Go with the flow Unravelling the ecological mechanisms of dispersal and colonization by aquatic macroinvertebrates in restored lowland streams

To some people from Amsterdam this may come as a surprise, but the Netherlands is home to many natural freshwater streams. These Dutch lowland streams are indispensable to us, as they provide resources, such as drinking water and fish, and serve functions, such as the irrigation of agricultural crops and drainage of wastewater. In the past, anthropogenic alterations enhanced these functions, but this led to an overall deterioration of water quality and a lack of habitats for stream inhabiting organisms. Therefore, many species disappeared from the freshwater streams. Restoration efforts were made, but unfortunately, populations of aquatic fauna do not return as quickly as anticipated. Until now, it remains mostly unclear why the diverse group of macroinvertebrates (e.g. insects, snails and mussels) does not recolonize these restored streams. In this thesis, we explored the ecological mechanisms behind the dispersal and subsequent colonization of aquatic macroinvertebrates in restored lowland streams. Long-distance overland dispersal can only take place if species have specific traits that increase their dispersal capacity, while seasonality and population size trigger short-distance dispersal. Colonization of recently restored stream trajectories that are well connected to regional source pools with large populations of macroinvertebrates, can be very rapid. After the macroinvertebrates reach the newly restored habitat, local environmental factors play a role in their survival and fitness rates. Our findings aid a more complete understanding of community assembly in lowland streams and recolonization of restored stream reaches, and meanwhile direct towards specific implications to make ecological restoration more successful.