| 1. |
- 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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| 2. |
- Logue, Jürg Brendan
(författare)
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Factors influencing the biogeography of bacteria in fresh waters - a metacommunity approach
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- One of ecology’s primary goals is to comprehend biodiversity and its patterns of distribution over space and time. Since microorganisms play a pivotal role in key ecological processes, the diversity of microbial communities may have important implications for the stability and functioning of Earth’s ecosystems. Thus, it is of utmost importance to develop a theoretical foundation but also a conceptual understanding for the mechanisms that generate and maintain microbial diversity. The aim of this thesis is to investigate to what extent local freshwater bacterioplankton diversity, i.e. richness and community composition, is structured by local environmental interactions and/or regional processes. The key objective is to identify ecological linkages between lake bacterioplankton and bacterial communities in connected streams and the surrounding terrestrial landscape, thereby applying a metacommunity approach. To do so, I studied several natural lake bacterioplankton assemblies within different regions of Sweden and assessed both local environmental properties and regional parameters (e.g. dispersal, landscape position). The genetic composition of freshwater bacterioplankton diversity was determined by means of terminal-restriction fragment length polymorphism or 454 pyrosequencing. From the review on the biogeography of bacterioplankton in inland waters it became clear that microbial diversity and its spatial distribution are governed by a complex interplay of both local and regional drivers. In one case, freshwater bacterioplankton communities were structured by local environmental conditions rather than by regional dispersal processes. These local environmental conditions seemed to be equally important in controlling both the total bacterioplankton community and its active fraction. In a study of bacterioplankton communities from five different regions, locally abundant aquatic bacteria were shown to be also regionally widespread, a pattern predicted by neutral theory. Yet, this degree of similarity decreased with increasing environmental heterogeneity. In another study, bacterioplankton richness was controlled mostly by nutrient content, indicating that productivity exerted influence on bacterioplankton richness. However, landscape position and productivity covaried, suggesting that the landscape dictates environmental properties, which then directly structure local bacterioplankton richness. Finally, a review synthesising results from empirical metacommunity approaches and comparing these to theory showed that yet a gap between empirics and theory exists. To conclude, local bacterioplankton diversity appeared to be mainly structured by local environmental properties. However, signatures of neutral processes driving local bacterioplankton community assembly were also recorded.
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| 3. |
- Urrutia-Cordero, Pablo, et al.
(författare)
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Functionally reversible impacts of disturbances on lake food webs linked to spatial and seasonal dependencies
- 2021
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Ingår i: Ecology. - : John Wiley & Sons. - 0012-9658 .- 1939-9170. ; 102:4
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Tidskriftsartikel (refereegranskat)abstract
- Increasing human impact on the environment is causing drastic changes in disturbance regimes and how they prevail over time. Of increasing relevance is to further our understanding on biological responses to pulse disturbances (short duration) and how they interact with other ongoing press disturbances (constantly present). Because the temporal and spatial contexts of single experiments often limit our ability to generalize results across space and time, we conducted a modularized mesocosm experiment replicated in space (five lakes along a latitudinal gradient in Scandinavia) and time (two seasons, spring and summer) to generate general predictions on how the functioning and composition of multitrophic plankton communities (zoo-, phyto- and bacterioplankton) respond to pulse disturbances acting either in isolation or combined with press disturbances. As pulse disturbance, we used short-term changes in fish presence, and as press disturbance, we addressed the ongoing reduction in light availability caused by increased cloudiness and lake browning in many boreal and subarctic lakes. First, our results show that the top-down pulse disturbance had the strongest effects on both functioning and composition of the three trophic levels across sites and seasons, with signs for interactive impacts with the bottom-up press disturbance on phytoplankton communities. Second, community composition responses to disturbances were highly divergent between lakes and seasons: temporal accumulated community turnover of the same trophic level either increased (destabilization) or decreased (stabilization) in response to the disturbances compared to control conditions. Third, we found functional recovery from the pulse disturbances to be frequent at the end of most experiments. In a broader context, these results demonstrate that top-down, pulse disturbances, either alone or with additional constant stress upon primary producers caused by bottom-up disturbances, can induce profound but often functionally reversible changes across multiple trophic levels, which are strongly linked to spatial and temporal context dependencies. Furthermore, the identified dichotomy of disturbance effects on the turnover in community composition demonstrates the potential of disturbances to either stabilize or destabilize biodiversity patterns over time across a wide range of environmental conditions.
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| 4. |
- Urrutia Cordero, Pablo, et al.
(författare)
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Integrating multiple dimensions of ecological stability into a vulnerability framework
- 2022
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Ingår i: Journal of Ecology. - : John Wiley & Sons. - 0022-0477 .- 1365-2745. ; 110:2, s. 374-386
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Tidskriftsartikel (refereegranskat)abstract
- Ecological stability encompasses multiple dimensions of functional and compositional responses to environmental change. Though no single stability dimension used in isolation can fully reflect the overall response to environmental change, a common vulnerability assessment that integrates simultaneously across multiple stability components is highly desirable for ecological risk assessment. We develop both functional and compositional counterparts of a novel, integrative metric of overall ecological vulnerability (OEV). We test the framework with data from a modularized experiment replicated in five lakes over two seasons, examining functional and compositional responses to both pulse and press disturbances across three trophic groups. OEV is measured as the area under the curve integrated over the entire observation period, with the curve delimiting the difference between the disturbance treatment and undisturbed parallel controls, expressed either as the log response ratio of biomass (functional OEV) or community dissimilarity index (compositional OEV). Both, functional and compositional OEV correlated negatively with functional and compositional 'resistance', 'temporal stability' and 'final/extent of recovery' following both pulse and press disturbances, though less so with 'resilience' following a pulse disturbance. We also found a positive correlation between functional and compositional OEV, which reveals the potential to also evaluate the intricate linkage between biodiversity and functional change. Our findings demonstrate that OEV comprises a robust framework to: (a) capture simultaneously multiple functional and compositional stability components, and (b) quantify the functional consequences of biodiversity change. Our results provide the basis for an overarching framework for quantifying the overall vulnerability of ecosystems to environmental change, opening new possibilities for ecological risk assessment and management. Synthesis. Ecological stability comprises multiple dimensions that together encapsulate how ecosystems respond to environmental change. Considering these multiple aspects of stability simultaneously often poses a problem in environmental assessments, which frequently require overarching indicators of risk or vulnerability. While an analysis of multiple dimensions allows for deeper exploration of mechanisms, here we develop and test a new univariate indicator that integrates stability aspects under a broad range of disturbance regimes. Using a modularized experiment in Swedish lakes, we show that this integrative measure captures multiple stability dimensions reflecting compositional and functional vulnerability and their relationships between them.
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| 5. |
- Urrutia-Cordero, P., et al.
(författare)
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SITES AquaNet: An open infrastructure for mesocosm experiments with high frequency sensor monitoring across lakes
- 2021
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Ingår i: Limnology and Oceanography-Methods. - : Wiley. - 1541-5856. ; 19:6, s. 385-400
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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.
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