Ecological assessment of river networks: From reach to catchment scale

Mathias Kuemmerlen,Peter Reichert,Rosi Siber,Nele Schuwirth

doi:10.1016/j.scitotenv.2018.09.019

Mathias Kuemmerlen, Peter Reichert + Show 2 more

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https://doi.org/10.1016/j.scitotenv.2018.09.019

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Abstract

Freshwater ecosystems are increasingly under threat as they are confronted with multiple anthropogenic impairments. This calls for comprehensive management strategies to counteract, or even prevent, long-term impacts on habitats and their biodiversity, as well as on their ecological functions and services. The basis for the efficient management and effective conservation of any ecosystem is sufficient knowledge on the state of the system and its response to external influence factors. In freshwater ecosystems, state information is currently drawn from ecological assessments at the reach or site scale. While these assessments are essential, they are not sufficient to assess the expected outcome of different river restoration strategies, because they do not account for important characteristics of the whole river network, such as habitat connectivity or headwater reachability. This is of particular importance for the spatial prioritization of restoration measures. River restoration could be supported best by integrative catchment-scale ecological assessments that are sensitive to the spatial arrangement of river reaches and barriers. Assessments at this scale are of increasing interest to environmental managers and conservation practitioners to prioritize restoration measures or to locate areas worth protecting. We present an approach based on decision support methods that integrates abiotic and biotic ecological assessments at the reach-scale and aggregates them spatially to describe the ecological state of entire catchments. This aggregation is based on spatial criteria that represent important ecological catchment properties, such as fish migration potential, resilience, fragmentation and habitat diversity in a spatially explicit way. We identify the most promising assessment criteria from different alternatives based on theoretical considerations and a comparison with biological indicators. Potential applications are discussed, particularly for supporting the strategic, long-term planning and spatial prioritization of restoration measures.

Highlights

Multiple methods have been implemented to assess freshwater ecosystems in different regions of the world (Buss et al, 2015; Ghetti, 1980; Metcalfe, 1989)
Compared to Reichert et al (2015), we extend the method in several aspects: a) in addition to morphology and nutrient concentration, we consider micropollutant concentration for the assessment of individual river reaches; b) we introduce spatial criteria for further ecological principles and test various versions to quantify them; c) we apply the method to three additional, larger catchments; and d) we use indices of biological condition for benthic macroinvertebrates and fish for comparison with the reach and catchment scale ecological state assessments
The IBCH index was significantly correlated with the chemical assessments in the same reach where the macroinvertebrates were sampled and to a lesser degree with the ecological state based on morphology, nutrients and micropollutants (Table 2)

Summary

Introduction

Multiple methods have been implemented to assess freshwater ecosystems in different regions of the world (Buss et al, 2015; Ghetti, 1980; Metcalfe, 1989). All have in common that they seek to determine the current state of the ecosystem, as to set a baseline against which past or future states can be compared to. This supports the identification of management alternatives to amend or overcome current impairments

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