ABSTRACT
The role of periphyton in primary production was studied in DCA-treated and untreated outdoor microcosms by measuring the assimilation rate of both the periphyton and the phytoplankton ( 14 C-HCO 3 − https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9780203755488/3d2ac8e1-4b0d-4b6d-bebb-2f5a06487770/content/eq4.tif"/> uptake). Glass slides were used as substrates for the periphyton. Nine microcosms of 5.5 m3 volume were filled with artificial fresh water and incubated with organisms. The microcosms were macrophyte-free and sediment-free. After a pre-treatment phase of 90 days, three ponds were used as untreated controls, whereas 5, 20 and 80 µg DCA/L were added to two ponds each. Using this experimental setup, two experiments were conducted. In the first, the glass slides were exposed during the whole time, including the pre-treatment phase, so that the periphyton could establish before the DCA was added. In the second experiment the glass slides were exposed just after the DCA application. The results show that the periphyton generally contributed more than 50% to the total primary production. Only in the treatment with 80 µg DCA/L was the contribution of periphyton less than 50%. With increasing DCA-concentration, the periphyton density and its production rate decreased significantly. This indicates an important role of periphyton in outdoor microcosms, especially in relation to energy and material flow and the possible causes of secondary effects.
