Fordeling av metaller og organisk materiale langs en norsk elv – hav transekt

The distribution of metals in aquatic systems is crucial for bioavailability and toxicity. Metals are transported from catchment to oceans through rivers. During this transport, the properties of metals (e.g., charge, size, and toxicity) are often strongly altered by chemical, physical and biological transformational processes. Specifically, terrestrial organic matter (ter-OM) may be a significant vector for trace metal transport across the land-to-sea continuum. According to the European Commission, integrative comprehension of the fate and effects of contaminants in different compartments of these transitional environments (estuarine sediment, water, biota) is still required to better establish, assess, and monitor the good ecological and chemical status targeted by the Water Framework Directive. Questions remain as to which role salinity and associated increased ter-OM precipitation play along this gradient, i.e., when, how, and why metals and organic material distribute as they do along the river to sea transect. This thesis considers the distribution of 15 different metals (Al, Si, Ca, Cr, Mn, Fe, Ni, Cu, Zn, As, Mo, Ca, Pb, Mg, Na) in surface water along a river-ocean transect situated in southern Norway (Storelva – Sandnesfjorden transect). After collecting water surface samples at 10 different sites along the transect, laboratory analysis of in-situ samples was conducted to assess the quantity and quality of organic material (OM), metal contribution, and size distribution (dissolved versus particulate fraction). Additional UV/VIS spectrophotometric analysis at specific wavelengths was conducted to determine the properties of dissolved organic matter (DOM) (< 0.22 μm). In sum, there was detected a decrease in ter-OM and associated river-borne particle reactive metals (Al, Pb, Fe, Mn and, Si) along the river-ocean transect (i.e., highest values at riverine site, lowest at the marine site). The opposite trend, an increase along the gradient, was observed for ocean-associated metals (Ca, Mg, Na, Mo, As, but also Cr). There was detected a sudden change in element concentration at the mixing zone of fresh and saltwater. However, the location of the mixing zone varied between samplings due to variations in river flow and tidal water. Analysis of OM properties analysis indicated a decrease in color, aromaticity, humic content, and size, indicating a greater portion of terrestrial input of organic matter at the river site compared to the marine site. Coastal zones are discussed as important zones for blue economy, especially in Norway. To achieve sustainable use of coastal resources, it is necessary to obtain knowledge of pollution in these areas. This study provides important new insights regarding the distribution, transformation, and cycling of organic matter and metals, with a special focus on ter-OM and associated metals, along river-ocean transects.Distribusjonen av metaller i akvatiske systemer er avgjørende for biotilgjengelighet og toksisitet. Metaller transporteres fra nedbørsfelt til hav gjennom elver. Under denne transporten endres egenskapene til metaller (f.eks. ladning, størrelse og toksisitet) sterkt ved kjemiske, fysiske og biologiske transformasjonsprosesser. Spesielt kan terrestrisk organisk materiale (ter-OM) være en viktig vektor for spormetalltransport over land-til-sjø-kontinuum. Ifølge EU-kommisjonen er det nødvendig med bedre forståelse av skjebnen og effektene av forurensninger i disse overgangsmiljøene (estuariesediment, vann, biota) for å bedre etablere, vurdere og overvåke den gode økologiske og kjemiske statusen som kreves av EUs vanndirektiv. Det mangler fortsatt kunnskap om hvilken rolle salinitet og ter-OM spiller langs denne gradienten, dvs. når, hvordan og hvorfor metaller og organisk materiale fordeler seg som de gjør langs elv-hav gradienter. Denne oppgaven vurderer fordelingen og konsentrasjonen av 15 forskjellige metaller (Al, Si, Ca, Cr, Mn, Fe, Ni, Cu, Zn, As, Mo, Ca, Pb, Mg, Na) i overflatevann langs en elv - hav transekt i Sør-Norge (Storelva - Sandnesfjorden transekten). Etter å ha samlet prøver fra 10 stasjoner av overflatevann langs transekten ble laboratorieanalyse av in-situ prøver utført for å kvantifisere mengde og kvalitet av organisk materiale (OM), metallbidrag og størrelsesfordeling (oppløst versus partikkelfraksjon). Ytterligere UV/VIS spektrofotometrisk analyse ved spesifikke bølgelengder ble utført for å bestemme egenskaper av løst organisk materiale (DOM) (