| Popis: |
Macrophytes in the littoral zone contribute with a large fraction of the primary production in many lakes. To examine the effect of solar radiation on the degradation of macrophyte detritus. we incubated senescent leaves of Phragmites australis in shallow water in shade, under full solar radiation, and under filters removing either UVB or both UVA and UVB. Several parameters were measured during two months to monitor the composition and quantity of particulate (POM) and dissolved (DOM) organic matter derived from the leaves. Generally, there were no or only small differences between the different radiation treatments, which differed markedly from the shaded microcosms. Hence, more DOM was leached from exposed detritus, corresponding to a higher loss of POM than in the shade. However, the fluorescence of the DOM. an indicator of the concentration of humic matter. was higher in the shade and in microcosms only receiving photosynthetically active radiation (PAR) than in microcosms exposed to UVA or both UVA and UVB, indicating that PAR is not effective in the photolysis of humic matter. This experiment indicates that solar radiation promotes the leaching of DOM from littoral detritus. Not only UV radiation, but also PAR is effective in this process. |
