| 1. |
- Kokfelt, Ulla, et al.
(author)
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Diatoms in peat : dominant producers in a changing environment?
- 2009
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In: Soil Biology and Biochemistry. - : Elsevier BV. - 0038-0717. ; 41:8, s. 1764-1766
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Journal article (peer-reviewed)abstract
- Changes in hydrology and temperature can induce rapid changes in boreal wetland ecosystems. Factors such as hydrosere, permafrost, climate and human interference may disturb the prevailing mire vegetation, whereby a new dominant assemblage can develop. At the transition from one vegetation type to another, the old vegetation may be suppressed, die out or start to decay, and some time may pass until a new mire vegetation is fully established. Here, we demonstrate that diatoms may thrive during such transitions, creating isolated and shallow peat layers with significantly elevated biogenic silica content. Biogenic silica and other nutrients that would otherwise be lost during mineralization in runoff are in this way retained in the ecosystem. Our results imply that silica storage originating from diatoms can be expected to increase in today’s rapidly changing boreal wetlands. The impacts on transport of Si through boreal watersheds are currently unknown.
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| 2. |
- Randsalu Wendrup, Linda, et al.
(author)
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Combining limnology and palaeolimnology to investigate recent regime shifts in a shallow, eutrophic lake
- 2014
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In: Journal of Paleolimnology. - : Springer Science and Business Media LLC. - 0921-2728 .- 1573-0417. ; 51:3, s. 437-448
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Journal article (peer-reviewed)abstract
- In this study, we demonstrate that an integrated approach, combining palaeolimnological records and limnological monitoring data, can increase our understanding of changing ecological patterns and processes in shallow lakes. We focused on recent regime shifts in shallow Lake Krankesjon, southern Sweden, including the collapse of the clear-water state in 1975 and its subsequent recovery in the late 1980s. We used diatom, hydrocarbon and biogenic silica sediment records, in concert with limnological data sets on nutrient concentrations, water clarity, chlorophyll-a and water depth, to investigate the shifts. The shift from clear to turbid conditions was abrupt and occurred over 1 to 2 years, whereas recovery of the clear-water state was more gradual, taking 4-5 years. In 1978, shortly after the first regime shift in water clarity, the diatom community underwent a significant shift. It became less diverse, with decreased abundance of epiphytic and planktonic taxa. Despite rising phosphorus concentrations and lower abundance of submerged macrophytes, Lake Krankesjon has remained in the clear-water state over the past 20 years, although this state seems to be increasingly unstable and susceptible to collapse. The complex reactions of the entire lake ecosystem to major changes in lake-water clarity, as shown by the palaeolimnological variables investigated in this study, emphasize the importance of careful lake and catchment management if a stable, clear-water state is desired.
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| 3. |
- Randsalu Wendrup, Linda, et al.
(author)
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Ecological Regime Shifts in Lake Kälksjön, Sweden, in Response to Abrupt Climate Change Around the 8.2 ka Cooling Event
- 2012
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In: Ecosystems. - : Springer Science and Business Media LLC. - 1432-9840 .- 1435-0629. ; 15:8, s. 1336-1350
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Journal article (peer-reviewed)abstract
- A detailed diatom record from Lake Kälksjön, west-central Sweden, reveals two periods of abrupt ecological change correlative with the 8.2 ka cooling event. Using a combination of abrupt step changes and piece-wise linear regressions, the diatom data were analysed for change points over time, and two sudden and large events that are described as regime shifts were detected. During the first event at c. 8040 cal. yr BP, a doubling in diatom biomass took place over 5-10 years time. This increase in primary productivity can be connected to an erosion event in the catchment that resulted in an abrupt increase in nutrient supply to the lake. The second event was characterised by a substantial shift within the planktonic diatom community from taxa indicative of colder conditions to those indicating warm over 5-10 years at c. 7850 cal. yr BP. This event was superimposed on a successive change from periphytic to planktonic diatom dominance over a 250-year period and a gradual diversification of the periphytic community that spanned c. 150 years. Rapid climate warming following the 8.2 ka event likely caused these changes and both regime shifts are examples of externally driven abrupt ecological change. This study demonstrates that it is possible to detect, quantify and test for regime shifts in paleoecological data, and it highlights the need for high sampling resolution and precise chronological control. High-resolution paleoecological reconstructions of ecological regime shifts in response to climate change can provide useful analogues of future changes in ecosystem structure and functioning.
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| 4. |
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| 5. |
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| 6. |
- Randsalu-Wendrup, Linda, et al.
(author)
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Paleolimnological records of regime shifts in lakes in response to climate change and anthropogenic activities
- 2016
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In: Journal of Paleolimnology. - : Springer Science and Business Media LLC. - 0921-2728 .- 1573-0417. ; 56:1, s. 1-14
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Journal article (peer-reviewed)abstract
- Regime shifts in lake ecosystems can occur in response to both abrupt and continuous climate change, and the imprints they leave in paleolimnological records allow us to investigate and better understand patterns and processes governing ecological changes on geological time scales. This synthesis investigates paleolimnological records that display apparent regime shifts and characterizes the shifts as either smooth, threshold-like or bistable. The main drivers behind the shifts are also explored: direct climate influence on lakes, climate influence mediated through the catchment, lake ontogenetic processes and/or anthropogenic forcing. This framework helps to elucidate the relationship between driver and regime shift dynamics and the type of imprint that the associated regime shifts leaves in sediment records. Our analysis of the limited sites available (22 sites) show that smooth regime shifts are characterized with forcing and response variables acting on similar time scales, whereas regime shifts that demonstrate a threshold like response or a hysteresis response occur on shorter time scales than changes in drivers. The temporal resolution of the record, a common concern in paleo records, limits identification of the timing and rate of the regime shifts. When detected, past regime shifts offer rich opportunities to understand ecosystem responses to climate and other changes and to evaluate the mean state and natural variability of lake ecosystems on time scales of decades to millennia. There are a number of remaining challenges in understanding regime shifts and ecosystem dynamics in a paleolimnological perspective including lack of an appropriate temporal resolution and ecosystem feedback mechanisms. Combining paleoecology with contemporary studies can help clarify the scale of regime shifts and to distinguish patterns in ecosystem changes from natural variability.
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| 7. |
- Randsalu Wendrup, Linda
(author)
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The palaeolimnological record of regime shifts in lakes in response to climate change
- 2013
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Doctoral thesis (other academic/artistic)abstract
- Regime shifts in lake ecosystems can occur in response to both abrupt and continuous climate change, and the imprints they leave in palaeolimnological records allow us to investigate and better understand patterns and processes governing ecological changes on geological time scales. This thesis aims at investigating palaeolimnological records of regime shifts in lakes during the Holocene to explore how lake ecosystems responded to climate changes and anthropogenic activities and to identify thresholds or tipping points that produced regime shifts. The thesis includes case studies of two Swedish lakes and a synthesis of recently published palaeolimnological records displaying regime shifts. In the first case study a detailed diatom record from Lake Kälksjön, west-central Sweden, was investigated for periods of abrupt ecological change associated with the 8.2 ka cooling event. Using change-point analysis we found two regime shifts in the diatom record: one in response to an abrupt erosion event at c. 8040 cal. yr BP, and another caused by climate warming following the 8.2 ka event. The study demonstrates that not only can regime shifts be detected in sediment records, they can also be quantified and statistically tested for, provided that the sampling resolution is high and the chronological control sufficiently precise. The second case study is focused on recent regime shifts between clear-water and turbid states in Lake Krankesjön in southern Sweden. We combined palaeolimnological records and limnological monitoring data, concentrating on the documented collapse of the clear-water state in 1975 and the subsequent recovery in the late 1980s, in order to increase our understanding of changing ecological patterns and processes in shallow lakes. We found that the shift from clear to turbid conditions was abrupt, while the recovery of the clear-water state was more gradual, and the complex and non-linear reactions of the lake to shifting conditions emphasizes the importance of careful lake and catchment management if a stabilization of the clear-water state is desired. In addition to these studies, the theoretical concept of regime shifts is expanded upon in our synthesis of palaeolimnological records with regime shifts, where we characterize the shifts as either smooth, threshold-like or bistable. The examples are also placed within a conceptual model of potential physical processes that produce regime shifts in lakes and the main drivers behind the shifts are identified: direct climate influence on lakes, climate influence mediated through the catchment, lake ontogenetic processes and/or anthropogenic forcing. This framework helps to elucidate the relationship between driver and regime shift dynamics and the type of imprint that the associated regime shifts leave in sediment records. When detected, past regime shifts and palaeolimnological records offer rich opportunities to increase the understanding of ecosystem responses to climate changes and to evaluate the mean state and natural variability of lake ecosystems on timescales of decades to millennia. Palaeolimnological archives provide a perspective on whether the pre-disturbance ”natural” state that may be the target of restoration efforts is actually natural, or if it is an anomaly in lake history, and if this target is at all possible to reach or if it, due to shifting baselines and lake ontogeny, is no longer a realistic restoration endpoint. Furthermore, I argue that linking the timescales of contemporary ecology with palaeoecology/limnology may provide long-term records of lake history and opportunities to further disentangle the role of different forcings on lake ecosystems. An improved understanding of lake ecosystem dynamics and regime shifts in lakes through the cooperation of limnologist/ecologists and palaeolimnologists may better prepare us to face future climate change and to fully understand and perhaps mitigate the effects of global climate change on lake ecosystems.
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| 8. |
- Sparrenbom, Charlotte, et al.
(author)
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Holocene relative sea-level changes in the inner Bredefjord area, southern Greenland
- 2013
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In: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791. ; 69, s. 107-124
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Journal article (peer-reviewed)abstract
- In this paper we present new relative sea-level data from southern Greenland, a key area for understanding the Greenland Ice Sheet (GIS) response to climate change. Within fourteen lakes and marine lagoons from the inner part of Bredefjord (Nordre Sermilik) in southern Greenland, isolations revealed by stratigraphic and palaeoecological analyses are dated and relative sea levels reconstructed. Due to coastal emergence caused by the GIS retreat within the area, the relative sea-level fell rapidly in the early Holocene between at least c. 9600 and c. 7300 cal. yrs BP attaining a rate of 2 cm per year between 9600 and 8000 cal. yrs BP. Spatial variability in relative sea-level changes is show for southern Greenland from a comparison with the Nanortalik and the Qagortoq areas. The regression occurred about 2000 years later in the inner Bredefjord area, compared to the Nanortalik area, and about 1000 years later compared to the Qaqortoq area. This is a consequence of earlier deglaciation in areas located at the outer coast. Between c. 8000 cal. yrs BP and the present day, relative sea level was lower than today. The lowest relative sea level in the Inner Bredefjord area of between -5.4 and -15 m a.h.a.t. (above highest astronomical tide) was reached between 7000 and 1000 cal. yrs BP. The neoglacial readvance together with the collapse of the Laurentide peripheral bulge is probably responsible for the transgression in the Inner Bredefjord area, as has been indicated from the nearby sites Qagortoq and Nanortalik. Our relative sea-level reconstructions showing spatial variability within southern Greenland have implications for Glacial Isostatic Adjustment (GIA) modelling and the understanding of the GIS ice sheet dynamics. The early Holocene regression is consistent with the recession of the southern sector of the GIS from the shelf edge at c. 22 000 cal. yrs BP, reaching inland of the present day outer coast by c. 12 000 cal. yrs BP, and its present margin by c. 10 500 cal. yrs BP. (c) 2013 Elsevier Ltd. All rights reserved.
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