Syftet med denna uppsats är att undersöka om det finns någon mätbar korrelation mellan kiselalgskomplexet Fragilaria capucinas storlek och halten av fosfor i det vattendrag där de lever. Om ett samband finns kan detta efter ytterligare studier komma att bli användbart inom miljöövervakningen då bland annat vattendragens eutrofieringsgrad ska undersökas. Studien baseras på arkiverade kiselalgspreparat som finns på Institutionen för vatten och miljö (IVM). Arton prover med varierande fosforhalter valdes ut, och tjugo F. capucina räknades i varje prov.

A research of 14 toxic affected study sites in Sweden showed a significant increased proportion of deformed diatoms. The six metal polluted study sites in the region of Dalarna showed a 4, 2% average of deformed Fragilaria (deformed diatoms reference sites, 0, 1%). The results also indicate a significant increased proportions of deformed diatoms in the eight pesticide polluted sites in the south and middle of Sweden, compared to the reference sites, howsoever the toxic content was low. The results indicate that there are no lager differences in neither teratological forms nor variations that segregate metal polluted and pesticide polluted shells. One of the reasons may be that both heavy metals and pesticides can affect the development of the diatom shell..

Benthic diatoms are used in Sweden for monitoring water quality in run-ning water; the method is also frequently used in other countries in Europe. One of the problems of the diatom method is the need for sedimentation of the fresh sample, to be able to decant the over standing water and add alco-hol as a preservations solution. To my knowledge, no results have been published about how long the settling time must be to ensure that the ben-thic diatoms really have settled down to avoid a loss of the diatoms when decanting the over standing water. The aim of my investigation was to improve the Swedish method where the benthic diatoms are used for water quality monitoring. I wanted to find out the appropriate time necessary to wait until all diatoms have settled down before decanting the over standing water. First, fresh benthic diatom samples were taken in the river Fyrisån and the lake Mälaren on different days. After arriving in the laboratory, I waited three different times (30 min, 60 and 180 min) for the diatoms to settle.