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Author:Wahlström, Stella
Title:Fosforfrigörelse ur åkerjord som följd av mikrobiologisk järn- och sulfatreduktion
Phosphorus release from agricultural soil due to microbial iron and sulphate reduction
Publication type:Master's thesis
Publication year:2014
Pages:vii + 77 s. + liitt. 11      Language:   swe
Department/School:Kemian tekniikan korkeakoulu
Main subject:Biokemia ja mikrobiologia   (Kem-30)
Supervisor:Nordström, Katrina
Instructor:Ekholm, Petri ; Lehtoranta, Jouni
Electronic version URL: http://urn.fi/URN:NBN:fi:aalto-201405221874
OEVS:
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Location:P1 Ark Aalto  2083   | Archive
Keywords:eutrophication
phosphorus losses
erosion
agriculture
dissimilatory sulphate reduction
dissimilatory iron reduction
anaerobic microbes
bottom sediment
oxygen depletion
sulphate-mediated eutrophication
eutrofiering
övergödning
fosforförluster
erosion
jordbruk
dissimilatorisk sulfatreduktion
dissimilatorisk järnreduktion
anaeroba mikrober
bottensediment
syrebrist
Abstract (eng):In Finland more than half of the anthropogenic phosphorus (P) loading to the Baltic Sea originates from agriculture, and the larger part of the loading is in particulate form.
Until now the potentially bioavailable P has been evaluated by algal assays and chemical extractions.
However, it is unknown how much P is released after the particles have settled on the sea floor, where sulphidic and anaerobic conditions prevail.
Phosphorus release from agricultural soil due to microbiological iron (Fe) and sulphate (SO4) reduction was investigated in two experiments, in which the reducing conditions of bottom sediments were simulated.
The amounts of soil and acetate were varied, the soil serving as a P and Fe source, and acetate as a carbon (C) source for the microbial metabolism.
Sulphate was present among other brackish water ions in the test solution.
The test flasks were inoculated with bottom sediment and incubated for over two years in the dark.
Up to 0.65 mg P per one gram of soil (44% of the total P) was released during the incubation, which exceeded the amount of P extracted by buffered dithionite and NaOH (0.21 mg/g and 0.57 mg/g, respectively).
The results imply that these chemical extractions underestimate the potentially available P.
A regression analysis showed that the P release depended on the amount of both soil and C.
Without C, the release of P was only 25% of the amount that was released with added C.
The decrease of SO4 also depended on C, indicating microbiological SO4 reduction with subsequent hydrogen sulphide formation.
Acetate decreased dissolved Fe, which further indicates precipitation of Fe sulphides.
This precipitation is a probable explanation for the strong P release: Fe in sulphide form cannot bind P.
There appears to be a threshold value for C, over which the P release can be predicted solely by the amount of soil.
This method is suitable for evaluating how much P can be released from eroded soil particles after they end up in bottom sediment of a eutrophic water body, such as the Gulf of Finland.
Abstract (swe):I Finland står jordbruken för över hälften av den antropogena fosforbelastningen till Östersjön, varav största delen är i form av partikulärt fosfor (P).
Hittills har man uppskattat det potentiellt biotillgängliga P med algtester och kemiska extraktioner.
Det är dock oklart hur mycket P som frigörs när partiklarna hamnar på havsbottnen där sulfidhaltiga och anaeroba förhållanden råder.
Fosforfrigörelse ur åkerjord som följd av mikrobiologisk järn- och sulfatreduktion undersöktes i två långvariga experiment, med vilka de reducerande förhållandena i bottensediment simulerades.
Mängden åkerjord och acetat varierades.
Åkerjorden tjänade som P- och Fe-källa och acetatet som kolkälla (C) för mikrobmetabolismen, medan sulfat (SO4) fanns bland andra brackvattenjoner i provlösningen.
Proverna inokulerades med bottensediment och inkuberades i över två år i mörker.
Upp till 0,65 mg P per g jord (44 % av det totala P) frigjordes under inkubationen, vilket överskred mängden P extraherad med buffrad ditionit och NaOH (0,21 mg/g respektive 0,57 mg/g).
Resultaten antyder att dessa kemiska extraktionsmetoder underskattar det potentiellt tillgängliga P.
En regressionsanalys visade att P-frigörelsen berodde på både åkerjord- och C-mängden.
Utan C frigjordes bara 25 % av den mängd P som frigjordes med C tillsats.
Även SO4-minskningen berodde på C, vilket antyder mikrobiologisk SO4-reduktion med resulterande vätesulfidbildning.
Acetat minskade löst järn (Fe), vilket vidare tyder på Fe-sulfidutfällning.
Denna utfällning är en sannolik förklaring till den omfattande P-frigörelsen: Fe kan inte i sulfidform binda P.
Det verkar finnas ett gränsvärde för C över vilket P-frigörelsen kan förutspås enbart på basen av jordmängden.
Denna metod lämpar sig för att bestämma hur mycket P som kan frigöras från eroderade jordpartiklar efter att de sjunkit till bottnen av en eutrofierad vattenmassa, som t ex Finska viken.
ED:2014-06-01
INSSI record number: 49170
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