Chapter 1: introductionIn this thesis an account is given of a research project dealing with the chemical speciation and bioavailability of copper in Lake Tjeukemeer, a lake in the north of the Netherlands. The reason for the initiation of this project was a lack of knowledge about the speciation of copper and the influence of copper on the behaviour of algae. This influence may be important, because copper is an essential element for algae, but becomes toxic when it is present at too high concentrations. From a literature search it was concluded that free copper can be assumed to control bioavailability for algae. Therefore, it was decided to focus attention on free copper. Currently, no techniques are available that can measure the concentration of free copper directly at the concentration levels typically found in Lake Tjeukemeer. However, some techniques may give useful information, providing that the results are carefully interpreted. As a consequence of the low concentrations of copper, present in natural waters, determinations of copper concentrations are very prone to interferences due to contamination.Chapter 2: copper concentration in Lake Tjeukemeer and external influencesLake Tjeukemeer is a shallow, alkaline and eutrophic lake. It is part of the Frisian "boezem". The hydrology of the lake is man- made: in winter water from the surrounding polders is pumped into the lake and dominates the water composition, while in summer water originating from Lake IJsselmeer is let in. The total "dissolved" (i.e. after filtration through a 0.2 μm pore size filter) copper concentration in Lake Tjeukemeer is typically around 30 nM. Although no evidence could be obtained, it is likely that the copper concentration in the lake is not increased by letting in water from Lake IJsselmeer. However, water originating from the polders probably does increase the copper concentration in Lake Tjeukemeer. It is shown that surface run-off was more likely to cause this elevation than leaching, though during laboratory experiments ...