Dissertation

Putting Intermittent Rivers on the Map: Integrating Non-Perennial Rivers and Streams in the Sustainable Management of Freshwater Ecosystems

Messager, Mathis Loïc

2024

Overview

Virtually every river network on Earth includes non-perennial rivers and streams (NPRs) that periodically cease to flow or dry. The recurrence of flowing, non-flowing and dry phases that characterize NPRs uniquely supports high biodiversity and biogeochemical cycles in entire river networks. Consequently, changing these hydrological cycles can threaten the integrity of riverine ecosystems and the people that depend on them for their livelihood and culture. Despite their prevalence and importance, NPRs are largely excluded from management practices, conservation laws, and scientific research that have been tailored to perennial rivers. This bias, which stems from a historical lack of consideration for the value and distinctiveness of NPRs, is resulting in their rapid degradation. The aim of this thesis is to advance our understanding of the global prevalence and diversity of NPRs, and to improve their integration in river policy and sustainable management. Leveraging an interdisciplinary perspective integrating hydrology, ecology, geography, and data science, this thesis addresses three main objectives through four articles (Chapters 2 to 5).i)Chapter 2 and 3 provide the first robust quantitative estimate of the prevalence, distribution, and diversity of NPRs worldwide. Using a machine learning model informed by global data on hydrology, climate, geology, and land cover, Chapter 2 reveals that water ceases to flow for at least one day per year along 51%–60% of the world’s rivers by length. This finding demonstrates that non-perennial rivers and streams are the rule rather than the exception on Earth, and that they occur within all climates and biomes, and on every continent. Chapter 3 identifies nine hydrological types of NPRs globally which differ in how often, how long, when and why they stop to flow.ii)Chapter 4 highlights the inadequate protection of NPRs by environmental protection laws. Through a case study of regulatory maps defining which watercourses are protected under the Water Law in France, this chapter sheds light on the socio-political factors influencing regulatory cartography, exposes the disproportionate exclusion of NPRs from regulatory frameworks, and discusses the implications of this exclusion for river network integrity.iii)Chapter 5 introduces a novel conceptual and operational framework to enhance the effectiveness of flow management programs to sustain freshwater ecosystems (i.e., environmental flows) in river networks with a high prevalence of NPRs. It proposes to broaden the set of ecological processes integrated into the design, implementation, and monitoring of environmental flows with the end goal of better protecting the distinct ecological structure and dynamics of NPRs.This thesis challenges the prevailing conceptual models of river ecosystems by demonstrating the global prevalence and diversity of NPRs, and by supporting their integration into science, policy, and management frameworks. In doing so, it contributes to an ongoing paradigm shift towards an integrated view of river networks. This integrated view involves studying and managing all reaches, their floodplain, and contributing catchment as a dynamically interconnected meta-ecosystem whose components span the aquatic-terrestrial continuum.

• Publisher: ProQuest Dissertations & Theses
• Subject: Ecology / Environmental management / Public policy / Water Resources Management
• ISBN: 9798304951067