| 1. |
- Adrian, Rita, et al.
(författare)
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Lakes as sentinels of climate change
- 2009
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Ingår i: Limnology and Oceanography. - : Wiley. - 0024-3590 .- 1939-5590. ; 54:6(2), s. 2283-2297
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Tidskriftsartikel (refereegranskat)abstract
- While there is a general sense that lakes can act as sentinels of climate change, their efficacy has not been thoroughly analyzed. We identified the key response variables within a lake that act as indicators of the effects of climate change on both the lake and the catchment. These variables reflect a wide range of physical, chemical, and biological responses to climate. However, the efficacy of the different indicators is affected by regional response to climate change, characteristics of the catchment, and lake mixing regimes. Thus, particular indicators or combinations of indicators are more effective for different lake types and geographic regions. The extraction of climate signals can be further complicated by the influence of other environmental changes, such as eutrophication or acidification, and the equivalent reverse phenomena, in addition to other land-use influences. In many cases, however, confounding factors can be addressed through analytical tools such as detrending or filtering. Lakes are effective sentinels for climate change because they are sensitive to climate, respond rapidly to change, and integrate information about changes in the catchment.
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| 2. |
- Niklasdotter Scherrer, Kim Josefin, et al.
(författare)
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Mechanistic model identifies increasing light availability due to sea ice reductions as cause for increasing macroalgae cover in the Arctic
- 2019
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Ingår i: Limnology and Oceanography. - : Wiley. - 0024-3590 .- 1939-5590. ; 64:1, s. 330-341
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Tidskriftsartikel (refereegranskat)abstract
- In the Arctic, rising seawater temperatures and increasing underwater light caused by reductions in sea ice cover are expected to change the structure of arctic marine communities. Substantial, sometimes sudden, increases in macroalgal productivity and biomass have already been observed in arctic rocky bottom communities. These macroalgal responses have been attributed to increasing temperature and light, but the relative importance of the suggested drivers of change has not yet been assessed. In this study, we used a mechanistic competition model to unravel the effects of temperature and light on benthic community structure and algae dominance, focusing on key algae species: red calcareous algae and macroalgal fronds. We find that light is the primary driver of increases in macroalgal coverage, whereas increased seawater temperature plays a secondary role. Shifts leading to macroalgae dominated communities may be mediated by competitive interactions, and are likely due to three light-related processes: earlier sea ice break-out at high latitudes can result in an exponential increase in the cumulative amount of light that enters the water column during a year; threshold effect in light requirements for algal growth; and light requirements of calcareous algae being substantially lower than those of macroalgae. With continued warming, our modeling results suggest that reduced sea ice coverage and increased light availability will favor dominance of macroalgae, which due to their key ecological role are expected to alter the structure and functioning of arctic rocky bottom ecosystems.
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| 3. |
- Nydahl, Anna, et al.
(författare)
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Colored organic matter increases CO2 in meso-eutrophic lake water through altered light climate and acidity
- 2019
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Ingår i: Limnology and Oceanography. - : Wiley. - 0024-3590 .- 1939-5590. ; 64:2, s. 744-756
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Tidskriftsartikel (refereegranskat)abstract
- Many surface waters across the boreal region are browning due to increased concentrations of colored allochthonous dissolved organic carbon (DOC). Browning may stimulate heterotrophic metabolism, may have a shading effect constraining primary production, and may acidify the water leading to decreased pH with a subsequent shift in the carbonate system. All these effects are expected to result in increased lake water carbon dioxide (CO2) concentrations. We tested here these expectations by assessing the effects of both altered allochthonous DOC input and light conditions through shading on lake water CO2 concentrations. We used two mesocosm experiments with water from the meso‐eutrophic Lake Erken, Sweden, to determine the relative importance of bacterial activities, primary production, and shifts in the carbonate system on CO2 concentrations. We found that DOC addition and shading resulted in a significant increase in partial pressure of CO2 (pCO2) in all mesocosms. Surprisingly, there was no relationship between bacterial activities and pCO2. Instead the experimental reduction of light by DOC and/or shading decreased the photosynthesis to respiration ratio leading to increased pCO2. Another driving force behind the observed pCO2 increase was a significant decrease in pH, caused by a decline in photosynthesis and the input of acidic DOC. Considering that colored allochthonous DOC may increase in a warmer and wetter climate, our results could also apply for whole lake ecosystems and pCO2 may increase in many lakes through a reduction in the rate of photosynthesis and decreased pH.
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| 4. |
- Ricão Canelhas, Monica, et al.
(författare)
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Methane oxidation at the water-ice interface of an ice-covered lake
- 2016
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Ingår i: Limnology and Oceanography. - : WILEY-BLACKWELL. - 0024-3590 .- 1939-5590. ; 61, s. S78-S90
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Tidskriftsartikel (refereegranskat)abstract
- Lakes are important components of the global methane (CH4) cycle. In seasonally ice-covered lakes, CH4 transported by ebullition (bubbling) from anoxic sediments gets trapped at the water-ice interface. If not oxidized by methane-oxidizing bacteria (MOB), this can potentially lead to high episodic CH4 emissions at ice-melt. To understand the fate of CH4 trapped below ice, we measured depth-distributions of CH4 concentrations in the water column near bubbles trapped below ice in Lake Erken. We also performed a 21 d incubation experiment at low temperature (2.3 +/- 0.2 degrees C) to investigate the potential for CH4 oxidation. During most sampling occasions, we found steep CH4 concentration gradients just below the ice with a 13-fold decrease from the surface to a depth of 20 cm. In vitro incubations revealed that CH4 oxidation can occur at low temperatures typical for the water-ice interface. CH4 oxidation was observed as a significant decrease in CH4 concentration, a significant increase in stable isotope C-13 signature, and an increase in MOB during the incubation. Thus, CH4 accumulating in the top 20 cm of the water column, fed by diffusion from CH4 in trapped bubbles, may fuel significant CH4 oxidation. Since northern latitude lakes can be ice-covered for many months of the year and significant amounts of CH4 accumulate below the ice, the extent of CH4 oxidation under these low temperature-conditions is important for understanding the potential CH4 emissions to the atmosphere during ice-melt.
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| 5. |
- Richardson, David C., et al.
(författare)
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Nonlinear responses in interannual variability of lake ice to climate change
- 2024
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Ingår i: Limnology and Oceanography. - : Association for the Sciences of Limnology and Oceanography. - 0024-3590 .- 1939-5590. ; 69:4, s. 789-801
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Tidskriftsartikel (refereegranskat)abstract
- Climate change is contributing to rapid changes in lake ice cover across the Northern Hemisphere, thereby impacting local communities and ecosystems. Using lake ice cover time-series spanning over 87 yr for 43 lakes across the Northern Hemisphere, we found that the interannual variability in ice duration, measured as standard deviation, significantly increased in only half of our studied lakes. We observed that the interannual variability in ice duration peaked when lakes were, on average, covered by ice for about 1 month, while both longer and shorter long-term mean ice cover duration resulted in lower interannual variability in ice duration. These results demonstrate that the ice cover duration can become so short that the interannual variability rapidly declines. The interannual variability in ice duration showed a strong dependency on global temperature anomalies and teleconnections, such as the North Atlantic Oscillation and El Nino-Southern Oscillation. We conclude that many lakes across the Northern Hemisphere will experience a decline in interannual ice cover variability and shift to open water during the winter under a continued global warming trend which will affect lake biological, cultural, and economic processes.
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| 6. |
- Tranvik, Lars J., et al.
(författare)
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Lakes and reservoirs as regulators of carbon cycling and climate
- 2009
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Ingår i: Limnology and Oceanography. - : Wiley. - 0024-3590 .- 1939-5590. ; 54:6:2, s. 2298-2314
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Forskningsöversikt (refereegranskat)abstract
- We explore the role of lakes in carbon cycling and global climate, examine the mechanisms influencing carbon pools and transformations in lakes, and discuss how the metabolism of carbon in the inland waters is likely to change in response to climate. Furthermore, we project changes as global climate change in the abundance and spatial distribution of lakes in the biosphere, and we revise the estimate for the global extent of carbon transformation in inland waters. This synthesis demonstrates that the global annual emissions of carbon dioxide from inland waters to the atmosphere are similar in magnitude to the carbon dioxide uptake by the oceans and that the global burial of organic carbon in inland water sediments exceeds organic carbon sequestration on the ocean floor. The role of inland waters in global carbon cycling and climate forcing may be changed by human activities, including construction of impoundments, which accumulate large amounts of carbon in sediments and emit large amounts of methane to the atmosphere. Methane emissions are also expected from lakes on melting permafrost. The synthesis presented here indicates that (1) inland waters constitute a significant component of the global carbon cycle, (2) their contribution to this cycle has significantly changed as a result of human activities, and (3) they will continue to change in response to future climate change causing decreased as well as increased abundance of lakes as well as increases in the number of aquatic impoundments.
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| 7. |
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| 8. |
- Weyhenmeyer, Gesa A., et al.
(författare)
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Large differences between carbon and nutrient loss rates along the land to ocean aquatic continuum-implications for energy:nutrient ratios at downstream sites
- 2017
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Ingår i: Limnology and Oceanography. - : Wiley. - 0024-3590 .- 1939-5590. ; 62, s. S183-S193
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Tidskriftsartikel (refereegranskat)abstract
- The balance between the availability of energy and nutrients is decisive for the growth and survival of organisms. Here, we evaluated how energy, in this study expressed as total carbon (TC), is lost along the land to ocean aquatic continuum (LOAC) in relation to nutrients, i.e., total phosphorus (TP), total nitrogen (TN), total iron (TFe), and dissolved silica (DSi). For the evaluation, we used data from 4774 lakes, 149 streams, and 52 river mouths from the boreal region. We found that the loss of all chemical variables followed a first order decay function along the LOAC with shortest half-lives for TFe and DSi (410 d and 568 d, respectively). The half-life of TC was more than twice as long as for TFe and DSi, resulting in rapidly increasing TC:TFe and TC:DSi ratios along the LOAC. In contrast, TC:TP and TC:TN ratios decreased along the LOAC. The TC and TFe concentration declines along the LOAC were quantitatively similar to the TC and TFe concentration declines from winter to summer, indicating that similar drivers are responsible for spatial and seasonal TC and TFe losses in inland waters. We conclude that the energy:nutrient ratio rapidly changes along the LOAC with an increasing surplus of energy in relation to TFe and DSi the longer water stays in the landscape. These findings have implications for the growth of aquatic organisms along the LOAC, where organisms are likely to become increasingly iron and silica limited with increasing water retention in the landscape.
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| 9. |
- Weyhenmeyer, Gesa A., et al.
(författare)
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Nitrate-depleted conditions on the increase in shallow northern European lakes
- 2007
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Ingår i: Limnology and Oceanography. - 0024-3590 .- 1939-5590. ; 52:4, s. 1346-1353
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Tidskriftsartikel (refereegranskat)abstract
- We determined relative nitrate-nitrogen (NO3- N) loss rates in 100 north-mid-European lakes from late spring to summer by using the exponential function N-2 5 N-1e(-k)( (t)(2) - (t)(2)), where N-1 and N-2 are NO3- N concentrations at the beginning (t(1)) and the end (t(2)) of the time interval, respectively, and k is the specific NO3- N loss rate. We found that k decreased with increasing lake depth. Adjusting k to the lake depth (k(adj)), we observed that k(adj) was positively related to spring NO3-N concentrations, but this relationship became insignificant at mean lake depths exceeding 12.5 m. A relationship between k(adj) and spring NO3- N concentrations in lakes shallower than 12.5 m implies that changes in spring NO3-N concentrations influence the NO3- N loss rate and thereby summer NO3- N concentrations. Time series from one Estonian, one German, and 14 Swedish lakes shallower than 12.5 m since 1988 revealed that May to August NO3-N concentrations have decreased over time everywhere, and the number of time periods exhibiting a NO3-N depleted condition, i.e., NO3-N levels below 10 mu g L-1, in these lakes has tripled since 1988. We explained the decreasing NO3-N concentrations by a reduction in external nitrogen loading including atmospheric deposition, and by changes in climate. The observed prolongation of NO3- N depleted conditions might be one possible explanation for the increasing occurrence of nitrogen- fixing cyanobacteria in a variety of lake ecosystems.
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| 10. |
- Weyhenmeyer, Gesa A., et al.
(författare)
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Nonlinear response of dissolved organic carbon concentrations in boreal lakes to increasing temperatures
- 2009
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Ingår i: Limnology and Oceanography. - : Wiley. - 0024-3590 .- 1939-5590. ; 54:6, part 2, s. 2513-2519
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Tidskriftsartikel (refereegranskat)abstract
- Recent increases in concentrations of dissolved organic carbon (DOC) in lakes and rivers over large regions have been related to both changes in the climate and in atmospheric deposition chemistry. Using a data set of 1041 boreal lakes along a 13° latitudinal gradient, sampled in 1995, 2000, and 2005, and an additional data set of 90 lakes along a 1000-m altitudinal gradient at 68°N, we show that DOC concentrations increase in a nonlinear way along a latitudinal and altitudinal temperature gradient. The nonlinear relation of DOC to increasing temperatures was consistent over space and time. Out of 14 meteorological, catchment, morphometric, and atmospheric deposition variables tested, the variable best explaining this kind of nonlinear pattern was the number of days when air temperatures exceeded 0°C, i.e., the duration of the main growing and runoff season (DT>0). Using DT>0 as an input variable, we were able to predict the nonlinear temperature response of DOC concentrations, both spatially (R2 = 0.90, p < 0.0001) and temporally (R2 = 0.90, p < 0.0001). DT>0 has an advantage over other variables because it includes the time factor, which is decisive for the duration that biogeochemical processes can take place. We suggest that DOC concentrations in lakes are influenced by climate change and that present temperature increases over Sweden result in an accelerated DOC increase toward warmer geographical regions.
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