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- Bonaglia, Stefano, 1983-
(författare)
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Control factors of the marine nitrogen cycle : The role of meiofauna, macrofauna, oxygen and aggregates
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The ocean is the most extended biome present on our planet. Recent decades have seen a dramatic increase in the number and gravity of threats impacting the ocean, including discharge of pollutants, cultural eutrophication and spread of alien species. It is essential therefore to understand how different impacts may affect the marine realm, its life forms and biogeochemical cycles. The marine nitrogen cycle is of particular importance because nitrogen is the limiting factor in the ocean and a better understanding of its reaction mechanisms and regulation is indispensable. Furthermore, new nitrogen pathways have continuously been described. The scope of this project was to better constrain cause-effect mechanisms of microbially mediated nitrogen pathways, and how these can be affected by biotic and abiotic factors.This thesis demonstrates that meiofauna, the most abundant animal group inhabiting the world’s seafloors, considerably alters nitrogen cycling by enhancing nitrogen loss from the system. In contrast, larger fauna such as the polychaete Marenzelleria spp. enhance nitrogen retention, when they invade eutrophic Baltic Sea sediments. Sediment anoxia, caused by nutrient excess, has negative consequences for ecosystem processes such as nitrogen removal because it stops nitrification, which in turn limits both denitrification and anammox. This was the case of Himmerfjärden and Byfjord, two estuarine systems affected by anthropogenic activities, such as treated sewage discharges. When Byfjord was artificially oxygenated, nitrate reduction mechanisms started just one month after pumping. However, the balance between denitrification and nitrate ammonification did not favor either nitrogen removal or its retention.Anoxia is also present in aggregates of the filamentous cyanobacteria Nodularia spumigena. This thesis shows that even in fully oxic waters, millimetric aggregates can host anaerobic nitrogen processes, with clear implications for the pelagic compartment. While the thesis contributed to our knowledge on marine nitrogen cycling, more data need to be collected and experiments performed in order to understand key processes and regulation mechanisms of element cycles in the ocean. In this way, stakeholders may follow and take decisions in order to limit the continuous flow of human metabolites and impacts on the marine environment.
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| 2. |
- Ekeroth, Nils, 1982-
(författare)
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Benthic fluxes of biogenic elements in the Baltic Sea : Influence of oxygen and macrofauna
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis investigates how benthic fluxes of phosphorus (P), nitrogen (N), and silicon (Si) change upon oxygenation of anoxic soft bottoms in the brackish, eutrophicated Baltic Sea. Direct measurements in situ by benthic landers demonstrated that fluxes of dissolved inorganic P (DIP) from anoxic bottom sediments in the Eastern Gotland Basin are higher than previously thought (Paper I). It is argued that the benthic DIP flux has a much larger influence on the DIP inventory in the Baltic proper than the external sources. Similarly, benthic fluxes of DIP and dissolved inorganic N (DIN) from anoxic sediment in the coastal Kanholmsfjärden Basin, Stockholm archipelago, were sufficiently high to renew the pools of these nutrients below the upper mixed layer in roughly one year (Paper II).A natural inflow of oxygen rich water into the deep, and previously long-term anoxic part of Kanholmsfjärden Basin, increased the P content in the sediment by 65% and lowered DIP and dissolved silica (DSi) concentrations in the pore water. These changes, as well as the large increases in benthic effluxes of these solutes following de-oxygenation of the bottom water, suggest that they are influenced similarly by changing oxygen conditions.Experimental results in papers III and IV show that common benthic macrofauna species in the Baltic Sea can stimulate benthic release of DIN and DSi, as well as dissolved organic and particulate bound nutrients. Thus, if benthic oxygen conditions would improve in the Baltic, initial effects on benthic–pelagic nutrient coupling will change due to animal colonisation of currently azoic soft bottoms.A new box corer was designed (Paper V) which can be used to obtain highly needed virtually undisturbed samples from soft bottom sediments – if lowered slowly and straight into the bottom strata – as demonstrated by in situ videography and turbidimetry. The commonly used USNEL box corer caused severe biasing during sediment collection.
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| 3. |
- Hall, Caroline, 1979-
(författare)
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Empirical Essays on Education and Social Insurance Policies
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis consists of four self-contained essays. Essay 1: This paper evaluates the effects of the introduction of a more comprehensive upper secondary school system in Sweden in the 1990s. The reform reduced the differences between the academic and vocational educational tracks through prolonging and substantially increasing the academic content of all vocational tracks. The effects of this policy change are identified by exploiting a six year pilot scheme, which preceded the actual reform in some municipalities. The results show that the prolongation of the vocational tracks brought about an increased probability of dropping out among low performing students. Though one important motive behind the policy change was to enable all upper secondary school graduates to pursue a university degree, I find no effects on university enrolment or graduation. There are some indications, however, that attending the longer and more academic vocational tracks may have led to increased earnings in the long run. Essay 2: (co-authored with Peter Fredriksson, Elly-Ann Johansson and Per Johansson) We examine whether the impact of pre-school interventions on cognitive skills differs by immigrant background. The analysis is based on Swedish data containing information on childcare attendance, rich family background information, the performance on cognitive tests at age 13, and long-run educational attainment for cohorts born between 1967 and 1982. We find that childcare attendance reduces the gap in language skills between children from immigrant backgrounds relative to native-born children. We find no differential effects on inductive skills, however. Nor does childcare appear to affect the distribution of long-run educational attainment. Essay 3: (co-authored with Laura Hartman) This paper studies a specific type of moral hazard that arises in the interplay between two large public insurance systems in Sweden, namely the sickness insurance (SI) and the unemployment insurance (UI). Moral hazard can arise from the structure of the benefit levels as for some unemployed persons benefits from the SI are higher than benefits from the UI. We use a reform of the SI system that came into force on 1 July 2003 to identify the effect of economic incentives arising from the different benefit levels. The purpose of the reform was to eliminate the difference in benefits between the two insurance systems. Our results from a duration analysis show clearly that the higher the sickness benefits, the higher the probability of reporting sick. Essay 4: Previous research suggests that there are substantial interactions between the unemployment insurance (UI) and the sickness insurance (SI) in Sweden. Moral hazard arises in the interplay between these two social insurance systems, since by reporting sick an unemployed person can postpone the UI expiration date and sometimes also receive considerably higher benefits. This paper examines whether these interactions affect the transition rate from unemployment to employment. To study this question I utilize a reform which greatly reduced the incentives for unemployed persons to transfer to the SI. While there is evidence that this reform substantially lowered the incidence of sick reports among the unemployed, I find no evidence suggesting that the reduced sick report rate in turn affected the transition rate to employment.
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