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TERRESTRIAL AND MARINE SOURCES OF NUTRIENTS TO AN OREGON COASTAL RIVER
Citation:
Compton, J E., M R. Church, AND S. T. Larned. TERRESTRIAL AND MARINE SOURCES OF NUTRIENTS TO AN OREGON COASTAL RIVER. Presented at 10th Annual Cary Conference, Millbrook, NY, April 29-May 1, 2003.
Description:
In the Pacific Northwest of North America, anadromous fish can transport significant quantities of nutrients and energy from the ocean to the watersheds where they return, reproduce and die. In addition, the widespread distribution of N2-fixing alders (Alnus spp.) can influence stream nitrogen status. To understand the relative magnitude of terrestrial and marine nutrient supply, we compared watershed export of N, C and P with the delivery of these elements in returning salmonids. We measured dissolved nutrient concentrations and streamflow in the Salmon River in the Oregon Coast Range during the year 2000. Dissolved hydrologic export from the watershed was 9.7 kg N ha-1 yr-1, 16 kg C ha-1 yr-1, and 0.19 kg P ha-1 yr-1. The proportion of red alder (Alnus rubra) plus mixed alder-conifer vegetation cover explained approximately 76% of the variation in watershed N export across sub-watersheds within the basin. Using population estimates of returning coho and chinook, we estimate the element flux via these predominant salmon species. The ratio of terrestrial to marine supply is very high (167, 67 and 28 for N, C, and P respectively), indicating that under present conditions, these elements are largely supplied from the watershed. Present-day salmon runs in coastal Oregon are approximately 1-5% of historic runs, and therefore marine-derived N, C and P were relatively more important before the decline of salmon runs. Consideration of the form and timing of nutrient supply, as well as the mode of entry into stream food webs and inherent stream nutrient limitation, are important in light of new efforts to augment stream nutrients as an aid in salmon recovery.