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Future climate scenarios for phosphorus and nitrogen dynamics in the Gulf of Riga

Future climate scenarios for phosphorus and nitrogen dynamics in the Gulf of Riga. Bärbel Müller-Karulis , Latvian Institute of Aquatic Ecology Juris Aigars , Latvian Institute of Aquatic Ecology

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Future climate scenarios for phosphorus and nitrogen dynamics in the Gulf of Riga

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  1. Futureclimatescenariosforphosphorus and nitrogendynamicsintheGulfofRiga Bärbel Müller-Karulis, LatvianInstitute of AquaticEcology Juris Aigars, LatvianInstituteofAquaticEcology IncolaborationwithJuris Seņņikovs, Laboratory for MathematicalModelling of Environmental and TechnologicalProcesses, Faculty of Physics and Mathematics, University of Latvia Latvian Institute of Aquatic Ecology

  2. Gulf of Rigacharacteristics • Semi-enclosedbasin • Connected to EasternGotlandbasinsurfacewaters • Salinity 5.5 – 6.2 PSU • Shallow: averagedepth 22 m, maximum 56 m • no permamenthalocline, seasonal thermocline, monomicticcirculation • Highfreshwaterand riverine nutrientinput • Regularmonitoringsince 1973 Response to climatechange ?

  3. Mean temperature (period 1973-2008)

  4. Mean oxygen (period 1973-2008)

  5. Modelsetup • Biogeochemicalmodel • phytoplankton, zooplanktonandnutrients • NPZD Boxmodelbasedon Savchuk 2002 • 2 boxes (pelagic, demersal) + sediments • 3 phytoplanktongroups • Zooplankton • NO3, NH4, PO4, O2 • Calibrated to 28-year observationseries • Physicalmodel (1D) • verticaltemperaturedistributionin the GoR • General OceanTurbulenceModel (GOTM) • Coefficients of secondordermodel: Cheng (2002) • Dynamicequation (k-εstyle) for TKE • Dynamicdissipationrateequation Ecosystemresponse Temperaturechange

  6. Climatechangescenario Climate datafrom PRUDENCE. Control: 1961-1990, Scenario A2: 2070-2100 Extradownscaling of RCM data (biascorrectionviahistogramequalisation): relative humidity (used variable td2m) air temperature (used variable t2m) Original RCM data: sea level pressure (used variable MSLP) cloudiness (used variable clcov) wind speed (used variable w10m) wind direction (used variable w10dir) Calculationsmade for Gulf of Riga (50 m), 30 yearperiod, dailyoutputdata – watertemperature

  7. Physical model results – I(mean temperature distribution over depth) Surface T increaseclose to air T increase T increaseby 1,5 (bottom) to 3 (surface) degrees

  8. Physical model results – II(mean daily pycnocline depth and its variation) ... stratificationlastslonger Pycnoclinedevelopsearlier...

  9. Physical model results – III(mean time-depth plots of temperature) Contemporaryclimate ClimatechangescenarioA2

  10. Verticalwaterexchange decreasedverticalwaterexchange

  11. Demersal oxygen – GR mean

  12. Speciessuccession earlierandmorevigorousspringbloom

  13. Speciessuccession largerbiomass of summerspecies

  14. Speciessuccession morecyanobacteria

  15. Pelagicnutrients largerwinterpool earlierdepletion

  16. Demersalnutrients largerdemersalnutrientconcentrationsinsummer

  17. Verticalnutrientflux increaseddemersalconcentrationscompensatestratificationeffect

  18. Nutrientregeneration Pronouncedincreaseinnutrientrecycling!

  19. Denitrification

  20. Nitrate uptake/release (oxygen control)

  21. Ammoniumversusnitraterelease

  22. Mean nitrate (period 1973-2008)

  23. Conclusions • Increaseinphytoplanktongrowthandprimaryproductivitycausedbyincreasednutrientregeneration • Slightlyincreasedwinternutrientconcentrations • Earlier spring bloom (earlier stratification, no ice cover) • Largersummerphytoplanktonbiomass, morecyanobacteriabecause of moreintensivenutrientregeneration • Lower demersal oxygen concentration caused by more stable and longer stratification • Denitrification – open question for future research

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