Sammendrag
This thesis is a part of a larger project studying chemical status at river mouths and estuaries of six major rivers that flow into the Trondheim fjord. The thesis focuses on the estuary of the three big rivers in Sør-Trøndelag: Orkla, Gaula and Nidelva. Deep sediment cores have been taken from the fjords by the river mouths and these have been analyzed using inductively coupled plasma – mass spectroscopy (ICP-MS). By studying the sediment profiles for selected elements there has been an attempt to uncover historical events of both natural and anthropogenic source. By normalizing elements with aluminum it has been possible to differentiate between natural variations in concentrations and anthropogenic feed of elements. Based on these tools and calculations of the settling velocities there has been made time profiles that revel anthropogenic interferences that has affected the sediments and the water systems. The concentrations in the sediment samples have been compared with the pollutant criterias from KLIF. This study has revealed increased concentrations that probably originate from anthropogenic input of metals in sediment cores outside Orkla and Gaula, including copper, zinc, cadmium, arsenic and lead. The increase of metal concentrations in the upper layers of sediments have been linked to the activity of World War II, mining, industry, development of infrastructure, increased population, modernization of agriculture and possible volcanic eruptions and forest
fires. The sediment core taken outside Nidelva shows no signs of elevated concentrations of metals that come from anthropogenic sources. The exception is arsenic where overlapping potential sources has made it difficult to link the concentrations to any specific sources. Comparisons show that the concentrations in the sediments by the river mouths have larger differences in concentrations in resent time (form 0-12 cm) than further back in time (at 50 cm). Pollution levels in the sediment core’s upper layer by the river mouths shows that the sediment’s upper layer near the river mouth of Orkla is the most polluted one (by copper,
zinc, nickel and cadmium). The sediment’s upper layer by the river mouth of Gaula is second in pollution (by copper and nickel), whereas the sediment’s upper layers taken by the river mouth of Nidelva is least polluted (only by nickel). Nickel contamination in the area seems to have a natural explanation.
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