Aquatic and Land Interactions

The Research Program

The basic research program includes studies of the recovery of aquatic ecosystems from large disturbances and the interaction between riparian vegetation, large woody debris, and salmon carcasses in providing marine-derived nutrients to aquatic and riparian ecosystems. The applied research program includes studies of riparian ecosystem management and investigations of the cumulative effects of watershed management on riverine fish communities. Much of this work is currently being done in the area around Mount St. Helens volcano, where long-term monitoring continues to yield new insights into aquatic and riparian recovery after the 1980 eruptions. While volcanic eruptions are a part of the disturbance regime of the Pacific Northwest, similar types of catastrophic disturbances (e.g., fires, floods severe windstorms, and certain anthropogenic disturbances) can produce similar effects. Long-term monitoring has shown that aquatic ecosystems often undergo cyclic changes in productivity after large disturbances. Initially, aquatic productivity is depressed but a sharp rebound typically occurs that may lead to temporarily elevated fish populations within the first decade of the disturbance. Thereafter a decline related to heavy shading of streams by hardwoods and compensatory population regulation within the fish community may reduce productivity to unusually low levels for extended periods. Understanding these natural cycles helps resource managers avoid activities that impair ecosystem recovery processes and suggests ways in which recovery may actually be accelerated. Improved understanding of the cyclic nature of recovery from catastrophic disturbances also provides insight into the potential impacts of anthropogenic disturbances within the context of the natural disturbance regime. Results of the investigations will be directly applicable to the interpretation of disturbance history in Watershed Analysis.

The second basic research emphasis area—the interaction between riparian vegetation, large woody debris, and salmon carcasses—includes studies in Washington and Alaska. The subject area is so complex that investigations must be approached by a team of aquatic and terrestrial scientists who can integrate their combined knowledge to define the problem and produce effective studies. Previous research using stable isotope analyses have shown that more than 40% of the nutrients in the tissues of juvenile salmonids rearing in Washington can originate from adult salmon carcasses. In Alaska, this figure can be far greater. This nutrient contribution represents an important and generally underappreciated part of a stream’s trophic system. Synergism between biological and physical elements of the stream environment in controlling aquatic productivity has long been suspected but seldom documented. The research will determine what characteristics of riparian vegetation and large woody debris are needed for stream communities to derive maximum benefits from the marine nutrients contained in spawning salmon. Current investigations compare Washington streams, where adult salmon and woody debris are far below historical levels, with Alaska, where adult salmon and woody debris are very abundant.

A major emphasis of the applied research involves setting up a cooperative regional network of sites for studies of riparian ecosystem management. Restoration of riparian areas altered by past forest management practices is often identified by Watershed Analysis as a high priority for maintaining and rehabilitating aquatic ecosystem productivity. In the past, riparian restoration projects have often employed a trial-and-error approach that may be costly and ineffective. By supporting a regional network of research reference sites in which different aspects of riparian management are investigated as adaptive management trials, land owners are assisted in selecting riparian protection and restoration strategies appropriate to their particular situation. Additionally, this study will help resource managers in watersheds with mixed ownership to develop basin-wide restoration initiatives that better conserve aquatic ecosystems. Results will be directly applicable to designing riparian restoration programs under the Northwest Forest Plan and will also aid state, private industrial, and tribal land managers. The cooperative nature of the study leverages monitoring efforts over a wide range of ownerships and restoration approaches.

The second major applied investigation concerns the cumulative effects of watershed management on riverine fish communities. Emphasis is given to understanding the long-term effects of gravel and woody debris losses from stream channels on native fish biodiversity. Many streams in coastal Washington and Oregon have been converted from alluvially dominated channels to bedrock-dominated channels over a century of forest management. Presently there is a poor understanding of how these changes influence the diversity, functional composition (e.g., feeding guilds), and productivity of fish communities. Implementing restoration programs that ensure protection of biodiversity and productivity requires knowledge of channel characteristics needed to support native fish assemblages, and a key factor in maintaining a diversity of habitats is the structural complexity created by wood and coarse sediment.