Presentation Abstract

Bellingham Bay, a shallow, urbanized embayment in north Puget Sound, is experiencing increasing seasonal hypoxia. But, rates of sedimentary geochemical processes that might contribute to this change are not well quantified. This project explored the relationships between sedimentary biogeochemical processes, nutrient fluxes, and oxygen consumption in Bellingham Bay. Working with the Washington State Department of Ecology, we sampled 25 stations throughout the bay, and measured fluxes of dissolved oxygen, dissolved inorganic nitrogen, dissolved inorganic phosphorus, silicate, and dissolved inorganic carbon between sediment and overlying water. We observed decreases in the fluxes of DO, DIC, and DIN with station depth, suggesting that more organic carbon and nitrogen loading is occurring near shore. DIN:DIC and DIP:DIC flux ratios were generally less than those predicted by the Redfield ratio, suggesting that the sediment is a net sink of nitrogen and phosphorus in this coastal embayment. We also found that DO:DIC flux ratio was generally less than the expected 1:1 ratio, indicating production and storage of reduced species such as sulfide, through microbial anaerobic respiration. Further, comparison with water column oxygen consumption rates indicates that total oxygen consumption by the sediment roughly equals oxygen consumption by the water column. These findings suggest that the benthos may play at least two roles in regulating seasonal hypoxia and eutrophication: (1) as a sink for nutrients, which could have some mitigating effect on eutrophication, and (2) as a consumer of water column dissolved oxygen, which could exacerbate seasonal hypoxia. These findings are a crucial step towards linking sedimentary biogeochemical processes with eutrophication and hypoxia in Bellingham Bay.

Session Title

Interdisciplinary Approaches to Understanding Eutrophication and Over-enrichment of Nutrients in Puget Sound and Effects on Marine Species

Keywords

Sedimentary biogeochemistry, Oxygen consumption, Nutrient cycling, Bellingham Bay

Conference Track

SSE16: Long-Term Monitoring of Salish Sea Ecosystems

Conference Name

Salish Sea Ecosystem Conference (Seattle, WA : 2018)

Document Type

Event

SSEC Identifier

SSE16-430

Start Date

6-4-2018 8:45 AM

End Date

6-4-2018 9:00 AM

Type of Presentation

Oral

Contributing Repository

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

Geographic Coverage

Salish Sea (B.C. and Wash.)

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

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Apr 6th, 8:45 AM Apr 6th, 9:00 AM

Influence of sedimentary biogeochemistry on oxygen consumption and nutrient cycling in Bellingham Bay, Washington

Bellingham Bay, a shallow, urbanized embayment in north Puget Sound, is experiencing increasing seasonal hypoxia. But, rates of sedimentary geochemical processes that might contribute to this change are not well quantified. This project explored the relationships between sedimentary biogeochemical processes, nutrient fluxes, and oxygen consumption in Bellingham Bay. Working with the Washington State Department of Ecology, we sampled 25 stations throughout the bay, and measured fluxes of dissolved oxygen, dissolved inorganic nitrogen, dissolved inorganic phosphorus, silicate, and dissolved inorganic carbon between sediment and overlying water. We observed decreases in the fluxes of DO, DIC, and DIN with station depth, suggesting that more organic carbon and nitrogen loading is occurring near shore. DIN:DIC and DIP:DIC flux ratios were generally less than those predicted by the Redfield ratio, suggesting that the sediment is a net sink of nitrogen and phosphorus in this coastal embayment. We also found that DO:DIC flux ratio was generally less than the expected 1:1 ratio, indicating production and storage of reduced species such as sulfide, through microbial anaerobic respiration. Further, comparison with water column oxygen consumption rates indicates that total oxygen consumption by the sediment roughly equals oxygen consumption by the water column. These findings suggest that the benthos may play at least two roles in regulating seasonal hypoxia and eutrophication: (1) as a sink for nutrients, which could have some mitigating effect on eutrophication, and (2) as a consumer of water column dissolved oxygen, which could exacerbate seasonal hypoxia. These findings are a crucial step towards linking sedimentary biogeochemical processes with eutrophication and hypoxia in Bellingham Bay.