PARENT SESSION
Contributed Oral Session 133: Biogeochemistry of Streams and Wetlands
Thursday, August 11, 1:30 PM - 5:00 PM, Meeting Room 516 C, Level 5, Palais des congrès de Montréal

How much logging is too much? The impact of coastal logging on aquatic inputs to nearshore marine systems.

Tallis, Heather^*,1, Gray, Elizabeth², ¹ University of Washington, Seattle, WA² The Nature Conservancy, Seattle, WA

ABSTRACT- Although it is widely appreciated that logging can alter stream and river water quality, the extent to which these impacts persist in coastal oceans is unknown. Understanding the importance of land use effects to marine systems is vital for the successful alignment of terrestrial, aquatic and marine management. We conducted a large-scale study of 15 watersheds and their river and plume chemistry on the Olympic Peninsula (WA). We show that summer river concentrations of dissolved organic carbon (DOC), nitrate, ammonia, phosphate, total nitrogen (N), and total phosphorus (P) and N:P increased with road density or transitional forest cover (indicators of logging intensity). Comparing low-intensity logging to high intensity logging yielded observed impacts that were dramatic, ranging from a tenfold increase in DOC, to a 7-fold increase in phosphate, and a switch in the major form of N exported driven by a 45-fold increase in nitrate concentration. We identified a threshold in road density (1.7 km road 1000 km^-2 watershed) related to the change from biologically unavailable dissolved organic nitrogen (low logging watersheds) to biologically available nitrate (highly logged watersheds) in rivers. This is the first indication of ecosystem N-saturation driven by timber harvest practices. We also show that transitional forest cover near rivers (within 120 m) had a disproportionately strong influence on nitrate concentrations. In the nearshore ocean, summer coastal upwelling swamped the logging effects on N, but not on DOC. Since logging affects the coastal ocean, marine conservation within the Olympic Coast National Marine Sanctuary may require changes in upstream management for maintenance of ecosystem processes.

Key words: cross-system linkages, integrated management, landscape, biogeochemistry