A Modelling Framework to Assess the Effect of Pressures on River Abiotic Habitat Conditions and Biota

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.

Eco-hydrologic model cascades: Simulating land use and climate change impacts on hydrology, hydraulics and habitats for fish and macroinvertebrates

“…The single parts of the applied integrated modelling framework developed by Kail et al (2015) are presented briefly step-by-step in the order of decreasing spatial scale (Table 1) and the model cascade is then described in detail in Section 2.3.…”

“…2B). It was considered near-natural since it is heavily meandering, has a mean bankfull width (10.9 m) and depth (1.4 m) typical of a natural river with highly cohesive river banks (80-100% silt/clay content) and a bankfull discharge of 6.0 m 3 /s (Kail et al, 2015). It differs from fully natural reaches since bed-material is pure sand with a D 50 of 0.16 mm, whilst gravel-patches would be present in the natural state, and the reach is bordered by pasture instead of naturally occurring floodplain forest (Pottgiesser and Sommerhäuser, 2008).…”

“…The suitability of these habitats for macroinvertebrates was assessed based on habitat models . This modelling cascade was recently further developed by including morphological and dispersal models by Kail et al (2015). In this model framework, fish were considered besides macroinvertebrates to test the applicability of such an integrated modelling framework for different organism groups.…”

“…This modelling framework consists of separate models for the major processes and depicts the different habitat characteristics of fish and macroinvertebrates. The principal applicability of their modelling framework was demonstrated in Kail et al (2015).…”

“…Therefore, this study used the modelling framework presented by Kail et al (2015) to investigate consecutive impacts of land use and climate change on hydrology, hydrodynamic and biota. Two different process chains were analysed for considering the specific habitat preferences of fish and macroinvertebrates, respectively.…”