Physical and microbial drivers of oxygen dynamics in the San Juan Islands

Speaker

Natasha R. Christman, University of WashingtonFollow

Presentation Abstract

Physical and Microbial Drivers of Dissolved Oxygen Dynamics in the San Juan Islands

Session Title

General oceanography

Conference Track

Habitat

Conference Name

Salish Sea Ecosystem Conference (2016 : Vancouver, B.C.)

Document Type

Event

Location

2016SSEC

Type of Presentation

Oral

Genre/Form

presentations (communicative events)

Contributing Repository

Digital content made available by University Archives, Heritage Resources, Western Libraries, Western Washington University.

Subjects – Topical (LCSH)

Water--Dissolved oxygen--Washington (State)--San Juan Islands; Water—Carbon dioxide content--Washington (State)--San Juan Islands; Microbial ecology--Washington (State)--San Juan Islands

Geographic Coverage

San Juan Islands (Wash.); Salish Sea (B.C. and Wash.)

Comments

Dissolved oxygen (DO) and carbon dioxide (CO2) dynamics in marine ecosystems are a product of both biological and physical forces. Through photosynthesis and respiration, microbial communities are the primary biological influence on DO and CO2 variability, while processes such as mixing and air-sea interaction may dominate as physical factors. This study investigates the relative contribution of microbial-mediated biogeochemical processes and their relationship to the physical influences of oxygen and CO2 in waters exposed to both incoming Pacific Ocean intrusions and Fraser River outflow: the San Juan Channel of the San Juan Archipelago. In a year-long oceanographic monitoring study, in situ respiration rates reveal that respiration activity in incoming low dissolved oxygen and high CO2 Pacific oceanic intrusions through the Strait is relatively low (~80μg DO/L/d) and much of the oxygen consumption occurs in the estuarine outflow overlying this bottom water. Additionally, manipulative experiments indicate that this oceanic input may be more carbon-limited and respond more rapidly to additions of organic carbon than in estuarine-sourced water. Consequently, this bottom water may be more susceptible to anthropogenic nutrient loading and may enhance localized respiration, furthering influencing dissolved oxygen and CO2 concentrations in the Salish Sea. In an intensive seven-week study of the channel in fall 2015, biological oxygen consumption in excess of water column mixing was found during periods of high primary production. However, following the fall transition from coastal upwelling to downwelling, oxygen at all stations in the San Juan Channel increased, indicating the physical shift of source waters. An abrupt shift of phytoplankton genera also co-occurred with the fall transition; the chain-forming diatom Chaetoceros spp. was dominant early in autumn, but then smaller diatoms became more abundant. These observations of dissolved oxygen dynamics in the San Juan Islands may help us understand the relative impacts of biological and physical forces in other areas of the Salish Sea and the contribution of human influence on these marine ecosystems.

Rights

This resource is displayed for educational purposes only and may be subject to U.S. and international copyright laws. For more information about rights or obtaining copies of this resource, please contact University Archives, Heritage Resources, Western Libraries, Western Washington University, Bellingham, WA 98225-9103, USA (360-650-7534; heritage.resources@wwu.edu) and refer to the collection name and identifier. Any materials cited must be attributed to the Salish Sea Ecosystem Conference Records, University Archives, Heritage Resources, Western Libraries, Western Washington University.

Type

Text

Language

English

Format

application/pdf