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| 2. |
- Kutser, Tiit, et al.
(författare)
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Variations in colored dissolved organic matter between boreal lakes studied by satellite remote sensing
- 2009
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Ingår i: Journal of Applied Remote Sensing. - : SPIE-Intl Soc Optical Eng. - 1931-3195. ; 3, s. 033538-
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Tidskriftsartikel (refereegranskat)abstract
- Therehave been major improvements in our understanding of the roleof lakes and impoundments in global carbon cycle. Estimating thetrue role of lakes as sentinels, regulators and integrators ofclimate change requires analyzing carbon content of vast number oflakes. This is not realistic without using remote sensing methods.There are no satellite sensors at the moment that providefull global coverage and at the same time have spatialand radiometric resolutions suitable for lake color dissolved organic matter(CDOM) mapping. Therefore, the global study has to be performedusing more sensitive sensors to create regional lake CDOM statisticsfor as many sites as possible and extrapolating the resultson global lake map that can be created from lesssensitive sensor data with full global coverage (Landsat). As afirst step towards the global lake carbon mapping we showthat the Advanced Land Imager (ALI) allows to study regionalvariations in lake CDOM content and consequently estimate closely correlatedDOC (dissolved organic carbon) and CO2 saturation values. The resultsshow also that there may be regional differences in lakeCDOM content even if the study sites are geographically relativelyclose to each other and occupying zones with similar landcover and annual runoff. In one occasion the difference canbe explained with human impact that has caused acidification oflakes but the other occasion needs further studies.
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| 3. |
- Markensten, Hampus, 1967-
(författare)
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Climate Effects on Phytoplankton Biomass and Functional Groups
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Future climate in temperate regions is projected to get warmer and in many cases wetter. This poses questions about how phytoplankton in our lakes will respond. A dynamic modeling approach based on an allometric description of phytoplankton characteristics was used to investigate how the biomass of different functional groups of phytoplankton will respond to a changed future climate. Simulations based on a warmer future climate scenario suggest that we will experience an increase in phytoplankton biomass in northern temperate lakes. Moreover, phytoplankton groups are projected to shift towards a dominance of cyanobacteria at the expense of diatoms. Climate may affect phytoplankton, either via in-lake changes in temperature and stratification, or due to altered processes at the watershed level, which influence rates of nutrient export and water discharge. This study found that changes in lake temperature and stratification are the major causes of the projected increase in phytoplankton biomass, but that changes in the timing of nutrient export did influence the succession of diatoms. Variation in SPIM (suspended particulate inorganic matter) can have an important role in influencing the depth of the euphotic zone in a turbid lake, and hence the light climate experienced by phytoplankton. Wind and river discharge were found to regulate SPIM in this study, not only wind as in many other studies. Variations in SPIM could be adequately described by a few governing equations. This thesis suggests that, as a result of climate change, lakes close to the limit of becoming eutrophied may be pushed past a threshold beyond which water quality problems will become more prevalent. Finally it is important to bear in mind that all models are simplifications of the reality as we understand it. Still, the use of models can often give a good indication as to what might be expected in the future.
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| 4. |
- Markensten, Hampus, et al.
(författare)
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Weather driven influences on phytoplankton succession in a shallow lake during contrasting years : Application of PROTBAS
- 2007
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Ingår i: Ecological Modelling. - : Elsevier BV. - 0304-3800 .- 1872-7026. ; 207:2-4, s. 128-136
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Tidskriftsartikel (refereegranskat)abstract
- A dynamic model which simulates variations in the biomass of several phytoplankton functional groups (PROTECH) has been reconstructed into the PROTBAS (PROTech Based Algal Simulations) model, and was tested in a large (61 km(2)), shallow (mean depth 3.4 m) windexposed lake basin at the western end of Lake Malaren, Sweden. A subroutine was added to the model to estimate the variation in light extinction resulting from wind action and river discharge. Also the rate of regeneration of nitrogen and silica was modified. The model captured the overall magnitude and succession of phytoplankton during two contrasting years: a warm and calm calibration year, and a cold windy validation year. The model shows good behavior in the northern temperate climate, which includes ice cover during winter. However, there were discrepancies between measured and modeled spring growth and autumn decline of the phytoplankton.
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| 5. |
- Moore, Karen, 1958-
(författare)
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Climate Change Impacts on the Catchment Contribution to Lake Water Quantity and Quality
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- A key question related to climate change projections is how will aquatic systems respond to changes in variables such as temperature and precipitation? This thesis uses GWLF, a simple catchment scale model to explore potential impacts of climate change on water quantity and quality.River discharge and nutrient loads were modelled for several warmer world scenarios. For one catchment in New York, USA changes in annual dissolved phosphorus loads decreased along with annual streamflow, and particulate phosphorus loads increased for a single future climate scenario. For the Galten catchment of Lake Mälaren, Sweden, the spring melt peak observed historically was reduced for six future scenarios. Peak runoff and dissolved phosphorus and nitrogen load maxima occurred in winter rather than early spring.A synthesis of model results for dissolved inorganic nitrogen (DIN) loadings for five European catchments showed changes in the timing and magnitude of peak DIN load for several future scenarios. In northern Europe, changes were largely due to increased winter streamflow and reduced snow pack and spring melt runoff. In western Europe, DIN loads increased in winter or early spring due to increased precipitation.The biological response for a warmer future scenario was modelled for the Galten basin of Lake Mälaren using GWLF coupled to a lake phytoplankton model and a physical lake model. An increase in cyanobacteria biomass accompanied by a decline in diatom biomass resulted from changes in the timing of nutrient export from the catchment. The projected increase in lake temperature favored an overall increase in total phytoplankton biomass.Lastly, a method based on hourly measurements of colored dissolved organic matter (CDOM) fluorescence provides the appropriate data for dissolved organic carbon (DOC) model parameterization and may also be used for surveillance of organic matter inputs to lakes.
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| 6. |
- Moore, Karen, et al.
(författare)
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Effects of Warmer World Scenarios on Hydrologic Inputs to Lake Mälaren, Sweden and Implications for Nutrient Loads
- 2008
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Ingår i: Hydrobiologia. - : Springer Science and Business Media LLC. - 0018-8158 .- 1573-5117. ; 599, s. 191-199
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Tidskriftsartikel (refereegranskat)abstract
- A simple, rapid, and flexible modelling approach was applied to explore the impacts of climate change on hydrologic inputs and consequent implications for nutrient loading to Lake Malaren, Sweden using a loading function model (GWLF). The first step in the process was to adapt the model for use in a large and complex Swedish catchment. We focused on the Galten basin with four rivers draining into the western region of Malaren. The catchment model was calibrated and tested using long-term historical data for river discharge and dissolved nutrients (N, P). Then multiple regional climate model simulation results were downscaled to the local catchment level, and used to simulate possible hydrological and nutrient loading responses to warmer world scenarios. Climate change projections for the rivers of Galten basin show profound changes in the timing of discharge and nutrient delivery due to increased winter precipitation and earlier snow melt. Impacts on total annual discharge and load are minimal, but the alteration in river flow regime and the timing of nutrient delivery for future climate scenarios is strikingly different from historical conditions.
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| 7. |
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| 8. |
- Pierson, Donald C., et al.
(författare)
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Relationship between the attenuation of downwelling irradiance at 490 nm with the attenuation of PAR (400 nm-700 nm) in the Baltic Sea
- 2008
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Ingår i: Remote Sensing of Environment. - : Elsevier BV. - 0034-4257 .- 1879-0704. ; 112:3, s. 668-680
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Tidskriftsartikel (refereegranskat)abstract
- The vertical attenuation coefficient of diffuse downwelling irradiance at 490 nm (K-d 490) is a parameter that we routinely derive from SeaWiFS images of the Baltic Sea. Here, through model simulations, we examine the relationship between Kd(490), and the vertical attenuation coefficient of PAR (Kd PAR), as this later coefficient determines the light available for aquatic photosynthesis. A simple semi-analytical model is used to predict Kd(490) and Kd(PAR), as a function of the concentrations of chlorophyll, colored dissolved organic material (CDOM), suspended inorganic, and suspended organic particulate material. A series of model simulations based on variations in these optically significant constituents over a range realistic for the Baltic Sea, are used to define the relationship between the two attenuation coefficients. K-d(PAR) = 0.6677K(d)(490)(0.6763). This relationship was verified, using data collected independently from the data set used to derive model coefficients, and appears robust when applied to the Baltic Sea. Comparison to other studies and model sensitivity analyses suggest that the relationship will be dependent on relatively large regional variations in CDOM absorption. A relationship between K-d(490) and Secchi disk depth was also developed and verified. This relationship while useful was more uncertain. The uncertainty was related to a greater influence of scattering on Secchi disk depth estimates and the corresponding parameterization of scattering in our model.
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