Accounting for Uncertainty in Regional Flow–Ecology Relationships

Betsy Morgan,Belize Lane

doi:10.1061/(asce)wr.1943-5452.0001533

Abstract

Flow–ecology relationships are critical for developing and adaptively managing environmental flows. However, uncertainty often arises from data limitations and an incomplete understanding of the spatial and temporal attributes inherent to each relationship. Accounting for sources of uncertainty is critical given the mounting interest in implementing environmental flows at large scales, often with limited information. We used the South Fork Eel River watershed in northern California as a case study to demonstrate how data gaps and uncertainty in flow–ecology relationships may be better quantified. A rigorous literature review revealed that few flow–ecology relationships related directly to the flow regime, and none spanned the full range of hydrologic or geomorphic variability exhibited across the watershed. Identified data gaps informed several sensitivity analyses within a Bayesian network model which showed that the modeled ecological outcome differed by as much as 50% depending on the type and magnitude of uncertainty. This study presents a general regional framework for quantifying spatial and temporal data gaps that can be applied to other watersheds and information types to improve representation of uncertainty in flow–ecology relationships and to inform environmental flow design.

Highlights

It is understood widely that key components of the natural flow regime and associated physical conditions and processes, such as water temperature and sediment regime, are critical for sustaining native aquatic species (Poff et al 1997; Yarnell et al 2020; Gasith and Resh 1999)
Study findings highlight the challenge of using empirical flow–ecology relationships developed for a subset of species and physical conditions to develop comprehensive ecosystemscale environmental flows, which increasingly is required by holistic approaches (Horne et al 2017; Mierau et al 2018; Yarnell et al 2020)
Given the mounting need to establish environmental flows over large areas based on limited data, flow–ecology relationships often are extrapolated outside of the conditions under which they were developed

Summary

Introduction

It is understood widely that key components of the natural flow regime and associated physical conditions and processes, such as water temperature and sediment regime, are critical for sustaining native aquatic species (Poff et al 1997; Yarnell et al 2020; Gasith and Resh 1999). All approaches are similar in that ecological outcomes are characterized in part by flow–ecology relationships— models linking ecological characteristics to the flow regime, either directly or through mediating physical habitat conditions (e.g., sediment composition, water temperature, and hydraulics) or biological factors (e.g., food web dynamics) (Horne et al 2019; Wheeler et al 2018). Flow–ecology relatsionships are fundamental for developing and adaptively managing environmental flows (Horne et al 2018)

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