sources of carbondioxide and methane.In this study, we explored CO 2and CH 4fluxes fromtwo lakes with contrasting limnological characteristics insouthern Finland: Lake Ormajärvi, a clear-water lake, andLake Pääjärvi, a humic brown–water system. The mainhypothesis was that the two lakes differ in their carbon gasfluxes, where the humic lake, which processes more organiccarbon of terrestrial origin, shows larger CO 2fluxes, whereasCH 4fluxes were higher from the more eutrophic clearwaterlake. Due to the limnological distinctions supposedlyresulting in differences in timing and intensity of mixingperiods, differences in seasonal flux patterns were examinedas well as their relation to biological carbon uptake andcarbon mineralization in the epilimnion of the pelagic zone.For instance, it was also hypothesized that fluxes from theclear water Lake Ormajärvi are more closely connected toautochthonous carbon uptake, whereas in the brown-waterLake Pääjärvi, the system is fueled more by allochthonouscarbon; thus fluxes and mineralization processes are tiedtogether. Finally, since during the study year 2004 thesummertime precipitation in the area doubled from theordinary 200–220 mm to 413 mm and the extra rain poureddown in four events June–July, the opportunity allowed thestudy of lake response to an extreme weather event.MethodsMeasurements of CO 2and CH 4fluxes were based onsurface water concentrations as well as gas accumulation infloating closed chambers.Primary production was measured by the radiocarbontechnique, using light/dark bottle incubations (Schindleret al. 1972). Plankton community respiration, that is,biological mineralization of organic carbon, was estimatedfrom the consumption of dissolved oxygen. For final results,the rates of oxygen consumption were converted to rates ofCO 2release using a value of one for the respiratory quotient(RQ) (Wetzel & Likens 2000). To facilitate the comparisonbetween the two different lakes, the data from respirationmeasurements as well as primary production were areallyintegrated. Pelagic CO 2net production due to biologicalprocesses was then calculated by subtracting the primaryproduction from the pelagic mineralization.Results and DiscussionBoth lakes presented seasonalities in fluxes, so thegases accumulated under ice and in the hypolimnion wereventilated out in spring and autumn. The annual CO 2fluxesfrom Lake Ormajärvi and Lake Pääjärvi were 3.6 mol m -2y -1 and 6.1 mol m -2 y -1 , respectively, and both lakes acted asa source of CO 2. The corresponding values for CH 4were24.5 mmol m -2 y -1 and 18.5 mmol m -2 y -1. In terms of globalwarming potential on annual basis, CH 4had contributed7.4% and 19.0% in Lake Pääjärvi and in Lake Ormajärvi,respectively.The most distinctive results of this study were theoverwhelming importance of rain events to gas fluxes. InLake Pääjärvi, the high precipitation resulted in a large peakin CO 2and CH 4fluxes which lasted for a couple of weeks andcontributed to 46% in CO 2and 48% in CH 4annual fluxes.In Lake Ormajärvi, the contribution of the rainy periodto carbon gas fluxes was 39% and 37% for CH 4and CO 2,respectively. The response of Lake Ormajärvi fluxes to high191
Ni n t h In t e r n at i o n a l Co n f e r e n c e o n Pe r m a f r o s tprecipitation was not as sudden and immediate as in LakePääjärvi, but the outcome was more radical, since before therainy period the lake was autotrophic; that is, photosynthesisexceeded respiration. When the rains started, however,the lake turned to heterotrophy with respiration exceedingphotosynthesis. Opposite to Lake Ormajärvi, Lake Pääjärviappeared net heterotrophic throughout the study period. Bythoroughly analyzing the results on biological processeswithin the lakes, the “extra” CO 2and CH 4did not originatefrom mineralization processes within the lakes, but the gaseswere flushed into the lakes from the surrounding terrestrialsoil and were of allochthonous origin.ConclusionThis study demonstrated that the link between thecatchment and the lake is more immediate than anticipatedand is strongly controlled by hydrology. Also, the role ofinput of CO 2and CH 4can be significant even in summertime,when there is an extreme rainfall event. In northern Europe,these kinds of high extremes of precipitation are very likely toincrease in magnitude and frequency due to climate change.Thus, for correct estimates of carbon exchange of terrestrialecosystems, the role of lakes as efflux sites of carbon gasesof terrestrial origin should be taken into account.AcknowledgmentsFinancial support was provided by NECC (Nordic Centerof Excellence for Studies of Ecosystem Carbon Exchangeand its Interactions with Climate Ecosystem). Thanksare also to Lammi Biological Station of the University ofHelsinki.ReferencesCole, J.J. & Caraco, N.F. 1998. Atmospheric exchangeof carbon dioxide in low-wind oligotrophic lakemeasured by the addition of SF 6. Limnol. Oceanogr.43: 647-656.Kortelainen, P., Huttunen, J., Väisänen, T., Mattsson, T.,Karjalainen, P. & Martikainen, P. 2000. CH 4, CO 2and N 2O supersaturation in 12 Finnish lakes beforeand after ice melt. Verh. Int. Ver. Limnol. 27(3): 1410-1414Schindler, D.W., Schmidt, R.V. & Reid, R. 1972. Acidificationand bubbling as an alternative to filtration indetermining phytoplankton production by the 14 Cmethod. J. Fish. Res. Board Can. 29: 1627-1631.Wetzel, R.G. & Likens, G. 2000. Limnological Analyses, 2 nded. New York, NY: Springer Verlag.90807060504030201001st Qtr2ndQtr3rd Qtr4th QtrEastWestNorthFigure 1. CO 2net production and community respiration in relationto ∆CO 2flux in (A) Lake Pääjärvi and (B) Lake Ormajärvi. Theperiod of heaviest rains is shown with arrows. The inserts displayR:PP ratios in both lakes.192
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ContentsPreface ...................
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Mapping and Modeling the Distributi
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Satellite Observations of Frozen Gr
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xiiIce Wedge Thermal Regime in Nort
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xivPermafrost Response to Dynamics
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NICOP SponsorsUniversitiesUniversit
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Deep Permafrost Studies at the Lupi
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Effect of Fire on Pond Dynamics in
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Cryological Status of Russian Soils
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Acoustical Surveys of Methane Plume
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Permafrost Delineation Near Fairban
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Preparatory Work for a Permanent Ge
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A Provisional Soil Map of the Trans
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Martian Permafrost Depths from Orbi
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Time Series Analyses of Active Micr
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Impact of Permafrost Degradation on
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DC Resistivity Soundings Across a P
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Modeling Thermal and Moisture Regim
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A Provisional Permafrost Map of the
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Alpine Permafrost Distribution at M
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Cryogenic Formations of the Caucasu
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Modeling Potential Climatic Change
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A Hypothesis: A Condition of Growth
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Modeled Continual Surface Water Sto
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Freeze/Thaw Properties of Tundra So
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Discontinuous Permafrost Distributi
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Thermal Regime Within an Arctic Was
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Seasonal and Interannual Variabilit
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Twelve-Year Thaw Progression Data f
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Continued Permafrost Warming in Nor
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Landsliding Following Forest Fire o
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A Permafrost Model Incorporating Dy
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Seasonal Sources of Soil Respiratio
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Greenland Permafrost Temperature Si
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The Importance of Snow Cover Evolut
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The Account of Long-Term Air Temper
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The Combined Isotopic Analysis of L
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Adaptating and Managing Nunavik’s
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Human Experience of Cryospheric Cha
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HiRISE Observations of Fractured Mo
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A Soil Freeze-Thaw Model Through th
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Mapping and Modeling the Distributi
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First Results of Ground Surface Tem
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Historical Changes in the Seasonall
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Rock Glaciers in the Kåfjord Area,
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Snowpack Evolution on Permafrost, N
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Climate Change in Permafrost Region
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Maximizing Construction Season in a
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Pleistocene Sand-Wedge, Composite-W
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