Application of Flow-Ecology Analysis to Inform Prioritization for Stream Restoration and Management Actions

Abstract

A key challenge in managing flow alteration is determining the severity and pattern of alteration associated with the degradation of biological communities. Understanding these patterns helps managers prioritize locations for restoration and flow management actions. However, the choices made about how to use these flow-ecology relationships can have profound implications on management decisions (e.g., which biological endpoints, which thresholds, which seasonal flow components to use). We describe a process for using flow-ecology relationships to prioritize management actions that 1) Represents the most relevant components of the annual hydrograph, 2) Demonstrates an appropriate level of sensitivity in order to discriminate locations to inform decision making, 3) Aims to protect multiple biological assemblages, 4) Reduces misclassification of priority areas (i.e., error of omission). Our approach is based on the functional flows approach which uses multiple flow metrics that describe the frequency, timing, magnitude, duration, and rate of change of seasonal process-based components of the annual hydrograph. Using this approach, we performed a flow-ecology analysis of regional bioassessment data, through which we determined where flow alteration impacts biology and prioritized reaches for changes in flow management to protect aquatic resources in a highly urbanized region of southern California, where managing scarce water resources leads to difficult decisions about tradeoffs that require technical information. We identified three important functional flow metrics for each of two bioassessment indices, one based on benthic macroinvertebrates, and another based on benthic algae. Based on thresholds that describe levels of alteration as well as thresholds describing the probability of achieving a healthy biological condition, we compared nine biological threshold combinations for each index. We found instances of flow alteration that impact biological condition highly variable (0–100% of subbasins) between combinations and we present a method for finding the most appropriate combination for prioritizing locations for flow management. We apply the final thresholds to the study region and propose 16 subbasins of high priority for implementing flow management and restoration. Importantly, we show that focusing on a single biological group would result in biologically altered locations being effectively ignored.

Stream Algal Biomass Associations with Environmental Variables in a Temperate Rainforest

“…It is also possible that our observed negative relationship was due to lower attachment rates at higher velocities, thus slowing the accumulation of benthic algae [56,62]. In any case, the relationship between benthic algal biomass and water velocity is complex, as evidenced by interacting environmental factors, including water velocity and streambed stability [63,64].…”

Developing Ecological Flow Needs in a Highly Altered Region: Application of California Environmental Flows Framework in Southern California, USA

“…Long-term mean annual precipitation in the study region ranges from 722 to 299 mm (PRISM Climate Group, 2016). High priority areas where flow alteration may be associated with a biological decline were identified based on statewide bioassessment indices for macroinvertebrates and benthic algae (Irving et al, 2022). This paper focuses on a high priority area in lower Aliso Creek (see starred location in Figure 1) to illustrate the process and application of CEFF to develop ecological flow needs.…”

“…There may be other limiting factors including water quality and stream temperature, substrate composition, interactions with invasive species, food availability, among others, that should be considered in a comprehensive habitat suitability analysis. Moreover, future research could couple a comprehensive population viability model (Anderson et al, 2006;Shenton et al, 2012;Tonkin et al, 2018), models based on guilds of species that share similar flow needs (Merritt et al, 2010), or flow ecology models based on community responses (Irving et al, 2022;Mazor et al, 2018) with the eco-hydraulic analysis. Additionally, we utilized a more simplified hydraulic analysis to be applied at multiple high priority stream reaches in the South OC region.…”