Explaining the distribution of riverine macroinvertebrates : from autecological preferences to a catchment-wide perspective
The explanation of distributional patterns of riverine macroinvertebrates remains one of the major challenges in aquatic ecology. In addition to natural drivers such as geology, geomorphology and ecoregion influencing river characteristics and the composition of their communities, freshwaters are nowadays heavily impacted by various anthropogenic stressors operating on different spatial scales. The aquatic environment has been severely altered by i.a. point and diffuse sources of pollution habitat degradation and hydrological alterations. More specifically, environmental conditions have been impaired by changes in water chemistry due to nutrient enrichment and organic and/or toxic pollution, increased fine sediment input caused by changes in land use and lack of riparian vegetation as well as by changing flow velocities and substratum availability due to channel straightening. Beside these changes of the physical habitat also metapopulation dynamics have been strongly subjected to anthropogenic alterations. Recolonization processes have been made more difficult due to an increased construction of instream-barriers such as dams or weirs modified land use within the riverine environment, and persistent urbanization all of which promote the fragmentation of local populations. Especially habitats for sensitive species with high ecological demands are often degraded or lacking, limiting the number of source populations in the catchment. In order to reestablish near-natural habitat conditions and associated freshwater communities, the European Water Framework Directive (WFD, Directive 2000/60/EC) came into force in 2000. The directive aims at restoring degraded rivers in order to improve their ecological and chemical status, obligating river management to achieve ‘good’ ecological status until the year 2027 for all surface waters.Within this context, macroinvertebrates have long been used as indicators to assess the ecological status of a river in addition to fish and aquatic flora. The present thesis was mainly developed within the IMPACT research project and contributed to several tasks within an integrated modeling framework. The main objectives of the thesis were: (i) the characterization of species’ habitat preferences to develop a reach-scale habitat model, (ii) the development and application of a reach-scale habitat model to assess the effect of predicted abiotic changes on the macroinvertebrate community and ultimately biological assessment and (iii) the development and application of a Species Distribution Model (SDM) to identify source populations which are used as input for subsequent dispersal modeling in order to assess the (re)-colonization potential of selected species within the catchment.