Water Resources Research Act Program

Details for Project ID 2004CA91B

Using Marine Derived Nitrogen in Tree Rings to Assess Nutrient Flux and Salmon Escapement

Institute: California
Year Established: 2004 Start Date: 2004-03-01 End Date: 2005-02-28
Total Federal Funds: $14,276 Total Non-Federal Funds: $29,331

Principal Investigators: Michael Johnson, Michael Johnson

Project Summary: EXECUTIVE SUMMARY Statement of critical state water research problem: Historically, Californias anadromous salmon delivered substantial amounts of marine derived nutrients to their natal streams where they returned to spawn. Nutrients released from spawned-out carcasses were incorporated into both the aquatic and terrestrial environments and ultimately helped create more productive spawning and rearing grounds. The reduction or extirpation of anadromous salmon from many basins has likely altered critical nutrient cycling processes within and between the aquatic and terrestrial ecosystems. A major focus of current salmonid restoration efforts is the amelioration of both instream and riparian habitat. The importance of streamside riparian zones to salmonid production has been well demonstrated in California and elsewhere. Most attention, however, has focused on the value of riparian zones as sources of shade, sediment filtration, woody debris and other material. Comparatively little is known about the critical role riparian zones play in cycling energy and material between the aquatic and terrestrial ecosystems. Knowledge concerning current and historic functionality and connectivity between the two adjacent systems will maximize restoration efforts for wildlife in both habitats. Research approach: We propose to examine current and historic relationships between salmon spawning and riparian growth and function using natural abundance stable nitrogen isotope ratios. Annual changes in stable nitrogen isotopes will be determined from increment core (tree ring) samples collected from live trees and correlated to salmon abundance, tree growth, and stream proximity. Our investigation will take place at study sites within the Klamath (Bogus Creek) and Sacramento (Butte Creek) watersheds where suitably mature riparian trees and historic salmon escapement data are both available. Anticipated outcome of the study: We expect that marine derived nitrogen transferred to receiving streams by anadromous Pacific salmon will be detectable in annual tree ring samples extracted from riparian conifers. Uptake and utilization of this nitrogen source by riparian trees is expected to decrease with increased distance from the stream channel. Fluctuations in annual tree growth and ring nitrogen isotope ratios should correlate with records of salmon escapement. Comparisons between tree growth and salmonid returns will help identify temporal lags in nutrient delivery and incorporation. Potential Benefits: This study will improve our understanding of the scale and movement of marine derived nutrients and potentially critical ecological feedbacks associated with anadromous salmon. Identifying nutrient linkages between salmon and riparian productivity will greatly assist restoration efforts in many California watersheds. Furthermore, if a predictable relationship exists between tree ring nitrogen levels and salmonid escapement, it will be possible to reconstruct historic returns for watersheds where old growth trees still exist and escapement data do not.