| 1. |
- Chakrawal, Arjun, 1992-
(författare)
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Novel approaches in modeling of soil carbon : Upscaling theories and energetics
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Soils contain more carbon (C) than terrestrial (above ground) and atmospheric carbon combined. Mismanagement of soil C could lead to increased greenhouse gas emissions, whereas practices leading to increased C storage would help mitigate climate change while improving soil fertility and ecological functions. At the center of these complex feedbacks, soil microorganisms play a pivotal role in the cycling of C and nutrients, and thus in soil-climate interactions. However, this role is not fully understood; therefore, developing new methods for studying their dynamics is essential for an understanding of bio-physicochemical processes leading to mineralization or stabilization of soil organic matter (SOM).Current soil C cycling models lack a robust upscaling approach that links SOM decomposition from process (μm) to observation scale (cm to km). Moreover, these models often neglect energy fluxes from microbial metabolism, which may provide additional constraints in model parameterization and alternative observable quantities such as heat dissipation rate to study decomposition processes. In this doctoral work, I investigated two aspects of microbial processes and their consequences for SOM dynamics: 1) use of energetics to constrain SOM dynamics by explicitly accounting for thermodynamics of microbial growth, and 2) spatial constraints at microscale resulting from the non-uniform distribution of microorganisms and substrates.In the first part of the thesis, I developed a general mass and energy balance framework for the uptake of added substrates and native SOM. This framework provided the theoretical underpinnings for understanding variations in the calorespirometric ratios—the ratio of rates of heat dissipation to CO2 production—a useful metric used as a proxy for microbial carbon-use efficiency (CUE). Moreover, in a follow-up work, I extended this mass-energy framework to describe dynamic (time-varying) conditions, which was used to interpret rates of heat and CO2 evolution from different soils amended with glucose. The dynamic mass-energy framework was also used as a tool for data-model integration and estimation of microbial functional traits, such as their CUE and maximum substrate uptake rates. In the second part of the thesis, I linked the micro and macroscale dynamics of decomposition using scale transition theory. The findings of this study were further validated from laboratory experiments, in which spatial heterogeneity in the added substrate was manipulated.Results from the first part show that the calorespirometric ratios can be used to identify active metabolic pathways and to estimate CUE. Further, the heat dissipation rate can be used as a reliable complement or alternative to mass fluxes such as respiration rates for estimating microbial traits and constraining model parameters. In the second part, I show that the co-location of microorganisms and substrates increased, and separation decreased the microbial activity measured as heat dissipation from the incubation experiment. These results were in line with the expectation from the scale transition theory. In summary, this work provides novel approaches for studying soil C cycling and explicitly highlights a way forward to address two fundamental issues in microbial decomposition—the role of spatial heterogeneities and of energetic constraints on microbial metabolisms.
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| 2. |
- Livsey, John, 1983-
(författare)
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Sustainable agriculture : From global challenges to local land management
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Despite the success of agriculture management practices in increasing the availability of food needed to meet the requirements of the expanding global population, there are increasing demands placed on the resources on which the sector depends. Opportunities for the development of agricultural systems are constrained by increasing competition, from other sectors, for shared resources. In tackling this constraint, agricultural management solutions are often narrowly focused on problems related to single resources. But this single focus may lead to unintended trade-offs. To make sound management decisions, there is a need to better understand trade-offs which may occur from resource use efficiency solutions implemented in the agricultural sector. With a particular focus on soil and water resources, the aim of this thesis was to investigate trade-offs that occur, when meeting demands placed on agriculture systems, if management solutions are narrowly focused. Broadly, we hypothesize that approaches to land management that take a more holistic view of agricultural systems being part of an ecosystem mosaic should be adopted to ensure sustainability. A global assessment of potential land requirements shows that national level production of sufficiently nutritious food may be constrained by land availability, such that allocation of land to nutritious crop production might come at the cost of lost land for other crops or uses. This constraint will be the most prevalent in African states. In further studies, we focused on the management of water resources, which are becoming particularly limiting for crops that have high water demands, such as rice. Through a meta-analysis of paired plot experiments, which assessed the effect of water saving irrigation in rice production, and soil sampling within An Giang, a major rice producing province of Vietnam, we examined the effect of water management practices on soil properties. The meta-analysis finds that significant reductions in soil organic carbon, and potentially organic matter bound nutrients, have been observed when water efficient practices replace continual flood irrigation. This suggests that, although yield reductions may not be seen in the short term, water saving irrigation may, over time, lead to reductions in soil fertility and yields. Within An Giang province, there are concerns regarding the loss of flood-borne, nutrient rich, sediments in fields where the annual flood waters have been completely regulated. However, we find that this complete regulation does not result in reduced soil nutrient properties when compared to areas where floods are only partially regulated. The effect of different land management practices on soil properties were further explored within the Kilombero Valley, Tanzania. Comparing farming practices along a gradient of intensity, we found contrasting effects of irrigation and fertilization, with irrigation increasing soil organic carbon and fertilization reducing soil organic carbon. Overall, the results of this thesis highlight the importance of looking beyond meeting short term needs, which can have negative long term consequences. The success of land management practices implemented now do not, necessarily, equate to their continued success in the future. As demands placed on agriculture are going to increase, the long term trade-offs which may occur from present practices must be at the forefront of agricultural management.
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| 3. |
- Mulokozi, Deogratias, 1986-
(författare)
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Integrated Agriculture and Aquaculture Systems (IAA) for Enhanced Food Production and Income Diversification in Tanzania
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Aquaculture production in Tanzania has increased in recent years, responding to an increased demand for fish, partly because of an increasing population and declining catches of wild fish. However, the current aquaculture production is still low, dominated by small scale farming systems, that are struggling with a number of challenges such as lack of improved fish breeds, feeds, technical skills and low adoption rates.This thesis aims to assess the status of fish pond farming with a focus on integrated agriculture and aquaculture (IAA) systems in Tanzania, and to provide guidance on how these systems could be further developed to help local farmers to diversify their food production and income generation.Methodologies included field observations, interviews, structured questionnaires, field experiments and laboratory analyses. Two field surveys in six districts and seven regions of Tanzania provided insights on the current status and the contribution of small-scale pond farming and IAA to household income and food production. Differences between IAA and non-IAA fish farming practices, and their influence on farm productivity and profitability were assessed. Also, opportunities, constraints and farmers’ future plans for fish farming were explored. Two field experiments were conducted on selected IAA systems identified during the surveys. One assessed the effect of including amaranth (Amaranthus hybridus) waste in locally produced fish feed on the yield of Nile tilapia (Oreochromis niloticus). Another investigated how the combination of different vegetables (A. hybridus and Brassica rapa pekinensis) and stocking densities of O. niloticus affected the water use efficiency, need for synthetic fertilizers and overall farm productivity and profitability.The results show that small scale fish farming contributed with 13% of the farmers’ income. 38% of the fish was used for consumption and the remaining part was sold, contributing to both food security and livelihood diversification. Integration of tilapia and vegetables was the most common type of IAA system applied. Local feed ingredients contained medium to high content of crude protein, with high fat content in some animal by-products. The fish yield from the IAA ponds was 60% higher compared to non-IAA ponds because of a more frequent use of on-farm resources and better management. The net income from IAA ponds was 175% higher compared to non-IAA ponds, due to reduced costs and higher yields. Major constraints included water problems, lack of technical skills and good quality fish seeds and feeds. Overall, fish farmers had a positive attitude towards fish farming and the majority were willing to continue with fish farming, with IAA farmers being more positive than non-IAA farmers. The use of amaranth wastes as a fish feed ingredient in a tilapia-amaranth integrated system did not affect the fish growth and yield, but rather improved the feed conversion ratio. The multiple use of water in integrated tilapia-vegetable systems increased the water use efficiency and reduced the need for synthetic fertilizers. Although water from high fish stocking densities increased the vegetable yield, the overall farm productivity in the IAA system was negatively affected because of low fish growth and survival rates. Since agriculture is already popular and fish farming is expanding, promotion of IAA systems could provide an entry point for an increased adoption of aquaculture among rural farmers.
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| 4. |
- Oostdijk, Maartje, 1988-
(författare)
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Fisheries Management under Individual Transferable Quota : Outcomes for Ecology and Equity
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The management of marine resources pose a difficult commons problem as monitoring behavior is difficult and benefit flows from the resources are uncertain. Implementing individual transferable quota (ITQ) is a management regime in which quasi-property rights are assigned for an often mobile and uncertain environmental resource, fish or marine invertebrates. This thesis addresses sustainability impacts of ITQ’s as a fisheries management tool. The findings demonstrate that fisheries management regimes in which fisheries opportunities are allocated as quota and / or are allocated individually experience reduced overfishing compared to controls that do not have these attributes (Paper I), however the analysis found less support for transferability and no support for longer duration being associated to any change in the probability of overfishing. In addition, a longitudinal study showed that with an adaptive design ecological and economic goals could be balanced in an important mixed fishery in Iceland (Paper II), and based on such findings suggested that several policy changes could be implemented to modify the ecological risk of catch-quota balancing allowances. Additional longitudinal analyses allowed to conclude that rapid consolidation in an important small-boat fishing sector in Iceland, which may have had negative implications for local fishing communities (Paper III), and that on average since the introduction of ITQ’s total amount of quota traded stayed below around 60% for the main commercial species in the Icelandic ITQ system. Moreover, the results of Paper IV also show that in case of a credible announcement of quota revocation in the future there would be scope for policy reform. Finally, research is beginning to emerge that shows that marine species are unequally affected by climate change. In a final chapter the analyses show that under different scenarios of global change a re-shaping of the Icelandic foodweb is likely (Paper V). The re-shaping of the foodweb will be to the benefit of some resource users and to the loss of others. In general, the findings from all the analyses together demonstrate that there could be benefits to individual quota implementation for fisheries sustainability and that some of the hypothesized trade-offs could potentially be balanced, the thesis highlights ways forward in investigating the common pool problems in fisheries management.
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| 5. |
- Rocha, Eva, 1985-
(författare)
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Trees and the environment : Possibilities and challenges in tree-ring research across spatial and temporal scales based on case studies in Sweden.
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The need to understand and quantify the magnitude and frequency of past and current environmental changes increased the demand for high-resolution proxy data across spatial and temporal scales. Due to their long lifespan and global distribution, trees provide a unique and continuous record of environmental variability. More specifically, trees can be used as proxies of environmental conditions since their physical and chemical characteristics reflect the conditions in which they have been growing.Focused on case studies from Sweden, this thesis presents a sample of applications where different tree-ring parameters were combined and compared with meteorological records, historical documents and soil profiles to provide information on natural and human-induced changes in the environment. Tree-ring width (TRW) measurements from living trees and subfossil wood from Jämtland, west-central Sweden, were combined to develop a two-millennia-long chronology from Norway spruce, a species that has been traditionally overlooked in dendroclimatic assessments in the region. This record enabled delivery of new perspectives on past regional climate variability and represents an important achievement for inter-and intraregional proxy analyses.A unique maximum latewood density (MXD) chronology was developed from trees growing in drought-prone environments in the Stockholm Archipelago and used to reconstruct past precipitation variability for east-central Sweden. The results showed that MXD provides a stronger climate–growth relationship than TRW and allows a broader target seasonal average (May - July) to be reconstructed.The resolution provided by ring width and density measurements is insufficient to understand growth responses to environmental stress at intra-annual scales. A pilot study using stem radial increment data retrieved from several dendrometers placed in the Stockholm area provided important insights into daily and seasonal growth dynamics in response to site-specific conditions. The main results show that short-term events, such as droughts, can significantly impact trees’ climate–growth relationship and their vegetative period.Annually resolved time-series of wood elemental composition were used to investigate environmental contamination at a glassworks site in southern Sweden. The dendrochemical signals showed large variability both between and within the species in analysis, suggesting a strong control of the soil properties and species-specific uptake on trees’ elemental composition.The findings presented in this thesis show that tree rings can be a highly suitable proxy to understand past and ongoing environmental changes and the link between ecosystems, climate and human activities. Overall, regionally developed networks of tree-ring data elucidated processes behind large-scale climate dynamics and provided new insights on past regional climate variability. In addition, locally-focused studies revealed fine-grained variations and the challenges of understanding the numerous physiological interactions between individual trees and the surrounding environment.
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| 6. |
- Vigouroux, Guillaume, 1991-
(författare)
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Managing coastal eutrophication : Land-sea and hydroclimatic linkages with focus on the Baltic coastal system
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Eutrophication endangers coastal ecosystems all over the world and is most often associated with an increase in anthropogenic nutrient loads to coastal waters, which fuel the growth of algae and create a variety of environmental problems. This is also the case for the Baltic Sea where coastal waters may be affected by various land, coast-sea, and hydroclimatic drivers and feedbacks, over different scales, including the eutrophic open sea. This thesis aims at improving our understanding of how these drivers affect coastal eutrophication and its management opportunities across the various coupled scales of the Baltic land-coast-sea system. To achieve this aim, the interactions between land-catchment, coastal, and open sea processes, and their influences on coastal eutrophication have been investigated through water quality modelling with applications to specific Baltic coastal waters. Hydroclimatic influences on the propagation of change-impacts through the land-coast-sea continuum to coastal eutrophication have also been investigated via the water quality modelling and additional analysis of actual water quality trends over the last 30 years along the Swedish coast. Moreover, coastal eutrophication research on the Baltic Sea system has been investigated through scientific literature analysis with focus on how the reported research has accounted for and linked components in the land-coast-sea system, and the aim to identify possible research gaps.Results show that impacts of water quality improvements in the open sea propagate to a large share of the coastal waters, especially for phosphorus and phytoplankton, while impacts of reducing nutrient loads from land are more localised and more pronounced for nitrogen than for phosphorus. Therefore, reducing coastal nitrogen, phosphorus and phytoplankton concentrations requires both regional measures for open sea improvements and local land-catchment measures for reduction of nutrient loads to the specific coast. Moreover, data analysis shows that trends in coastal Summer chlorophyll a (Chl-a) are well correlated with those in open sea Summer Chl-a and in riverine nitrogen loads. Regarding hydroclimatic drivers, warmer and wetter conditions are found to complicate remediation of coastal eutrophication in comparison to drier and colder conditions. In addition, trends in coastal Summer Chl-a are well correlated with those in sea-ice conditions. These results highlight the various land-based, coastal, open sea, and hydroclimatic drivers and conditions that mix, interact in and influence the coastal waters. The various driver, management, and ecosystem components involved are overall included in Baltic coastal eutrophication research. However, specific coastal management measures, and feedbacks between drivers and impacts of coastal eutrophication are under-investigated, and the social and ecological components of the whole land-coast-sea system are not well-connected in the research.Furthermore, long-lived legacy sources on land, as well as at sea, have not been much accounted for in coastal eutrophication research so far. This calls for further research on recovery time scales and specific remediation measures that can be effective against such sources, like mussel farming and wetlands. Finally, coastal eutrophication management needs to account for the influences on local coastal conditions from a melting pot of multi-scale drivers and biogeochemical as well as ecological impacts and feedbacks.
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