Adsorption of dissolved organic matter in aquatic ecosystems : Effects on composition and reactivity

• Inland waters receive organic matter from terrestrial ecosystems and in situ production. In transit from land to the ocean, dissolved organic carbon (DOC) may be mineralised to inorganic forms (CO2 and CH4) by microbial degradation and photodegradation. It may also transition from dissolved into particulate phase, and be transferred to the sediment and buried. One way in which this can happen is by adsorption of dissolved organic matter (DOM) to mineral particles. This process is rarely studied in inland waters, since suspended particles are often in short supply. However, there are scenarios under which high particle concentrations occur, and in those cases, adsorption may have a substantial effect on DOM composition and reactivity. The overall aim of this thesis was to investigate the potential for DOM adsorption to inorganic particles and the resulting effect on DOM composition, as well as its biological reactivity. Three studies within this thesis focus on different types of surfaces waters in the boreal landscape of Sweden, and one study focuses on coastal moorland streams in the United Kingdom. Adsorption experiments were conducted under controlled laboratory conditions using batch experiments. DOM quality was studied based on bulk optical properties, and composition was examined by high resolution mass spectrometry. Adsorption experiments using a commercially available reference clay (containing substantial amounts of aluminium and iron oxides) as the adsorbent show a widespread potential for DOM in inland water to adsorb to mineral particles. The extent of DOM adsorption in the experiments was regulated by two factors: 1) DOM composition, since compounds with a terrestrial signature were selectively adsorbed, and 2) water chemistry, as adsorption was impaired by pH>7 and higher concentrations of base cations. These general patterns were observed across surface waters with contrasting DOC concentrations, DOM composition and water chemistry parameters, and across spatial and temporal scales. In contrast, adsorption to suspended sediment derived from a glacial stream resulted in the removal of ‘protein-like’ DOM that is produced in situ, rather than terrestrially derived DOM. Hence, the mineralogy of particles may determine which DOM fraction is adsorbed. Experiments examining microbial degradation indicated that the effect of adsorption on the bioavailability of the remaining DOM depends on which DOM fraction is removed by the different adsorbents. This thesis shows that adsorption to mineral particles in aquatic ecosystems is a highly relevant biogeochemical process that has the potential to alter DOM composition and thereby affect its biological reactivity. 

Nyckelord

dissolved organic matter

DOM

carbon

aquatic

adsorption

mineral particles

Biology with specialization in Limnology

Biologi med inriktning mot limnologi

Publikations- och innehållstyp

vet (ämneskategori)

dok (ämneskategori)