The ditch networks in polder landscapes are a prime example of aquatic ecosystems where biodiversity and ecology are under threat because of intense agricultural land use. These connected water systems constitute a large part of the fresh water surface of the Netherlands. Due to their connected nature, conservation and management of biodiversity may benefit from a more regional perspective. Within this thesis I studied the biodiversity and environmental quality of 21 polder landscapes in a region in the west of the Netherlands. My work (Chapter 2, Chapter 3) confirms previous work showing that high dissimilarity in community composition between ditch reaches across different species groups exists. Furthermore, I show that different polder landscapes harbour different communities (Chapter 2) and these are complementary to eachother. I found land use and nutrient loading to be important predictors of biodiversity across levels of spatial scale (local to regional) and across species groups (Chapter 2 and 3). Eutrophication of aquatic systems can lead to changing nutrient incorporation in stoichiometrically flexible primary producers. In chapter 4 I illustrate that aquatic plants are partly flexible in their nutrient incorporation. I also showed that different plants may exhibit a different tissue elemental content under similar environmental nutrient conditions. Consumers tend to be less flexible, leading to elemental mismatches between producers and their consumers that impacts consumer community structure and functioning. In chapter 5 I study how elemental mismatches impact consumer community composition using a phytoplankton-zooplankton community as a model system. Here I showed that consumer communities cope with mismatches in phytoplankton food quality through both shifts in species composition and intra-specific elemental plasticity. Also, producer nutrient enrichment led to an enrichment of sedimenting detrital matter, leading to an enriched sediment. Sediment enrichment is an important part of the natural ...