Studies have concluded that streams emit CO2, which indicates that natural sources of Greenhouse Gases can contribute to climate changefeedback. Why this is of interest is to be able to make reliable climate models. These studies are however debated, since there are differentmethods to measure CO2 evasion from streams which conclude that different hydrological and chemical factors are affecting the gas exchange themost. It is based on an upside-down-placed chamber in the streams, containing a sensor which is able to directly measure the partial pressure ofCO2 (pCO2) in streams. An advantage with this method is that it is built on cheap equipment and therefore can be afforded to cover a bigcatchment with differing hydrological factors. The aim for the thesis is to evaluate the usefulness of this new method by running several statisticalanalyses on the collected data and also by comparing the trend from the statistical results to other methods statistical trends of pCO2. What can beconcluded by this study is that discharge affects the pCO2 in streams and it often appears with a negative correlation. Also, diurnal patterns ofpCO2 seem to appear, with a peak before lunch and minimum levels in the afternoon, which could indicate that pCO2 are dependent onphotosynthesis/respiration and/or temperature. These conclusions are of interest to understand how C acts in freshwater and respond to the climatechange. The study has to be extended with investigation of how more factors affect pCO2 and also some improvement for the method, before itcan be fully used. / Forskning har visat att små skogsbäckar släpper ut CO2 och på så sätt bidrar de till naturliga utsläpp av växthusgaser ochklimatförändringar. Studiernas resultat är dock debatterade då de till att börja med används olika metoder för att dra dessa slutsatser,vilka pekar på både olika kvantiter av CO2 utsläpp och också på olika påverkan från hydrologiska och kemiska faktorer. På grund avdetta har en alldeles ny metod utvecklats. Den grundar sig på en uppochnervänd kammare placerad i vatten som med hjälp av eninbyggd sensor fångar upp och mäter partialtrycket CO2 (pCO2) i vattnet. En fördel är att den är byggd av enkelt material til l lågt pris,vilket gör att metoden kan användas på många platser samtidigt, då man har råd med ett stort antal kammare. Målet för avhandlingenär att utvärdera nyttan av denna nya metod genom att köra flera statistiska analyser på de insamlade uppgifterna och även genom attjämföra utvecklingen från statistiska resultaten till andra metoder statistiska trender av pCO2. Studien kan visa att vattenhastighetenpåverkar pCO2 från bäckarna, och korrelationens struktur är betydande på vattennivån i bäcken. Man kan även dra slutsatser om attdet finns en dygnsrytm i hur CO2 släpps ut från bäckar med högsta utsläpp under förmiddagen och lägsta på eftermiddagen. Dettaskulle kunna bero på att CO2 utsläpp beror på fotosyntes/respiration och/eller temperaturskillnader. Dessa slutsatser är väldigtintressanta för att bygga på kunskapen om hur kolemissioner från sötvatten påverkas av klimatförändringarna. Om man utökar studienmed fler möjliga variabler för att studera hur andra miljöfaktorer påverkas pCO2 och modifiera metoden och datainsamlandet något såkan detta vara en metod värd att fortsätta användas.

Biogas is a gaseous composition formed mainly by the methane gas (CH4) and by the carbon dioxide (CO2), generated especially by microbiologic processes in environment with few or no oxygen. This research was carried out on the biogas produced from the treatment of swine dejections in breathing decomposition and accumulated in the interior of biodigestors, in swine culture in the state of Rio Grande do Sul. Within the range of this present work, the same gas is rusted and it turns into CO2 by the burning in flare. Through the literature review and applied questionnaires, possibilities of treatment of swine objections were raised, through comparative flow chart. Through measuring the biogas flow in appropriate equipments and mathematic analyses, several conclusive results were reached. It was tried to evidence not only the various possibilities of biogas use, mainly the generation of electric energy, but also the heating of swine culture in the winter. It was approached the necessary equipments to invest in the first item mentioned, as well as deadlines for these investments return. From another point of view , it was evidenced the biogas nonuse in aid of the swine culture, but the investment in a Mechanism of Clean Development (MCD) to obtain the Credits of Carbon, where it was observed the great difficulties, mainly financial, to a swine breeder implant the same. Several technical and economical possibilities to mitigate the greenhouse effect were analyzed. / Biogás é uma composição gasosa formada principalmente pelo gás metano (CH4) e pelo dióxido de carbono (CO2), gerado especialmente por processos microbiológicos em ambiente com pouco ou nenhum oxigênio. Esta pesquisa foi realizada sobre o biogás produzido a partir do tratamento de dejetos suínos em decomposição anaeróbica e acumulado no interior de biodigestores, em suinocultura do Estado do Rio Grande do Sul. No âmbito do presente trabalho, o mesmo é oxidado e transforma-se em CO2 pela queima em flare. Através da revisão da literatura e questionários aplicados, foram levantadas possibilidades de tratamento dos dejetos suínos, através de fluxogramas comparativos. Através da medição da vazão do biogás em equipamentos apropriados e análise matemática, obteve-se resultados conclusivos. Procurou-se evidenciar as diversas possibilidades de aproveitamento do biogás, principalmente a geração de energia elétrica, mas também o aquecimento da suinocultura no inverno. Abordou-se os equipamentos necessários para investir no primeiro item anteriormente citado, assim como prazos para retorno destes investimentos. De outro ângulo de visão , evidenciou-se o não aproveitamento do biogás em benefício da suinocultura, mas o investimento em um Mecanismo de Desenvolvimento Limpo (MDL) para obter os Créditos de Carbono, onde observou-se as grandes dificuldades, principalmente financeiras, para um suinocultor implantar o mesmo. Diversas possibilidades técnicas e econômicas para mitigar o efeito estufa foram analisadas.