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dc.contributor.advisorLydersen, Espen
dc.contributor.authorStølen, Maya Therese Runde
dc.date.accessioned2021-08-27T16:12:13Z
dc.date.issued2021
dc.identifierno.usn:wiseflow:2577805:42441538
dc.identifier.urihttps://hdl.handle.net/11250/2771606
dc.descriptionFull text not available
dc.description.abstractA phosphorous mass balance of lake Hålandsvatn was constructed after a weekly monitoring for 19 weeks during the summer of 2019 and was sampled for physicochemical parameters with purpose of estimating alkaline phosphate dissolution in aerobic littoral sediments, and vertical transport of soluble reactive phosphorous across the thermocline from hypolimnion. Lake Hålandsvatn is a temperate, shallow, and eutrophic lake on the south-west coast of Norway which has experienced frequent cyanobacterial blooms for decades, with the microcystein producing cyanobacteria:Planktothrix agardhii. In 2006, external phosphorous inputs have been estimated to 650 kg, and phosphorous loading models suggest 1500 kg of annual phosphorous loading to explain average summer total phosphorous concentrations of 37- 44 ug L-1. Estimates based on a previous study of alkaline phosphate desorption from sediments from lake Hålandsvatn, implies that aerobic soluble reactive phosphorous accounts for 575 kg of the internal loading from lake sediments. Calculations of vertical diffusion and transport estimates 365 kg of soluble reactive phosphorous to have been transported from hypolimnion to epilimnion during the stratified period. The mass balance, assuming that total loading is 1500 kg, does not leave much left of the budget to be accounted for by other important factors which are involved with phosphorous recycling in lake ecosystems. Two weaknesses have been identified: 1) The extraction method used to estimate alkaline phosphate desorption might overestimate release rates, and 2) calculations assume a spatial homogenous distribution and mass, of reactive phosphorous fractions in the lake sediments. Nevertheless, a large proportion of the lake sediments were exposed to high lake water pH reaching close to 10, from early summer until isothermal conditions commenced in early fall. Sediment iron to phosphorus ratio is below 15, which indicates that iron phosphate desorption can occur under certain environmental circumstances. Results suggest that thermocline deepening in lake Hålandsvatn can boost primary production when concentrations of SRP levels are high in hypolimnion. At the end of the summer, thermocline erosion led to an pronounced increase in TP, chlorophyll-a and microcystein. Even if external inputs have been reduced in the last decades, incidents of nutrient rich hypolimnetic water into the trophogenic zone, can sustain large colonies of cyanobacteria, and thereby delay recovery.
dc.description.abstractA phosphorous mass balance of lake Hålandsvatn was constructed after a weekly monitoring for 19 weeks during the summer of 2019 and was sampled for physicochemical parameters with purpose of estimating alkaline phosphate dissolution in aerobic littoral sediments, and vertical transport of soluble reactive phosphorous across the thermocline from hypolimnion. Lake Hålandsvatn is a temperate, shallow, and eutrophic lake on the south-west coast of Norway which has experienced frequent cyanobacterial blooms for decades, with the microcystein producing cyanobacteria:Planktothrix agardhii. In 2006, external phosphorous inputs have been estimated to 650 kg, and phosphorous loading models suggest 1500 kg of annual phosphorous loading to explain average summer total phosphorous concentrations of 37- 44 ug L-1. Estimates based on a previous study of alkaline phosphate desorption from sediments from lake Hålandsvatn, implies that aerobic soluble reactive phosphorous accounts for 575 kg of the internal loading from lake sediments. Calculations of vertical diffusion and transport estimates 365 kg of soluble reactive phosphorous to have been transported from hypolimnion to epilimnion during the stratified period. The mass balance, assuming that total loading is 1500 kg, does not leave much left of the budget to be accounted for by other important factors which are involved with phosphorous recycling in lake ecosystems. Two weaknesses have been identified: 1) The extraction method used to estimate alkaline phosphate desorption might overestimate release rates, and 2) calculations assume a spatial homogenous distribution and mass, of reactive phosphorous fractions in the lake sediments. Nevertheless, a large proportion of the lake sediments were exposed to high lake water pH reaching close to 10, from early summer until isothermal conditions commenced in early fall. Sediment iron to phosphorus ratio is below 15, which indicates that iron phosphate desorption can occur under certain environmental circumstances. Results suggest that thermocline deepening in lake Hålandsvatn can boost primary production when concentrations of SRP levels are high in hypolimnion. At the end of the summer, thermocline erosion led to an pronounced increase in TP, chlorophyll-a and microcystein. Even if external inputs have been reduced in the last decades, incidents of nutrient rich hypolimnetic water into the trophogenic zone, can sustain large colonies of cyanobacteria, and thereby delay recovery.
dc.languageeng
dc.publisherUniversity of South-Eastern Norway
dc.titleA phosphorous mass-balance and implications of sedimentary phosphate release in lake Hålandsvatn
dc.typeMaster thesis


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