Papers by Kaarina Weckström
Ambio, 2004
Successful management of damaged coastal ecosystems requires reliable scientific evidence of thei... more Successful management of damaged coastal ecosystems requires reliable scientific evidence of their past state. Here we demonstrate that the sediment record of biotic indicators can be used to quantitatively reconstruct nutrient concentrations preceding the short time span covered by monitoring records. We generated a diatom-based weighted-averaging partial least squares transfer function model for total dissolved nitrogen with a prediction accuracy of 0.09 microg L(-1) (log10 units). The model was applied to sediment core data from Laajalahti Bay, an urban embayment in Helsinki, Finland, where its performance was validated against a approximately 30 yr record of water-quality data and known land-use changes in the watershed. The model tracked well the trends in the nutrient record, although it underestimated very high nutrient concentrations in this highly impacted embayment. The generally good agreement between the actual and predicted values implies that the approach has considerable potential in assessing background nutrient concentrations in coastal waters.
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Journal of Phycology, 2006
ABSTRACT
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ABSTRACT Two short sediment cores NE and SE of Newfoundland covering the last ca. 100 years were ... more ABSTRACT Two short sediment cores NE and SE of Newfoundland covering the last ca. 100 years were analysed for IP25, a novel chemical tracer for the presence of seasonal sea ice. Instrumental data (air and sea surface temperatures) and sea ice observations are available for the time period covered by these cores enabling the validation of the sediment proxy record. IP25 has previously been used to produce sea ice reconstructions both in the Canadian Arctic and east of Greenland in the Fram Strait and North Icelandic Shelf area over the last millenia. However, studies enabling the comparison with climate-related modern observations are still required to further establish this highly promising proxy. The results from our short cores show 1) significantly higher IP25 concentrations north of Newfoundland, which is consistent with modern sea-ice observations, 2) a good correlation between IP25 and alkenone-based sea surface temperatures (SSTs) from the NE site 3) an overall good agreement between our proxy data, measured air and SST data, and local and regional sea ice extent. Furthermore, the general trends in the IP25 records can also be correlated to the North Atlantic Oscillation (NAO), with a positive NAO indicating colder conditions and more sea ice in the area. These results support the validity of the late-Holocene IP25 record presented, showing increasing sea ice concentrations starting from ca. 1500 cal. yr BP, with clearly less sea ice during recent times.
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Marine Ecology-progress Series, 2005
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Limnology and Oceanography, 2006
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Journal of Quaternary Science, 2012
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Journal of Paleolimnology, 2010
Subarctic and arctic lakes are the focus of many paleolimnological studies, as they are still amo... more Subarctic and arctic lakes are the focus of many paleolimnological studies, as they are still among the least impacted lakes by humans. Hence they provide an excellent setting for studies on long-term climatic variability without the overriding effects of direct anthropogenic perturbation. On the other hand, these ecosystems are highly vulnerable to even moderate anthropogenic influence like long-distance airborne transport
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Journal of Paleolimnology, 2009
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Baltica, 2012
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AMBIO: A Journal of the Human Environment, 2007
Increased nutrient and sediment loading can affect the functioning and biodiversity of coastal ec... more Increased nutrient and sediment loading can affect the functioning and biodiversity of coastal ecosystems. Lacking long-term monitoring data, paleolimnological techniques enable the estimation of habitat and diversity change through time. Using these methods we assessed the effects of eutrophication on diatom community structure and species richness over the past ca. 200 years in coastal waters of the Gulf of Finland. The abundance of planktonic diatoms has increased markedly because of increased eutrophication and turbidity. The loss of benthic habitats resulted in a clear decrease in diatom species richness after a threshold of 400-600 microg L(-1) total dissolved nitrogen; no unimodal pattern between diversity and productivity was observed in our data. The urban sites displayed a marked decrease in species richness starting in the late 19th century with increased urbanization. A clear recovery was visible after the cessation of point source loading by the mid-1980s at two sites, whereas at the third site no recovery was detected because of diffuse loading from the large catchment. Changes in the rural sites were minor and did not start until the 1940s.
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AMBIO: A Journal of the Human Environment, 2004
Successful management of damaged coastal ecosystems requires reliable scientific evidence of thei... more Successful management of damaged coastal ecosystems requires reliable scientific evidence of their past state. Here we demonstrate that the sediment record of biotic indicators can be used to quantitatively reconstruct nutrient concentrations preceding the short time span covered by monitoring records. We generated a diatom-based weighted-averaging partial least squares transfer function model for total dissolved nitrogen with a prediction accuracy of 0.09 microg L(-1) (log10 units). The model was applied to sediment core data from Laajalahti Bay, an urban embayment in Helsinki, Finland, where its performance was validated against a approximately 30 yr record of water-quality data and known land-use changes in the watershed. The model tracked well the trends in the nutrient record, although it underestimated very high nutrient concentrations in this highly impacted embayment. The generally good agreement between the actual and predicted values implies that the approach has considerable potential in assessing background nutrient concentrations in coastal waters.
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Nova Hedwigia, 2009
ABSTRACT Chrysophyte resting stages (cysts) were analysed in a sediment core from Längsee, a smal... more ABSTRACT Chrysophyte resting stages (cysts) were analysed in a sediment core from Längsee, a small lake in the Carinthian lowland (Austria) with climate-driven meromixis, spanning the Late Glacial Interstadial (= Greenland Interstadial 1, ca. 14.7 to 12.7 ky BP). Of the 32 cyst types occurring at least once with a minimum of > 1%, six were related to chrysophyte taxa so far. Nine cyst types were described as new to science. Aiming to define ecological preferences, we compared the cyst stratigraphy with pollen and diatom stratigraphies, diatom-inferred total phosphorus (Di-TP) and diatom-inferred mean summer epilimnetic water temperatures (Di-SEWT). Two significant cyst zones corresponded with the two main pollen zones (Betula followed by Pinus), and a change from meso-eutrophic (dominance of Cyclotella ocellata) to oligotrophic conditions (C. comensis dominance). Secondary changes in cyst assemblages may have been triggered by climate fluctuations. In sum, we classified three groups of cyst types: (1) cysts related to meso-eutrophic conditions; (2) cysts related to oligotrophic conditions and/or cold water; (3) cysts with unknown ecological preferences.
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Quaternary Science Reviews, 2014
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Limnology and Oceanography, 2006
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Journal of Quaternary Science, 2012
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Papers by Kaarina Weckström