PARENT SESSION
Oral Session #76: Ecosystem Ecology: Larger scale processes, geomorphology, soils.
Presiding: W. Straw
Thursday, August 8. 9:00 AM to 11:30 AM. Gila Meeting Room, TCC.

Nutrient use efficiency by phytoplankton in a coastal upwelling ecosystem: Patterns along the Oregon Coast .

CHAN, FRANCIS^*,1, MENGE, BRUCE¹, NIELSEN, KARINA, LUBCHENCO, JANE¹, ¹ Partnership for the Interdisciplinary Studies of Coastal Oceans, Oregon State University, Corvallis, OR

ABSTRACT- The productivity of aquatic and terrestrial ecosystems reflects the supply of limiting nutrient(s) and the efficiency with which available nutrients are used in plant growth. Conceptual and empirical models of nutrient use efficiency (NUE) developed for terrestrial ecosystems point to strong general declines in NUE with increasing nutrient availability. These models provide an important framework for understanding cross-system variations in terrestrial NUE and their responses to nutrient enrichment. In contrast, the role of NUE in mediating aquatic productivity, and cross-system variations in aquatic NUE have, with few exceptions, remained poorly characterized. In the coastal waters of the California Current System, seasonal upwelling of nutrient-rich waters results in spatially and temporally heterogeneous patterns in water column nitrogen (N) content. We monitored the growing season response of phytoplankton biomass to N-availability along the entire extent of the Oregon coast. In these near-shore waters, episodic increases of phytoplankton biomass resulted in chlorophyll a concentrations that range upwards of 100 ug/l. Salinity measurements and mass balance of water column N-pools do not point to riverine N-inputs or physical aggregations processes or as the causes of high near-shore phytoplankton biomass. Comparisons of chlorophyll a and total nitrogen concentrations suggest that abundant phytoplankton biomass reflects both increased N-availability and elevated values of NUE. Consideration of NUE and the mechanisms that regulate its variation may offer important insights into the control on nutrient-limitation in aquatic ecosystems.

KEY WORDS: upwelling , nitrogen, nutrient-use-efficiency, phytoplankton