| | | 11.3 Different N:P loadings, dose-response relationships and points of no return |
Changing N:P loading ratios may affect the biomass yield for a given input. For instance, the maximum autotrophic biomass yield for a given nutrient inputs was obtained at a N:P ratio of approximately 40, without any further increase in biomass yield at higher loading N:P ratios (Figure 5). Nutrients inputs vary between different regions across Europe. For example, there are significant differences between phosphorus and nitrogen loading in the Atlantic and the Mediterranean (Figure 6). These differences in loading N:P ratios result from differences in nutrient sources. In the Atlantic, the main nutrient sources are agriculture, industry and the atmosphere. However, in the Mediterranean they are mainly agriculture and domestic effluents (Duarte and Vidal, unpubl. data). In regional seas and enclosed recipients the variability in loading N:P ratios can even be higher.
Hence, there are indications, derived both from coordinated mesocosm experiments as well as from comparative analyses, that there are (i) major regional differences in nutrient inputs -- both quantity and quality -- and (ii) eutrophication dose-response patterns.
These would, in turn, yield important regional differences in the critical nutrient thresholds that have to be reflected by legislature. There is thus no generic nutrient input -- phytoplankton dose-response relationship in European coastal waters. Adequate information regarding these relationships does only exist for a selected number of regions.
| | | 11.3 Different N:P loadings, dose-response relationships and points of no return |