Waterborne sediment and pollutant transport into lakes and accumulation in lake sediments

Sammanfattning: The general objective of this thesis is to contribute to the knowledge of the transport of sediments and pollutants from catchments to downstream water recipient systems and their accumulation in these systems, such as lakes and lake sediments. One part of the thesis studies the importance of drainage reach morphology and water flow for the phosphorous (P) transport and retention in the reaches, and the main controlling processes of the P retention in the reach sediments. The second part of the thesis investigates and describes the environmental history of sediment, P and metal transport into and accumulation in the sediments of bay Karlskärsviken, a typical near-shore zone in Lake Mälaren, west of Stockholm, Sweden. The thesis generally shows that the investigated P and metal loads (except for lead) into the near-shore zones of Lake Mälaren have increased over the last 30-40 years and, in spite of environmental regulation, not yet started to decrease. The thesis further shows that the P retention rate in drainage reaches depends on the reach depth and water flow, where shallow reaches retain P faster than deeper ones. A decrease of reach depth and/or water flow, e.g., by allowing ditches to meander and/or become overgrown with vegetation, may therefore decrease the P and possibly also other nutrient and pollutant loading into the recipient waters.