The decline of nature values in shallow standing waters in Flanders is often correlated with an oversupply of nutrients as nitrogen (N) and phosphorus (P). The exchange of nutrients between water and sediment is very complex and the uptake by submerged plants via roots and shoots depends on the growth form. Under oligotrophic and mesotrophic conditions the competition for nutrients is high and species rich vegetations are often found, combining many growth forms and vulnerable and rare species. These vegetations often contain very valuable fauna-elements. To propose protection, management, and nature development objectives for these water types a better understanding of the complex relationships between the nutrient content in the different compartments (water-sediment-plant) and the development and species richness of the vegetation is necessary. Especially a better view on the nutrient limitation determining valuable vegetation types is required. The role of the sediments in the nutrient limitation of the system is a largely unexamined field in Flanders. Based on our database of 200 standing waters in Flanders (macrophyte relevees and water quality data (VLINA/C97/02)), a series of waters with a large variation of nutrient contents and species richness will be selected. The main accent lies within the mesotrophic range. The different compartments, water - sediment (detritus - inorganic layer) - plant material and roots (divided in different growth forms) will be sampled during the growing season on a three-monthly basis. Biomass -production and N/P -content will be analysed and the nutrient dynamics of the aquatic system will be described. The relations between available and total nutrient concentrations on the one hand and biomass production, growth forms and species richness on the other give a good view on the limiting growth factors within the system determining the high nature values. To reduce the amount of variables the project will be carried out within a specific type of standing waters. Only shallow, freshwater ponds within the Campine area will be selected. Within this area, belonging to the sandy ecoregion of Flanders, a large natural variety of trophic levels and macrophyte vegetation is present.