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Här visas endast kommande disputationer som är publicerade i DiVA.
Henry H. Hansen
Biologi
Institutionen för miljö- och livsvetenskaper (from 2013)
A Spatial Scale Approach to Fish Habitat Ecology and Impacted Rivers
Doktorsavhandling, sammanläggning
Datum: 2024-04-25
Tid: 10:00
Plats: Fryxellsalen, 1B306, Universitetsgatan 2, Karlstad
Abstrakt
Fish habitat in rivers is under threat from severe anthropogenic impacts. Pollution, dams, water use, hydropeaking, and invasive species are now common in rivers around the world and their combined effects on riverine fish habitat have reduced freshwater fish biodiversity at an unprecedented rate. River managers rely on models to inform management and restoration in order to improve fish habitat. Historically, these models have prioritized individual fish species but managing fish biodiversity requires understanding of resources, risks, and conditions for entire fish communities. These components that make up the foundation of fish habitat have inherent scale dependencies. Thus, a more holistic approach to modeling will need greater attention to spatial scale, ranging from small streams up to entire watersheds. To move beyond current limitations, models must be capable to operate at a variety of spatial scales and address the most pressing issues in rivers. This thesis investigates fish habitat ecology in impacted rivers using a novel spatial scale approach. The approach improves the model development process for fish habitat in rivers. Using the approach, multiple models were developed that address specific impacts on fish communities in rivers around the world.
Workson Siwale
Miljö- och energisystem
Institutionen för ingenjörs- och kemivetenskaper (from 2013)
Doktorsavhandling, sammanläggning
Datum: 2024-05-07
Tid: 08:30
Plats: Rejmersalen, 9C 204, Karlstad University, Karlstad
Abstrakt
Wood pellets have become a preferred solid biomass fuel for heat and power generation due to their standardized nature, known properties, and consistent quality. However, pellets produced from fresh sawdust sometimes undergo self-heating and off-gassing and this poses a challenge for their transportation and storage. The aim of this thesis was to increase the body of knowledge towards understanding the mechanisms underlying the self-heating and off-gassing of wood pellets.
The results from paper I showed that the total amount of extractives in the raw material has little effect on off-gassing. Although pellets produced from Scots pine sawdust with lower extractive contents exhibited reduced concentrations of off-gasses; CO, CO2 and CH4, increasing the extractive content of the sawdust through the addition of additive oils did not result in increased off-gas emissions. The results of pure cellulose pellets with added additive oils showed that off-gassing is influenced by the type of extractives in the raw material (paper II). The highest concentrations of off-gasses were recorded from pure cellulose pellets with added linseed oil due to their high content of unsaturated fatty acids of 73.9% linolenic and 7.6% linoleic.
The results from papers III and IV indicated significant effects of both raw material and drying temperature on off-gassing and self-heating of wood pellets. There was a strong linear correlation between off-gassing and the sapwood content of the raw material, with correlation coefficient (R) values greater than 0.9 at p < 0.001 for all the off-gases (paper III). An increase in sapwood content led to a significant increase in off-gassing of CO2, CO and CH4, and O2 consumption. Storing of sawdust for over six months prior to pellet production, and increasing the drying temperature led to a significant reduction in off-gassing for sapwood pellets. For heartwood pellets, increasing the drying temperature resulted in increased off-gassing while raw material storage had no effect. In the other study (paper IV), the pellets produced from Scots pine mature wood sawdust were more prone to self-heating and off-gassing compared to those produced from juvenile wood sawdust. Steam drying the sawdust at high temperature led to a significant reduction in heat and gas generation for both materials.
The overall results indicated that a biological process, in combination with the chemical oxidation of unsaturated fatty acids lay behind the self-heating and off-gassing of wood pellets.