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Ecology-PSAMP 2004 Hood Canal Focus Study and 1932-2005 Historical Data Summary for the Hood Canal Dissolved Oxygen Program

Sediment monitoring stations sampled in Hood Canal from 1952  through 2005.

Environmental Management Application

The 2004 Hood Canal focus study and 1932-2005 follow-up historical data summary document geographic differences, changes over time, and relationships between sediment quality, sediment-dwelling invertebrate communities, and dissolved oxygen levels in Hood Canal. This work provides data and information to environmental managers and scientists addressing the low dissolved oxygen problem in Hood Canal as part of the Hood Canal Dissolved Oxygen Program (HCDOP).

Background

In 2004, Ecology conducted a focus study in Hood Canal, with the goal of evaluating the spatial extent and geographic patterns of sediment quality degredation throughout the Canal. Samples collected at 30 locations were analyzed for a suite of Sediment Quality Triad parameters (list of parameters) to determine the concentrations of potentially toxic chemicals, the degree of response in a laboratory toxicity test, and the composition of resident sediment-dwelling invertebrates. Levels of near-bottom dissolved oxygen were also measured at each station.

Water column monitoring stations sampled in Hood Canal from 1932  through 2005.

Ecology then entered into a collaborative effort with Dr. David Shull of Western Washington University in 2005 as part of the HCDOP Integrated Assessment & Modeling Study. This project combined the 2004 Hood Canal focus study data with historical Hood Canal sediment and water column data collected from 1932-2005. This extensive data set was then analyzed to examine the relationships between the sediment-dwelling invertebrates (i.e., benthos, benthic infauna), and sediment and water quality parameters in Hood Canal.

Goals and Objectives

The overall goal of this project was to evaluate the nature and degree of adverse effects, if any, to the resident benthos of Hood Canal as affected by low dissolved oxygen. The technical objectives included:

• Determine how the benthos of Hood Canal are distributed throughout the canal and how this distribution changes over time.
  
  
• Determine the patterns of bottom water DO levels throughout the canal and how this distribution has changed over time.
  
  
• Determine the relationship between indices of benthic community composition and the concentrations of bottom water DO.
  
  
• Determine which species, taxonomic groups, and benthic indices are most affected in Hood Canal and are, therefore, most important indicators of losses in benthic resources.
  
  
• Compare the benthos/DO relationships with those for other natural variables such as sediment texture, depth, and organic carbon content, and anthropogenic variables including chemical contamination and toxicity, to determine which relationships appear to be most important to the benthos.
  
  
• Identify the DO concentrations associated with the losses of important individual benthic species, sensitive taxonomic groups, and major phyla from the benthic communities.
  
  
• Develop an index for assessing the change in benthic community structure that can be attributed to variation in DO.

Findings

Analysis of available Hood Canal sediment quality, DO, and benthic infauna data suggests the following:

• Generally, chemical contamination and toxicity levels were low and confined to Port Ludlow, Port Gamble, and Dabob Bay. These factors appeared to have a very limited influence on benthic community structure in Hood Canal.
  
  
• Water quality data showed a steady decline over time in DO content and an increase in the area affected by low DO, especially in southern Hood Canal.
  
  
• In all but a few northern locations, benthic infaunal communities in Hood Canal generally were less abundant and diverse than communities found in other parts of Puget Sound.
  
  
• Nine unique benthic communities were distinguished throughout Hood Canal, adapted to the particular sediment and DO characteristics found in each area.
  
  
• The total number and variety of benthic infauna declined, and several stress-tolerant invertebrate species became dominant, from north to south along the canal’s main axis.
  
  
• Benthic communities changed as: (1) sediment texture became finer-grained (that is, as silt-clay content increased), (2) DO levels near the bottom decreased, (3) nutrient content (measured as percent total organic carbon) in the sediments increased, and (4) depth increased.
  
  
• Noticeable changes in community structure occurred as DO levels decreased from >10 mg/L to >3-6 mg/L and then to <1 mg/L. Various benthic infauna responded differently, with either increased or decreased abundance, to changes in the range of near-bottom DO levels.
  
  
• Further analysis indicated that there was little change in northern Hood Canal benthic infauna that could be attributed to declining oxygen levels. However, between 1991 and 1999, changes in benthic community structure at a location near the Great Bend were consistent with declining DO concentrations.

Results suggest that sediment-dwelling invertebrates were likely to be sensitive to natural and human-caused changes to sediment grain size and organic content, as well as to levels of DO in bottom waters of Hood Canal. The full report describes initial steps to develop critical DO thresholds which can be used to determine when benthic infauna are at risk. Additional information and research needed to develop better thresholds are also identified.

Publications

Data

Hood Canal water column and sediment data supplement.