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Many lakes around the world have been exposed to increased nutrient input from anthropogenic sources such as sewage discharge and runoff from fertilised agricultural areas. This has led to eutrophication, manifested as intensified algal blooms, murky waters, oxygen depleted lake bottoms, and alterations of considerable parts of the foodweb. However, many of these lakes have also recovered, due to improved nutrient abatement techniques and to an improved quantitative scientific understanding of eutrophication and its causes. General, predictive models have played a crucial role in the latter development, as they have made it possible to quantitatively assess expected ecosystem changes from various planned actions against eutrophication. The present thesis has been aimed at improving the domain of validity and predictive power of a general, dynamic total phosphorus (TP) model (LakeMab) and to provide the basis for constructing a similar model for total nitrogen (TN). Among the findings in the thesis is that dissolved nitrogen gas is probably always available in excess for nitrogen fixation and nitrogen modelling in eutrophication contexts. Two papers have laid the ground for improved nutrient modelling in calcareous lakes, where sedimentation is particularly pronounced. Static models for predicting concentrations of particulate phosphorus, nitrogen, and organic carbon have been presented that may be incorporated into sedimentation algorithms in dynamic nutrient models. Boundary conditions for various flux algorithms have made it possible to greatly expand the domain of LakeMab for TP. The typical uncertainty of TP concentration values is 17% when predicted with LakeMab, whereas the uncertainty in predictions using older, static models is about twice as high. LakeMab may be very useful for resolving practical issues such as predicting climate-induced eutrophication and drawing up operational guidelines for achieving good water quality as prescribed by, e.g., the European Water Framework Directive.

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<p></p><p>In Sweden, the County Administration board is responsible for improving the water quality in lakes and watercourses according to the European Union Water Framework Directive. In Västmanland county, where river Lillån is situated, the County Administration of Västmanland have the main responsibility for the aquatic environment in that area. The knowledge about the different watercourses in the chatchment of river Lillån is today limited. The aim with this study was to evaluate the ecological quality of River Lillån based on water chemistry analyses and benthic fauna investigations. The aim was also for the benthic fauna to compere different samplingsites and sampling methods with each other in order to see how the species composition changes in the river, and to see the advantages and disadvantages with different sampling tecniques. The methods used for the assessment was presented in a handbook composed by the Swedish Environmental Protection Agency. The results of the study showed that Lillån have good quality concerning acidity and the general ecological status. The benthic fauna investigations indicated high levels of nutrients and thereby resulted in poor status concerning that parameter. The conclusion of the study was that river Lillån does not fulfill the criteria of good status according to the Water Framework Direcive composed by the European Union.</p><p> </p><p><em>Keywords: Water directive, water quality evaulation, benthic fauna, acidification, nutrients, methods for sample-taking.</em></p><p><em></em></p><p><em>Nyckelord: Vattendirektiv, statusbedömning, bottenfauna, försurning, näringsämnen, provtagningsmetoder.</em></p><p> </p>

In Sweden, the County Administration board is responsible for improving the water quality in lakes and watercourses according to the European Union Water Framework Directive. In Västmanland county, where river Lillån is situated, the County Administration of Västmanland have the main responsibility for the aquatic environment in that area. The knowledge about the different watercourses in the chatchment of river Lillån is today limited. The aim with this study was to evaluate the ecological quality of River Lillån based on water chemistry analyses and benthic fauna investigations. The aim was also for the benthic fauna to compere different samplingsites and sampling methods with each other in order to see how the species composition changes in the river, and to see the advantages and disadvantages with different sampling tecniques. The methods used for the assessment was presented in a handbook composed by the Swedish Environmental Protection Agency. The results of the study showed that Lillån have good quality concerning acidity and the general ecological status. The benthic fauna investigations indicated high levels of nutrients and thereby resulted in poor status concerning that parameter. The conclusion of the study was that river Lillån does not fulfill the criteria of good status according to the Water Framework Direcive composed by the European Union.   Keywords: Water directive, water quality evaulation, benthic fauna, acidification, nutrients, methods for sample-taking. Nyckelord: Vattendirektiv, statusbedömning, bottenfauna, försurning, näringsämnen, provtagningsmetoder.

<p>Syftet med denna uppsats är att undersöka huruvida fiskvägar förbi vattenkraftverket vid Finsjö i Emån fungerar eller inte. För att finna svar på den frågan har två olika metoder använts, dels telemetrisändare för att se om fiskar hittar fram till fiskvägarna (attraktionseffektivitet) och dels PIT-tags för att mäta om fiskarna lyckas passera genom fiskvägarna (passageeffektivitet). Undersökningen fann att det var en högre passageeffektivitet, 89 % vid nedre Finsjö och 100 % vid övre Finsjö, i Emån jämfört med andra liknande studier. Attraktionseffektiviteten var 75 % vid nedre Finsjö och 59 % vid övre Finsjö, vilket tyder på att det finns något som stör fisken innan de når fram till fiskvägen, särskilt vid övre Finsjö.</p> / <p>The purpose of this paper is to determine the extent to which trout used fishways to swim past two power plants at Finsjö in River Emån. Two different methods of  collecting data were used, radiotelemetry to determine if fish find the fishways (attraction efficiency) and PIT-tags to measure the number of fish that passed through the fishways (passage efficiency). The study showed that passageefficiency, being 89 % at lower Finsjö and 100 % at upper Finsjö, was high compared to other similar studies. Attraction efficiency was 75 % at lower Finsjö and 59 % at upper Finsjö, which indicates that the fish have difficulty finding the fishway entrances, particularly at upper Finsjö.</p>

Syftet med denna uppsats är att undersöka huruvida fiskvägar förbi vattenkraftverket vid Finsjö i Emån fungerar eller inte. För att finna svar på den frågan har två olika metoder använts, dels telemetrisändare för att se om fiskar hittar fram till fiskvägarna (attraktionseffektivitet) och dels PIT-tags för att mäta om fiskarna lyckas passera genom fiskvägarna (passageeffektivitet). Undersökningen fann att det var en högre passageeffektivitet, 89 % vid nedre Finsjö och 100 % vid övre Finsjö, i Emån jämfört med andra liknande studier. Attraktionseffektiviteten var 75 % vid nedre Finsjö och 59 % vid övre Finsjö, vilket tyder på att det finns något som stör fisken innan de når fram till fiskvägen, särskilt vid övre Finsjö. / The purpose of this paper is to determine the extent to which trout used fishways to swim past two power plants at Finsjö in River Emån. Two different methods of  collecting data were used, radiotelemetry to determine if fish find the fishways (attraction efficiency) and PIT-tags to measure the number of fish that passed through the fishways (passage efficiency). The study showed that passageefficiency, being 89 % at lower Finsjö and 100 % at upper Finsjö, was high compared to other similar studies. Attraction efficiency was 75 % at lower Finsjö and 59 % at upper Finsjö, which indicates that the fish have difficulty finding the fishway entrances, particularly at upper Finsjö.

Viruses has a relatively recently been discovered in high abundances in aquatic systems. Their possible importance has therefore been largely overlooked. In aquatic food webs there should be large differences in carbon and nutrient fluxes depending on whether the main cause of bacterial mortality is viral infection or grazing, where lysis following viral infection should result in a release of organic carbon and nutrients from the lysed bacteria and hence not reach higher trophic levels. Recent research on aquatic viruses has mainly focused on marine environments and the number of studies on freshwater viral ecology is limited. Hence, there is a need for more studies on the importance and functioning of viruses in freshwater systems. The aims of this thesis were to explore the functioning and diversity of viruses that infects bacteria (phages) in freshwater systems. To effectively address this I conducted two experiments and three field studies in 23 lakes in different parts of Sweden. The results show that viral infection and subsequent lysis of the host cell can partly explain the formation of non-nucleoid-containing bacteria and further that viruses can respond to increases in phosphorus concentrations without any net increase in bacterial abundance. Generally, a larger part of bacterial production in lakes were grazed by flagellates than lysed by viruses, but a larger fraction of the total bacterial mortality can be attributed to viruses in hypolimnion compared to in epilimnion. Further, the largest impact of phages on bacterial production may be in humic lakes, which have a relatively high frequency of visibly infected bacterial cells, but low flagellate abundance. Community composition of bacteria and viruses were only weakly coupled in the studied systems. The most important factors for predicting viral community composition were temperature and concentrations of dissolved organic carbon, total phosphorus and soluble reactive phosphorus. The viral community composition changed over the season and temperate phages could be detected by incubations with mitomycin C showing that a large fraction of the viruses detected appeared to be temperate phages. The most important environmental factor co-varying with viral community composition was again concentrations of total phosphorus. To summarize, bacteriophages, as a bacterial mortality factor, are important in freshwater microbial food webs and phosphorus supply has a potential central function in the regulation of the importance of bacteriophages and additionally for viral diversity.

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