| 91. |
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| 92. |
- Moss, Brian D., et al.
(författare)
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Climate change and the future of freshwater biodiversity in Europe : a primer for policy-makers
- 2009
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Ingår i: Freshwater Reviews. - : Freshwater Biological Association. - 1755-084X. ; 2:2, s. 103-130
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Tidskriftsartikel (refereegranskat)abstract
- Earth's climate is changing, and by the end of the 21st century in Europe, average temperatures are likely to have risen by at least 2 °C, and more likely 4 °C with associated effects on patterns of precipitation and the frequency of extreme weather events. Attention among policy-makers is divided about how to minimise the change, how to mitigate its effects, how to maintain the natural resources on which societies depend and how to adapt human societies to the changes. Natural systems are still seen, through a long tradition of conservation management that is largely species-based, as amenable to adaptive management, and biodiversity, mostly perceived as the richness of plant and vertebrate communities, often forms a focus for planning. We argue that prediction of particular species changes will be possible only in a minority of cases but that prediction of trends in general structure and operation of four generic freshwater ecosystems (erosive rivers, depositional floodplain rivers, shallow lakes and deep lakes) in three broad zones of Europe (Mediterranean, Central and Arctic-Boreal) is practicable. Maintenance and rehabilitation of ecological structures and operations will inevitably and incidentally embrace restoration of appropriate levels of species biodiversity. Using expert judgement, based on an extensive literature, we have outlined, primarily for lay policy makers, the pristine features of these systems, their states under current human impacts, how these states are likely to alter with a warming of 2 °C to 4 °C and what might be done to mitigate this. We have avoided technical terms in the interests of communication, and although we have included full referencing as in academic papers, we have eliminated degrees of detail that could confuse broad policy-making
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| 93. |
- Münzner, Karla, et al.
(författare)
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Carbon dioxide reduction by photosynthesis undetectable even during phytoplankton blooms in two lakes
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Lakes located in the boreal region are generally supersaturated with carbon dioxide (CO2), which emerges from inflowing inorganic carbon from the surrounding watershed and from mineralization of allochthonous organic carbon. While these CO2 sources gained a lot of attention, processes that reduce the amount of CO2 have been less studied. We therefore examined the CO2 reduction capacity during times of phytoplankton blooms. We investigated partial pressure of CO2 (pCO2) at times of blooms dominated by cyanobacteria (lake Erken, Sweden) or dominated by the nuisance alga Gonyostomum semen (lake Erssjön, Sweden) during two years. Our results showed that pCO2 and phytoplankton densities remained unrelated in the two lakes even during blooms. We suggest that physical factors, such as wind-induced water column mixing and import of inorganic carbon via inflowing waters suppressed the phytoplankton signal on pCO2. These results advance our understanding of carbon cycling in lakes and highlight the importance of detailed lake studies for more precise estimates of local, regional and global carbon budgets.
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| 94. |
- Münzner, Karla, 1989-, et al.
(författare)
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Carbon dioxide reduction by photosynthesis undetectable even during phytoplankton blooms in two lakes
- 2023
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Ingår i: Scientific Reports. - : Nature Publishing Group. - 2045-2322. ; 13:1
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Tidskriftsartikel (refereegranskat)abstract
- Lakes located in the boreal region are generally supersaturated with carbon dioxide (CO2), which emerges from inflowing inorganic carbon from the surrounding watershed and from mineralization of allochthonous organic carbon. While these CO2 sources gained a lot of attention, processes that reduce the amount of CO2 have been less studied. We therefore examined the CO2 reduction capacity during times of phytoplankton blooms. We investigated partial pressure of CO2 (pCO(2)) in two lakes at times of blooms dominated by the cyanobacterium Gloeotrichia echinulata (Erken, Sweden) or by the nuisance alga Gonyostomum semen (Erssjon, Sweden) during two years. Our results showed that pCO(2) and phytoplankton densities remained unrelated in the two lakes even during blooms. We suggest that physical factors, such as wind-induced water column mixing and import of inorganic carbon via inflowing waters suppressed the phytoplankton signal on pCO(2). These results advance our understanding of carbon cycling in lakes and highlight the importance of detailed lake studies for more precise estimates of local, regional and global carbon budgets.
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| 95. |
- Münzner, Karla, 1989-
(författare)
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Causes and consequences of Gonyostomum semen blooms
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Aquatic ecosystems provide essential ecosystem services, but are also highly vulnerable to global change. Climate change, eutrophication and browning, for example, collectively drive the increase of harmful algal blooms in freshwaters. While cyanobacterial blooms have been intensively studied, blooms caused by other algal species have received far less attention.The aim of my thesis was to increase our understanding of the causes and consequences of the freshwater raphidophyte Gonyostomum semen (Ehrenberg) Diesing, which forms high biomass blooms in lakes all over the world. I used laboratory experiments, field studies and lake monitoring data to investigate how G. semen growth is affected by environmental factors related to water color, and how G. semen blooms affect carbon cycling in lakes.High iron concentration (>200 µg L-1) was found to be a requirement for G. semen growth, but not for bloom formation. Rather, increase in dissolved organic carbon (DOC) concentration may drive bloom formation, possibly by a combination of providing additional nutrients to lakes as DOC is imported from terrestrial sources, and by reducing light availability for other competing phytoplankton species. Gonyostomum semen can possibly avoid light limitation and form blooms over a wide range of DOC concentration (8 – 20 mg L-1) due to its diel vertical migration and special pigment composition, although there likely exists a DOC threshold at which also G. semen growth becomes light limited.By fixing CO2 through photosynthesis, G. semen did considerably reduce the partial pressure of CO2 (pCO2) in the studied lakes. Furthermore, the relationship between pCO2 and G. semen became stronger with decreasing DOC concentration, suggesting that reduction in pCO2 caused by G. semen is highest in moderately colored lakes (8 – 12 mg DOC L-1). This resulted in temporary reduction in CO2 emission to the atmosphere during summer, though it is unlikely that it changes annual carbon emissions. Organic matter (OM) generated by G. semen was transported to the sediments, though this did not appear to affect carbon burial rates. However, G. semen increased the fraction of autochthonous OM that sank to the sediment, which may result in altered CO2 and methane (CH4) production on a short-term basis.In summary, G. semen growth is dependent on sufficient iron concentrations, while bloom formation is likely controlled by DOC. Blooms temporarily affect in-lake carbon dynamics through increased rates of CO2 fixation via photosynthesis, transport of autochthonous OM to the sediment and subsequent changes in CO2 and CH4 production. Thus, G. semen may contribute to changes in ecosystem functioning in lakes experiencing browning.
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| 96. |
- 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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| 97. |
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| 98. |
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| 99. |
- Nydahl, Anna Cecilia
(författare)
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Carbon Dioxide in Inland Waters : Drivers and Mechanisms Across Spatial and Temporal Scales
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Inland waters are an essential component of the global carbon cycle as they are very active sites for carbon transformation processes. Much of this carbon is transformed into the greenhouse gas carbon dioxide (CO2) and emitted into the atmosphere. The biogeochemical and hydrological mechanisms driving CO2 concentrations in inland waters are manifold. Although some of them have been studied in detail, there are still knowledge gaps regarding the relative importance of the different CO2-driving mechanisms, both on a spatial and a temporal scale. The main aim of this thesis was to fill some of the knowledge gaps by studying long- and short-term effects of enhanced dissolved organic carbon (DOC) concentrations on surface water partial pressure of CO2 (pCO2) as well as to investigate both internal (i.e., within the water body) and external (i.e., catchment) drivers of pCO2 in inland waters. Based on analyses of long-term data from more than 300 boreal lakes and streams and on results from two mesocosm experiments as well as a detailed catchment study, one of the main results of the thesis was that DOC concentrations were, on a temporal scale, generally uncoupled to pCO2. Indeed, additions of allochthonous DOC to lake water could result in increased pCO2 in waters but not as originally expected by stimulation of bacterial activity but instead by light driven suppression of primary production, at least in mesotrophic waters. Changes in the carbonate system was also found to be a main driver for surface water pCO2. Finally, also external processes such as groundwater inputs contributed substantially to variations of surface water pCO2. In a detailed study on carbon in groundwater, pCO2 in groundwater was found to decrease with soil depth and correlated negatively with pH, which increased with soil depth. Conclusively, this thesis show that pCO2 does not follow the trends of increased DOC in boreal surface waters but instead correlates with changes in primary production and shifts in the carbonate system. Additionally, the dominating mechanisms driving pCO2 clearly differ between lakes and streams. Consequently, simulations of future CO2 dynamics and emissions from inland waters cannot rely on DOC concentrations as a pCO2 predictor, but rather need to incorporate several pCO2 driving mechanisms, and consider the difference between lakes and streams.
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| 100. |
- Nydahl, Anna C., et al.
(författare)
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Groundwater carbon within a boreal catchment : spatiotemporal variability of a hidden aquatic carbon pool
- 2020
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Ingår i: Journal of Geophysical Research - Biogeosciences. - 2169-8953 .- 2169-8961. ; 125:1
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Tidskriftsartikel (refereegranskat)abstract
- Groundwater is an essential resource providing water for societies and sustaining surface waters. Although groundwater at intermediate depth could be highly influential at regulating lake and river surface water chemistry, studies quantifying organic and inorganic carbon (C) species in intermediate depth groundwater are still rare. Here, we quantified dissolved and gaseous C species in the groundwater of a boreal catchment at 3- to 20-m depth. We found that the partial pressure of carbon dioxide (pCO(2)), the stable carbon isotopic composition of dissolved inorganic carbon (delta C-13-DIC), and pH showed a dependency with depth. Along the depth profile, a negative relationship was observed between pCO(2) and delta C-13-DIC and between pCO(2) and pH. We attribute the negative pCO(2)-pH relationship along the depth gradient to increased silicate weathering and decreased soil respiration. Silicate weathering consumes carbon dioxide (CO2) and release base cations, leading to increased pH and decreased pCO(2). We observed a positive relationship between delta C-13-DIC and depth, potentially due to diffusion-related fractionation in addition to isotopic discrimination during soil respiration. Soil CO2 may diffuse downward, resulting in a fractionation of the delta C-13-DIC. Additionally, the dissolved organic carbon at greater depth may be recalcitrant consisting of old degraded material with a greater fraction of the heavier C isotope. Our study provides increased knowledge about the C biogeochemistry of groundwater at intermediate depth, which is important since these waters likely contribute to the widespread CO2 oversaturation in boreal surface waters.
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