Abstract
River biota are affected by global reach-scale pressures, but most approaches for predicting biota of rivers focus on river reach or segment scale processes and habitats. Moreover, these approaches do not consider long-term morphological changes that affect habitat conditions. In this study, a modelling framework was further developed and tested to assess the effect of pressures at different spatial scales on reach-scale habitat conditions and biota. Ecohydrological and 1D hydrodynamic models were used to predict discharge and water quality at the catchment scale and the resulting water level at the downstream end of a study reach. Long-term reach morphology was modelled using empirical regime equations, meander migration and 2D morphodynamic models. The respective flow and substrate conditions in the study reach were predicted using a 2D hydrodynamic model, and the suitability of these habitats was assessed with novel habitat models. In addition, dispersal models for fish and macroinvertebrates were developed to assess the re-colonization potential and to finally compare habitat suitability and the availability / ability of species to colonize these habitats. Applicability was tested and model performance was assessed by comparing observed and predicted conditions in the lowland Treene River in northern Germany. Technically, it was possible to link the different models, but future applications would benefit from the development of open source software for all modelling steps to enable fully automated model runs. Future research needs concern the physical modelling of long-term morphodynamics, feedback of biota (e.g., macrophytes) on abiotic habitat conditions, species interactions, and empirical data on the hydraulic habitat suitability and dispersal abilities of macroinvertebrates. The modelling framework is flexible and allows for including additional models and investigating different research and management questions, e.g., in climate impact research as well as river restoration and management.
Highlights
River biota are affected by anthropogenic pressures acting at different spatial scales, ranging from global climate and catchment scale hydrological changes [1], catchment scale water quality pressures including point and diffuse source pollution such as nutrients, pesticides, and fine sediment [2] to reach-scale hydromorphological alterations such as channelization
Several empirical studies indicate that large-scale pressures, as measured by proxies such as catchment land use, can be more important in shaping macroinvertebrate and fish communities compared to pressures at smaller spatial scales [4,5,6,7,8,9]
Model performance was highest for peak discharges and the recession phase and lower for long dry periods and the resaturation phase [75], i.e., at low discharges, which are of special importance for biota
Summary
River biota are affected by anthropogenic pressures acting at different spatial scales, ranging from global climate and catchment scale hydrological changes [1], catchment scale water quality pressures including point and diffuse source pollution such as nutrients, pesticides, and fine sediment [2] to reach-scale hydromorphological alterations such as channelization. In addition to these changes in abiotic habitat conditions, the biota of rivers depends on the species pool available for re-colonization. Complementary modelling could help to assess the importance of different pressures by coupling models that predict the effect of these pressures on abiotic habitat conditions and biota
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