Adaptive management of large‐scale ecosystem restoration: increasing certainty of habitat outcomes in the Columbia River Estuary, U.S.A.

Abstract

Ecological restoration programs in dynamic coastal environments can benefit from adaptive management, including an iterative process for identifying and addressing critical uncertainties. We highlight key developments under the three pillars that have increased the rate of restoration by the Columbia Estuary Ecosystem Restoration Program (CEERP) over 20 years: science, coordination, and management. We show how such programs can be institutionalized to ensure that estuary ecosystems are better understood, conserved, and restored. The principal conservation effort under CEERP is to reconnect historical floodplain wetlands to the mainstem. The program also supports other restoration actions that demonstrate a high potential to benefit ecosystem function and endangered salmon populations; however, there is greater uncertainty regarding these less-utilized techniques. Through adaptive management, we address technical uncertainty regarding benefits to the environmental resource and programmatic uncertainty pertaining to decision-making. Here, we examine three periods of CEERP growth to establish how complementary research and restoration actions have improved program outcomes over time. We highlight the tools and processes that were developed and integrated into the program to refine program strategy, improve project design, and maximize ecological benefits. CEERP supported 77 restoration projects and reconnected over 7,000 acres of floodplain habitat to the lower Columbia River between 2004 and 2021. Building on these successes, we outline current plans to better engage landowners and local communities, solicit new project types, and maintain enough flexibility within the program to adapt to new priorities.

Export of macroinvertebrate prey from tidal freshwater wetlands provides a significant energy subsidy for outmigrating juvenile salmon

“…In response, a broad campaign has been initiated to restore connectivity between degraded LCRE wetlands and the mainstem river [39,41]. Many of these restoration projects are explicitly designed to improve access for juvenile Pacific salmon to productive wetland interiors [40,89], and restoration has indeed increased hydrological connections and opportunities for juvenile salmon at many locations in the LCRE [39,41,90]. Our study of prey flux and transport rates, though, shows ecological benefits of restoring wetlands exceed their physical boundaries.…”

“…Since the late 1800s, almost three-quarters of the total historical area of vegetated tidal wetlands of the LCRE have been lost to diking, filling, and bank hardening, combined with flow regulation and other modifications [37,38,88]. In response, a broad campaign has been initiated to restore connectivity between degraded LCRE wetlands and the mainstem river [39,41]. Many of these restoration projects are explicitly designed to improve access for juvenile Pacific salmon to productive wetland interiors [40,89], and restoration has indeed increased hydrological connections and opportunities for juvenile salmon at many locations in the LCRE [39,41,90].…”

“…This highly regulated river system once supported extensive TFW habitats extending from near the estuary mouth to over 235 km upstream [37,38]. To remedy this loss, habitat restoration activities in the LCRE over the last several decades have emphasized increasing hydrological connectivity to enhance opportunity for juvenile salmon to access wetland interiors, as well as enhance export of prey material to the mainstem [39][40][41].…”

Life in the Fast Lane: Feeding and Growth of Juvenile Steelhead and Chinook Salmon in Main‐Stem Habitats of the Columbia River Estuary

“…In the CRE, thousands of acres of former tidal marsh habitat have been restored specifically to benefit juvenile salmon (Thom et al. 2011; Littles et al., in press). An underlying premise of this restoration is that prey such as chironomid insects (nonbiting midges) produced in restored tidal wetlands would be exported to the main channel, where they would be available to migrating salmon.…”

“…We accomplished these objectives by collecting juvenile salmon in the main channel at four sites that spanned 195 km of the CRE during the spring out‐migration in two highly contrasting years. We expected that salmon would feed as they moved downstream, and we expected higher gut fullness and more wetland‐produced prey (e.g., chironomids) in diets of fish sampled lower in the CRE, where both extant and restored wetlands are more abundant (Marcoe and Pilson 2017; Littles et al., in press). We were uncertain whether we could document growth given the extremely short time (<1 week) it takes salmon to traverse the CRE.…”