| 1. |
- Münzner, Karla, 1989-
(författare)
-
Causes and consequences of Gonyostomum semen blooms
- 2022
-
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.
|
|
| 2. |
- Patriarca, Claudia, 1986-
(författare)
-
Characterisation of natural dissolved organic matter with liquid chromatography and high resolution mass spectrometry
- 2020
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Dissolved organic matter (DOM) is one of the most heterogeneous and complex mixture on Earth. DOM plays a crucial role in biogeochemical processes on the global scale and it is essential to sustain and regulate the biological processes in aquatic ecosystems. DOM originates from a multitude of biological, physical and chemical transformations, leading to its phenomenal chemical diversity. In order to understand and predict its effect on the global carbon cycle, an intimate characterization at molecular level is necessary. The investigation of the extraordinary complexity of the DOM mixture represents a compelling challenge for analytical chemistry. The focus of this thesis was the development of methods for the characterization of DOM in natural waters. High resolution mass spectrometry (HRMS), was combined with high pressure liquid chromatography (HPLC) and electrospray ionization (ESI), to investigate the chemical diversity of DOM. The first study demonstrated that cutting-edge techniques (such as the Fourier-transform ion cyclotron resonance mass spectrometer - FTICR-MS), are not indispensable to disclose essential information on the DOM molecular composition, in fact the Orbitrap mass analyser is a suitable alternative for the analysis of complex natural mixtures. In the second study, the potential benefits offered by the online coupling of HPLC and HRMS instruments were explored, revealing significant advantages in terms of analysis time, achievable information and versatility of the method. The advantages of online separation were further confirmed in the third study, focused on the characterization of autochthonous labile DOM. Chromatographically resolved profiles emerged from the bulk-DOM, allowing the monitoring of labile autochthonous components in presence of heterotrophic bacteria. Despite the advantages achieved by the application of online separation, a strong limiting factor in DOM characterization is the ESI source, suitable only for the analysis of the DOM fraction susceptible to ionization. In the last study, the extent of the DOM material prone to ionization was estimated, revealing the occurrence of an extensive portion of the material resistant to routinely employed ESI approach. The full characterization of DOM is still an open challenge and the combination of multiple techniques is fundamental to unravel is extreme intricacy.
|
|
| 3. |
- Eiler, Alexander, 1976-
(författare)
-
The Niches of Bacterial Populations in Productive Waters : Examples from Coastal Waters and Four Eutrophic Lakes
- 2006
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Recent research in microbial ecology has focused on how aquatic bacterial communities are assembled. Only a few of these studies follow a “Gleasonian” approach where the roles of single bacterial populations are in focus. In this thesis, novel molecular tools were used to describe the distribution and evolutionary relationships of microbes in productive aquatic environments. Many new phylogenetic groups of bacteria were identified, likely representing bacterial populations restricted to productive freshwaters. I also addressed the dynamics and functional role of individual bacterial populations in eutrophic lakes and brackish environments with a focus on either biogeochemically significant or potentially pathogenic representatives. Flavobacteria blooms were observed, on occasions characterized by high heterotrophic production. In addition to high temporal dynamics microbial community composition and function differed on the spatial scale, as exemplified by free-living and Cyanobacteria-associated habitats. At the community scale, microbial processes, such as biomass production and substrate uptake could be predicted from the presence and absence of individual bacterial populations. I also studied the niches of potentially pathogenic Vibrio populations in various coastal waters. Using a novel culture-independent method, a V. cholerae population was detected along the entire Swedish coastline. Results from an environmental survey and a laboratory mesocosm experiment reveal that phytoplankton-derived dissolved organic matter enhance the growth of V. cholerae and other Vibrio spp. and hence create a largely overlooked niche for these heterotrophic bacteria. This thesis and future work on the role of individual bacterial populations will facilitate predictions of biogeochemical cycles and the distribution of bacteria in the context of global climate change and local eutrophication.
|
|
| 4. |
- Jansen, Joachim, 1989-, et al.
(författare)
-
Global increase in methane production under future warming of lake bottom waters
- 2022
-
Ingår i: Global Change Biology. - : John Wiley & Sons. - 1354-1013 .- 1365-2486. ; 28:18, s. 5427-5440
-
Tidskriftsartikel (refereegranskat)abstract
- Lakes are significant emitters of methane to the atmosphere, and thus are important components of the global methane budget. Methane is typically produced in lake sediments, with the rate of methane production being strongly temperature dependent. Local and regional studies highlight the risk of increasing methane production under future climate change, but a global estimate is not currently available. Here, we project changes in global lake bottom temperatures and sediment methane production rates from 1901 to 2099. By the end of the 21st century, lake bottom temperatures are projected to increase globally, by an average of 0.86-2.60 degrees C under Representative Concentration Pathways (RCPs) 2.6-8.5, with greater warming projected at lower latitudes. This future warming of bottom waters will likely result in an increase in methane production rates of 13%-40% by the end of the century, with many low-latitude lakes experiencing an increase of up to 17 times the historical (1970-1999) global average under RCP 8.5. The projected increase in methane production will likely lead to higher emissions from lakes, although the exact magnitude of the emission increase requires more detailed regional studies.
|
|
| 5. |
- Sobek, Sebastian, 1973-
(författare)
-
Carbon Dioxide Supersaturation in Lakes – Causes, Consequences and Sensitivity to Climate Change
- 2005
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The global carbon cycle is intimately linked with the earth’s climate system. Knowledge about carbon cycling in the biosphere is therefore crucial for predictions of climate change. This thesis investigates the carbon dioxide balance of Swedish boreal lakes, its regulation, significance to the carbon budget of the boreal landscape, and sensitivity to climate change. Swedish boreal lakes were almost exclusively supersaturated in CO2 with respect to the atmosphere, resulting in an emission of CO2 from lakes to the atmosphere. Lake pCO2 was closely related to the concentration of terrigenous dissolved organic carbon (DOC), indicating that the utilization of terrigenous DOC by lake bacteria is a major source of CO2. This conclusion is supported by independent field studies, showing that net plankton respiration accounts for most of the CO2 emitted from Swedish boreal lakes, while photochemical mineralization and sediment respiration were less important. Mineralization of terrigenous DOC and subsequent emission of CO2 from lakes to the atmosphere was a major carbon loss factor in 21 major Swedish boreal catchments, removing 30-80% of the organic carbon exported from terrestrial soils to surface waters. Lake CO2 emission is in the same order of magnitude as organic carbon accumulation in boreal forest soils, and should therefore be included in the carbon budget of the boreal landscape. In a set of nearly 5000 global lakes, DOC concentration was a much more important regulator of lake pCO2 than temperature. Climate change will therefore affect the carbon balance of lakes primarily via alterations in terrestrial DOC export, rather than via changes in temperature per se. Both current observations and models of future climate suggest an increasing export of terrigenous DOC from many Scandinavian catchments. Hence, there probably is a current trend towards higher CO2 emission from Swedish boreal lakes, which is likely to continue in the future.
|
|
| 6. |
- Urrutia-Cordero, P., et al.
(författare)
-
SITES AquaNet: An open infrastructure for mesocosm experiments with high frequency sensor monitoring across lakes
- 2021
-
Ingår i: Limnology and Oceanography-Methods. - : Wiley. - 1541-5856. ; 19:6, s. 385-400
-
Tidskriftsartikel (refereegranskat)abstract
- For aquatic scientists mesocosm experiments are important tools for hypothesis testing as they offer a compromise between experimental control and realism. Here we present a new mesocosm infrastructure-SITES AquaNET-located in five lakes connected to field stations in Sweden that cover a similar to 760 km latitudinal gradient. SITES AquaNet overcomes major hindrances in aquatic experimental research through: (i) openness to the scientific community, (ii) the potential to implement coordinated experiments across sites and time, and (iii) high-frequency measurements (temperature, photosynthetic photon flux density, turbidity and dissolved oxygen, chlorophyll a and phycocyanin concentrations) with an autonomous sensor system. Moreover, the infrastructure provides operational guidance and sensor expertise from technical staff, and connections to a multi-layered monitoring programme ("SITES Water") for each lake. This enables ecological observations from whole lake ecosystems to be compared with experimental studies aiming at disentangling major drivers and mechanisms underlying observed changes. Here we describe the technical properties of the infrastructure along with possibilities for experimental manipulations to tackle pressing issues in aquatic ecology and global change science. As a proof of concept, we also present a first mesocosm experiment across all five field sites with a cross-factorial design to evaluate responses of the sensor measurements to press/bottom-up (constant light reduction) and pulse/top-down (temporary fish predation) disturbances. This demonstrates the suitability of the infrastructure and autonomous sensor system to host modularized experiments and exemplifies the power and advantages of the approach to integrate a network of mecsocosm facilities with manageable costs across large geographic areas.
|
|
