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Papers by Annika Mikomagi
The Anthropocene Review, 2017
Lake sediments constitute natural archives of past environmental changes. Historically, research ... more Lake sediments constitute natural archives of past environmental changes. Historically, research has focused mainly on generating regional climate records, but records of human impacts caused by land use and exploitation of freshwater resources are now attracting scientific and management interests. Long-term environmental records are useful to establish ecosystem reference conditions, enabling comparisons with current environments and potentially allowing future trajectories to be more tightly constrained. Here we review the timing and onset of human disturbance in and around inland water ecosystems as revealed through sedimentary archives from around the world. Palaeolimnology provides access to a wealth of information reflecting early human activities and their corresponding aquatic ecological shifts. First human impacts on aquatic systems and their watersheds are highly variable in time and space. Landscape disturbance often constitutes the first anthropogenic signal in palaeoli...
The Holocene, 2007
This research uses a comparison of the sediment record of Lake Martiska (NE Estonia) with well-do... more This research uses a comparison of the sediment record of Lake Martiska (NE Estonia) with well-documented historical changes in human impact to identify the factors dominantly affecting the sediment lithological composition, and the accumulation of heavy metals and other microelements into the sediments. To this end, comprehensive lithological-geochemical studies of the upper sediment were undertaken in 1986 and repeated in 2003 and 2005. Oil shale mining and processing heavily impacted the area via atmospheric pollution and groundwater extraction. As a result of the fly-ash deposition clear marker horizons of chemical compounds were formed. Historical water-level fluctuations are clearly reflected in the lithological composition and grain-size variations of the studied sediment cores. During regression and transgression phases displacement of the erosion-transport-accumulation limits caused redistribution of previously accumulated sediments and their return into the biogeochemical ...
Quaternary International, 2012
We applied a complex of methods (spectrophotometry, HPLC, sediment oxygen demand) for the study o... more We applied a complex of methods (spectrophotometry, HPLC, sediment oxygen demand) for the study of fossil pigments in lake sediment. The methods were tested on well-monitored lakes of different trophic status. It was found that the variations in pigment concentrations in the surface sediments of the studied lakes were mainly determined by their degradation before final burial. In the oligotrophic lakes of high Secchi transparency the concentration of fossil carotenoids and chlorophyll derivatives was the lowest and it increased when the photooxidation conditions deteriorated (decreasing transparency, higher trophicity). The individual pigments identified by HPLC analysis were in good correspondence with monitoring data.
Lakes' response to the chances in water chemistry were studied with the aim of acquiring new ... more Lakes' response to the chances in water chemistry were studied with the aim of acquiring new knowledge about protection of the anthropogenically influenced lakes. To evaluate the impact of oil shale mine water on the lake ecosystem status we compared macrophyte compositions of pre-industrial period to nowadays. For a more detailed picture of changes, we used also paleolimnological approach and in sediment cores from two lakes, we analysed sedimentary pigments. Kurtna Lake District is located in the northeastern Estonia, mostly in the territory of the Kurtna Landscape Conservation Area. Kurtna is the lake-richest region in Estonia: there are around 40 lakes per 30 sq. km, from which 18 belongs to the Natura 2000 network of the EU. Same time the Kurtna region is an environmental conflict area. In the beginning of the 1950s, the rapid expansion of oil shale mining and related industry started in the vicinity of Kurtna, raising the need for technological water. For this, the channel...
Lake sediments are sensitive archives of environmental histories. The information derived from se... more Lake sediments are sensitive archives of environmental histories. The information derived from sediment can be helpful for management of aquatic ecosystems affected by anthropogenic impact. However, the analysis of the sediment indicators is often limited by the lack of supportive evidence that would validate the interpretation. This study investigates past changes in three small lakes for which historical monitoring records are available. Short sediment sequences, spanning over 150 years, were investigated using multiple analyses-bulk geochemical composition, fossil pigments and Cladocera remains. The sediment indicators were used to interpret major trends in the degradation of lake ecosystems that occurred during the 20 th century, including changes in lake productivity, algal bloom dynamics, erosion from catchment and pollution. The sediment data were discussed in the context of the historical and lake monitoring evidence. The integration of multiple sources of information confirmed links to the anthropogenic disturbances, primarily on the catchment level i.e. influence of drainage, town development, inflow of mining waters and pollution. The examples show how the sediment indicators provide unique insights about the causes and temporal dynamics of lake ecosystem changes which are relevant for environmental management decisions.
Journal of Soils and Sediments, 2014
Purpose The feasibility of applying the method of single-scan fluorescence emission spectra of hu... more Purpose The feasibility of applying the method of single-scan fluorescence emission spectra of humic substances (HSs) without chemical pretreatments of sediment pore-water samples was tested to ascertain the past productivity and sources of organic matter of lakes. Materials and methods Sediment samples were collected from ten Estonian lakes (located between 57°36′ and 59°25′N and 22°12′ and 26°59′E) covering all levels of the trophic scale. The height (fluorescence intensity), location (fluorescence maximum) and shape (fluorescence index, the ratio of intensities at the emission wavelengths 450 and 500 nm) of the fluorescence emission spectrum at an excitation of 340 nm were under consideration. Results and discussion Pore-water humic substances (pwHSs) from sediments of eutrophic lakes had generally a high fluorescence intensity and fluorescence index and their fluorescence maximum was located at shorter wavelengths. Characteristic features of pwHSs from oligotrophic lakes were low fluorescence intensity, emission of maximum fluorescence at shorter wavelengths and high fluorescence index values. Pore-water humic substances from sediments of dystrophic lakes were characterized by a low fluorescence intensity and fluorescence index and their spectral peak was shifted to longer wavelengths. The study also demonstrated that a shift in the peak location of pwHSs fluorescence was accompanied with a change in the C/N ratios of sedimentary organic matter, and the alteration in the fluorescence index of pw HSs was synchronous with the changes in their molecular weight. Conclusions The obtained results suggest that fluorescence spectroscopy of pwHSs without using chemical pretreatments has a great potential in the reconstruction of past lake conditions.
Journal of Paleolimnology, 2005
The main aim of this study was to reconstruct the history of water level fluctuations of a small ... more The main aim of this study was to reconstruct the history of water level fluctuations of a small dimictic lake during the Holocene based on the lithological and geochemical composition of sediments. We studied lithological and geochemical parameters in sediment cores extracted along a transect through Lake Juusa in southeastern Estonia. Analysis revealed that LOI 550 and CaCO 3 content in the accumulated sediment are dependent on water depth. At depths greater than 3 m, the relationship between organic carbon and CaCO 3 is inverse, whereas no relationship exists at shallower depths. Lake-level changes are well depicted on the grain-size distribution profiles and macrofossil composition. An increase in the >315 lm fraction appeared during the initial phases of water level fluctuations, followed by an increase in the 100-315 lm fraction. The >36 lm fraction dominated the silt fraction. Higher OC/N ratios in shallow water sediments reflect the dominance of macrophytes vegetation.
Estonian Journal of Ecology, 2011
In order to assess the geochemical and stable isotopic response of recent sediments to the changi... more In order to assess the geochemical and stable isotopic response of recent sediments to the changing anthropogenic influence on Lake Nõmmejärv, bulk geochemistry determined by XRF spectroscopy and carbon and oxygen stable isotopes in carbonates (δ 13 C carb and δ 18 O carb ) were analysed. A time scale was defined by the 210 Pb dating method. The most significant change in sediment composition was a steep transition from organic to mineral rich sediment at the beginning of the 1970s. Our data confirm that this shift was caused by an abrupt influx of allochthonous mineral matter (Si, Al, K, Rb, Ti, Zr) derived from mine waters that started to be drained from an oil shale mine into the lake through an artificial channel. Since then, the minerogenic sedimentation remains high but after the initial peak, the proportion of siliciclastic matter decreases in favour of CaCO 3 accumulation. During the last 40 years the carbonate content increased from 7% to 40%. Geochemical evidence supports the assumption that the key mechanism in the formation of carbonates was biologically mediated authigenic CaCO 3 precipitation. In addition, decrease in sediment organic matter due to high minerogenic sedimentation forms more favourable conditions for the preservation of the accumulated CaCO 3 . The shift in the δ 13 C carb values during the 1970s and 1980s indicates potential links between CaCO 3 precipitation and the increase in lake productivity.
Holocene, 2007
This research uses a comparison of the sediment record of Lake Martiska (NE Estonia) with well-do... more This research uses a comparison of the sediment record of Lake Martiska (NE Estonia) with well-documented historical changes in human impact to identify the factors dominantly affecting the sediment lithological composition, and the accumulation of heavy metals and other microelements into the sediments. To this end, comprehensive lithological-geochemical studies of the upper sediment were undertaken in 1986 and repeated in 2003 and 2005. Oil shale mining and processing heavily impacted the area via atmospheric pollution and groundwater extraction. As a result of the fly-ash deposition clear marker horizons of chemical compounds were formed. Historical water-level fluctuations are clearly reflected in the lithological composition and grain-size variations of the studied sediment cores. During regression and transgression phases displacement of the erosion Átransport Áaccumulation limits caused redistribution of previously accumulated sediments and their return into the biogeochemical matter cycling of the lake. The 210 Pb chronology of the sediment records is in contradiction with the historical records of fly-ash emissions, suggesting that changes in 210 Pb flux and focusing of sediments caused by lake-level change have invalidated the dating models.
The Anthropocene Review, 2017
Lake sediments constitute natural archives of past environmental changes. Historically, research ... more Lake sediments constitute natural archives of past environmental changes. Historically, research has focused mainly on generating regional climate records, but records of human impacts caused by land use and exploitation of freshwater resources are now attracting scientific and management interests. Long-term environmental records are useful to establish ecosystem reference conditions, enabling comparisons with current environments and potentially allowing future trajectories to be more tightly constrained. Here we review the timing and onset of human disturbance in and around inland water ecosystems as revealed through sedimentary archives from around the world. Palaeolimnology provides access to a wealth of information reflecting early human activities and their corresponding aquatic ecological shifts. First human impacts on aquatic systems and their watersheds are highly variable in time and space. Landscape disturbance often constitutes the first anthropogenic signal in palaeoli...
The Holocene, 2007
This research uses a comparison of the sediment record of Lake Martiska (NE Estonia) with well-do... more This research uses a comparison of the sediment record of Lake Martiska (NE Estonia) with well-documented historical changes in human impact to identify the factors dominantly affecting the sediment lithological composition, and the accumulation of heavy metals and other microelements into the sediments. To this end, comprehensive lithological-geochemical studies of the upper sediment were undertaken in 1986 and repeated in 2003 and 2005. Oil shale mining and processing heavily impacted the area via atmospheric pollution and groundwater extraction. As a result of the fly-ash deposition clear marker horizons of chemical compounds were formed. Historical water-level fluctuations are clearly reflected in the lithological composition and grain-size variations of the studied sediment cores. During regression and transgression phases displacement of the erosion-transport-accumulation limits caused redistribution of previously accumulated sediments and their return into the biogeochemical ...
Quaternary International, 2012
We applied a complex of methods (spectrophotometry, HPLC, sediment oxygen demand) for the study o... more We applied a complex of methods (spectrophotometry, HPLC, sediment oxygen demand) for the study of fossil pigments in lake sediment. The methods were tested on well-monitored lakes of different trophic status. It was found that the variations in pigment concentrations in the surface sediments of the studied lakes were mainly determined by their degradation before final burial. In the oligotrophic lakes of high Secchi transparency the concentration of fossil carotenoids and chlorophyll derivatives was the lowest and it increased when the photooxidation conditions deteriorated (decreasing transparency, higher trophicity). The individual pigments identified by HPLC analysis were in good correspondence with monitoring data.
Lakes' response to the chances in water chemistry were studied with the aim of acquiring new ... more Lakes' response to the chances in water chemistry were studied with the aim of acquiring new knowledge about protection of the anthropogenically influenced lakes. To evaluate the impact of oil shale mine water on the lake ecosystem status we compared macrophyte compositions of pre-industrial period to nowadays. For a more detailed picture of changes, we used also paleolimnological approach and in sediment cores from two lakes, we analysed sedimentary pigments. Kurtna Lake District is located in the northeastern Estonia, mostly in the territory of the Kurtna Landscape Conservation Area. Kurtna is the lake-richest region in Estonia: there are around 40 lakes per 30 sq. km, from which 18 belongs to the Natura 2000 network of the EU. Same time the Kurtna region is an environmental conflict area. In the beginning of the 1950s, the rapid expansion of oil shale mining and related industry started in the vicinity of Kurtna, raising the need for technological water. For this, the channel...
Lake sediments are sensitive archives of environmental histories. The information derived from se... more Lake sediments are sensitive archives of environmental histories. The information derived from sediment can be helpful for management of aquatic ecosystems affected by anthropogenic impact. However, the analysis of the sediment indicators is often limited by the lack of supportive evidence that would validate the interpretation. This study investigates past changes in three small lakes for which historical monitoring records are available. Short sediment sequences, spanning over 150 years, were investigated using multiple analyses-bulk geochemical composition, fossil pigments and Cladocera remains. The sediment indicators were used to interpret major trends in the degradation of lake ecosystems that occurred during the 20 th century, including changes in lake productivity, algal bloom dynamics, erosion from catchment and pollution. The sediment data were discussed in the context of the historical and lake monitoring evidence. The integration of multiple sources of information confirmed links to the anthropogenic disturbances, primarily on the catchment level i.e. influence of drainage, town development, inflow of mining waters and pollution. The examples show how the sediment indicators provide unique insights about the causes and temporal dynamics of lake ecosystem changes which are relevant for environmental management decisions.
Journal of Soils and Sediments, 2014
Purpose The feasibility of applying the method of single-scan fluorescence emission spectra of hu... more Purpose The feasibility of applying the method of single-scan fluorescence emission spectra of humic substances (HSs) without chemical pretreatments of sediment pore-water samples was tested to ascertain the past productivity and sources of organic matter of lakes. Materials and methods Sediment samples were collected from ten Estonian lakes (located between 57°36′ and 59°25′N and 22°12′ and 26°59′E) covering all levels of the trophic scale. The height (fluorescence intensity), location (fluorescence maximum) and shape (fluorescence index, the ratio of intensities at the emission wavelengths 450 and 500 nm) of the fluorescence emission spectrum at an excitation of 340 nm were under consideration. Results and discussion Pore-water humic substances (pwHSs) from sediments of eutrophic lakes had generally a high fluorescence intensity and fluorescence index and their fluorescence maximum was located at shorter wavelengths. Characteristic features of pwHSs from oligotrophic lakes were low fluorescence intensity, emission of maximum fluorescence at shorter wavelengths and high fluorescence index values. Pore-water humic substances from sediments of dystrophic lakes were characterized by a low fluorescence intensity and fluorescence index and their spectral peak was shifted to longer wavelengths. The study also demonstrated that a shift in the peak location of pwHSs fluorescence was accompanied with a change in the C/N ratios of sedimentary organic matter, and the alteration in the fluorescence index of pw HSs was synchronous with the changes in their molecular weight. Conclusions The obtained results suggest that fluorescence spectroscopy of pwHSs without using chemical pretreatments has a great potential in the reconstruction of past lake conditions.
Journal of Paleolimnology, 2005
The main aim of this study was to reconstruct the history of water level fluctuations of a small ... more The main aim of this study was to reconstruct the history of water level fluctuations of a small dimictic lake during the Holocene based on the lithological and geochemical composition of sediments. We studied lithological and geochemical parameters in sediment cores extracted along a transect through Lake Juusa in southeastern Estonia. Analysis revealed that LOI 550 and CaCO 3 content in the accumulated sediment are dependent on water depth. At depths greater than 3 m, the relationship between organic carbon and CaCO 3 is inverse, whereas no relationship exists at shallower depths. Lake-level changes are well depicted on the grain-size distribution profiles and macrofossil composition. An increase in the >315 lm fraction appeared during the initial phases of water level fluctuations, followed by an increase in the 100-315 lm fraction. The >36 lm fraction dominated the silt fraction. Higher OC/N ratios in shallow water sediments reflect the dominance of macrophytes vegetation.
Estonian Journal of Ecology, 2011
In order to assess the geochemical and stable isotopic response of recent sediments to the changi... more In order to assess the geochemical and stable isotopic response of recent sediments to the changing anthropogenic influence on Lake Nõmmejärv, bulk geochemistry determined by XRF spectroscopy and carbon and oxygen stable isotopes in carbonates (δ 13 C carb and δ 18 O carb ) were analysed. A time scale was defined by the 210 Pb dating method. The most significant change in sediment composition was a steep transition from organic to mineral rich sediment at the beginning of the 1970s. Our data confirm that this shift was caused by an abrupt influx of allochthonous mineral matter (Si, Al, K, Rb, Ti, Zr) derived from mine waters that started to be drained from an oil shale mine into the lake through an artificial channel. Since then, the minerogenic sedimentation remains high but after the initial peak, the proportion of siliciclastic matter decreases in favour of CaCO 3 accumulation. During the last 40 years the carbonate content increased from 7% to 40%. Geochemical evidence supports the assumption that the key mechanism in the formation of carbonates was biologically mediated authigenic CaCO 3 precipitation. In addition, decrease in sediment organic matter due to high minerogenic sedimentation forms more favourable conditions for the preservation of the accumulated CaCO 3 . The shift in the δ 13 C carb values during the 1970s and 1980s indicates potential links between CaCO 3 precipitation and the increase in lake productivity.
Holocene, 2007
This research uses a comparison of the sediment record of Lake Martiska (NE Estonia) with well-do... more This research uses a comparison of the sediment record of Lake Martiska (NE Estonia) with well-documented historical changes in human impact to identify the factors dominantly affecting the sediment lithological composition, and the accumulation of heavy metals and other microelements into the sediments. To this end, comprehensive lithological-geochemical studies of the upper sediment were undertaken in 1986 and repeated in 2003 and 2005. Oil shale mining and processing heavily impacted the area via atmospheric pollution and groundwater extraction. As a result of the fly-ash deposition clear marker horizons of chemical compounds were formed. Historical water-level fluctuations are clearly reflected in the lithological composition and grain-size variations of the studied sediment cores. During regression and transgression phases displacement of the erosion Átransport Áaccumulation limits caused redistribution of previously accumulated sediments and their return into the biogeochemical matter cycling of the lake. The 210 Pb chronology of the sediment records is in contradiction with the historical records of fly-ash emissions, suggesting that changes in 210 Pb flux and focusing of sediments caused by lake-level change have invalidated the dating models.