Together, the isotope and nutrient data suggest that eutrophication by riverine nitrogen is pronounced in the coastal rim of the Baltic Sea, and that coastal sediments appear to be very efficient in removing riverborne nitrogen by denitrification. A nitrogen isotope mass balance model suggests that N loss by sediment denitrification and N input by N fixation can be as high as 855 ktons N yr À1 .

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The eutrophication oflakes in central Europe has been assumed to be at least partly responsible for a widespread die-back offringing Phragmites australLv reeds. To test the 'eutrophication hypothesis' on a broad data basis, lakeshore reed stands at41lakes ofknown trophic status and 10 stands in waste water and sludge treatment plants in Denmark and north Germany (North data subset, n = 26), and south Germany, Switzerland and Austria (South data subset, n = 25) were investigated. A total of 24 culm performance variables in three different shoot classes were analyzed by two-way ANOVA with the geographic origin and the 'relative trophic index' as factors. The geographic origin had a pronounced infiuence on culm architecture. whereas the effect of the trophic level mostly failed to be significant in the ANOVA. The culms from the North reed stands showed a weaker performance throughout than those from the South stands for a given trophic level. However, some of the morphometric traits in the North stands were significant positively correlated with the trophic level but very few significant cases were observed in the South data subset. Three hypotheses are discussed to explain the geographic effect: climatic effects. geochernistry of lake water and sediments, and trophic history of the lakes. It is concluded that lake eutrophication does not infiuence the culm performance negatively and that eutrophication cannot be regarded as a general cause in reed decline.

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