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Doctoral thesis, 2018

Ecosystem functioning in streams under pressure : understanding the roles of biotic, abiotic and spatial drivers

Truchy, Amélie

Abstract

What will happen if human populations are not able to rely on Earth’s ecosystems to deliver fundamental benefits in a near future? Stream ecosystems provide several essential services to human civilizations, but are currently under threat from multiple anthropogenic pressures. These pressures give rise to stressors that impact biodiversity, ecosystem functioning, and ultimately ecosystem service delivery from streams. Based on a novel synthesis of the literature, I developed a framework integrating the roles that communities, environment and spatial drivers play in regulating ecosystem processes, further applied in field studies and an experiment. In field studies, I assessed the variation in community structure of four taxonomic groups, and several ecosystem processes, along gradients of increasing pressure from agriculture, river regulation and forestry management. Ecosystem processes frequently varied along the pressure gradients, but the form of response typically contrasted, reflecting the complex interactions of abiotic and biotic factors that are into play. Environmental variables were shown to impact ecosystem processes either directly or indirectly through community-mediated responses. Changes in communities along a gradient depended on the associated stressors, the organism groups and the spatial scale at which they operate, and species traits were sometimes more responsive than species composition. Finally, my results from both the field and experimental studies highlight the importance of local and regional spatial scales for regulating the composition of communities and the processes they regulate, in particular for microorganisms. Although policy frameworks mention the importance of ecosystem functioning in maintaining ecosystem services, the use of abiotic and taxonomic variables as indicators of human impacts on ecosystems remain the most common approach. My results reveal that community structure and specific aspects of ecosystem functioning might not always be strongly correlated, highlighting the importance of incorporating quantification of ecosystem processes in biomonitoring. Additionally, my results point towards the need to develop more spatially explicit biomonitoring schemes, able to account for position of sampling sites in the landscape.

Keywords

Abiotic factors, Anthropogenic stressors, Community ecology, Ecosystem functioning, Habitat patchiness, Pressure gradient, Recovery, Spatial connectivity, Species traits

Published in

Acta Universitatis Agriculturae Sueciae
2018, number: 2018:1
ISBN: 978-91-7760-142-5, eISBN: 978-91-7760-143-2
Publisher: Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences