Developing a broader scientific foundation for river restoration: Columbia River food webs

Abstract

Well-functioning food webs are fundamental for sustaining rivers as ecosystems and maintaining associated aquatic and terrestrial communities. The current emphasis on restoring habitat structure--without explicitly considering food webs--has been less successful than hoped in terms of enhancing the status of targeted species and often overlooks important constraints on ecologically effective restoration. We identify three priority food web-related issues that potentially impede successful river restoration: uncertainty about habitat carrying capacity, proliferation of chemicals and contaminants, and emergence of hybrid food webs containing a mixture of native and invasive species. Additionally, there is the need to place these food web considerations in a broad temporal and spatial framework by understanding the consequences of altered nutrient, organic matter (energy), water, and thermal sources and flows, reconnecting critical habitats and their food webs, and restoring for changing environments. As an illustration, we discuss how the Columbia River Basin, site of one of the largest aquatic/riparian restoration programs in the United States, would benefit from implementing a food web perspective. A food web perspective for the Columbia River would complement ongoing approaches and enhance the ability to meet the vision and legal obligations of the US Endangered Species Act, the Northwest Power Act (Fish and Wildlife Program), and federal treaties with Northwest Indian Tribes while meeting fundamental needs for improved river management.

Fig. 1.

In addition to the construction of major dams, the Columbia River Basin has undergone substantial transformations in many other ways. Examples include (A) blocking of anadromous fish passage over large areas (StreamNet), (B) substantial releases (annual average of 2006–2012) of hatchery-raised fish (Fish Passage Center, Portland, OR), (C) widespread application of pesticides (246 compounds evaluated; average of 1999–2004) and construction of wastewater treatment plants, and (D) establishment of numerous nonnative aquatic species (note that the number and distribution of nonnative riparian species are not known). White areas, outside Columbia River Basin.

Fig. 2.

Food web structure in the Hanford Reach of the Columbia River (considered a relatively well-known site). The weak food web resolution illustrates the lack of fundamental knowledge. Note the prevalence of nonnative species. The depicted food web is only a rudimentary subset of the actual web, despite being a well-studied site; there is little empirical understanding of the diversity of food web elements and critical linkages. The basal nodes of the food web—terrestrial plants, periphyton, detrital-associated organisms, aquatic insects, and zooplankton—are aggregates of a huge diversity of organisms; in contrast, the higher nodes are usually composed of single species. Red, primary producers; orange, primary consumers; yellow, secondary consumers; green, tertiary consumers (created in Network3D; RJ Williams, 2010, Network3D Software; Microsoft). *Taxonomic groups containing some nonnative species. **Nonnative species.

Fig. 3.

Hundreds of nonnative aquatic species are now established in the Columbia River Basin, and many have changed food webs in unanticipated and unwanted ways by shifting predation pressure or fundamentally altering fluxes of energy and nutrients. (A) M. diluviana and (B) American shad (A. sapidissima) are abundant and important competitors with planktivorous salmonids and potentially serve as a nonnative energy source, thus expanding predator populations and increasing predation mortality on resident and anadromous salmonids. Furthermore, altered environmental conditions are allowing the expansion of many native predators, including (C) Caspian terns (H. caspia), thereby directly altering food webs and increasing predation on native salmonids (48, 49). Photos courtesy of (A) www.flickr.com/photos/wontolla_jcb/2475661498/, (B) D. Hasselman, and (C) Bird Research Northwest.