The increasing presence, persistence, and distribution of low dissolved oxygen concentrations in Hood Canal during the 1990’s and the repetitive fish kills during 2002, 2003, and 2004 indicate that hypoxia (low oxygen conditions) may be increasing in Hood Canal. A historical comparison of the inventory of oxygen in the deep waters of the southern portion of Hood Canal (Dabob Bay to the Great Bend) calculated during 2004 was at an all time low, compared with similar data available from the 1950’s and 1960’s. We know that Hood Canal has a long track record of low oxygen conditions, even anoxia and fish kills, but the recent data, collected using the same techniques, show more severe and persistent conditions. We need to understand what is tipping the balance and whether it will persist.
As related in the Science Primer, the situation in Hood Canal is complex. There are several factors that could be driving the present situation. The HCDOP IAM study will assess and quantify these factors so that useful information can be relayed to policy makers and others considering potential corrective actions to try to alleviate the condition.
The low dissolved oxygen situation in Hood Canal may be affected by many factors, such as our climate, the ocean, river and other freshwater inputs, all of which affect the flushing of the canal. Slow flushing means the water can become stagnant, sealed off from the air and algae photosynthesis that replenish oxygen. The situation may also be affected by factors, such as climate, ocean inputs, river and freshwater loads, and human loads of nutrients and carbon, all of which affect how much algal growth and organic loading the canal has, which ultimately deteriorate and cause a drawdown in oxygen concentrations.
Scientists have put forth the following six possible causes for the lower dissolved oxygen concentrations in Hood Canal:
1) Changes in production or input of organic matter, due to naturally better growth conditions such as increased sunlight or other climate factors;
2) Changes in production or input of organic matter, due to naturally better growth conditions such as increased nutrient availability;
3) Changes in production or input of organic matter, due to human loading of nutrients or organic material;
4) Changes in ocean properties, such as seawater density that affects flushing of the Canal’s waters, oxygen concentration, or nutrients in the incoming ocean water;
5) Changes in river input or timing from natural causes (e.g., drought) or from human actions (e.g., diversion) that affect both flushing and mixing in the Canal.
6) Changes in weather conditions, such as wind direction and speed, which affect the flushing and/or oxygen concentration distribution.
There is supporting evidence for all of these hypotheses. All of them make sense, and likely all or many may be contributing to some extent. We need to know which of these are important for the current situation in Hood Canal.
The HCDOP-IAM study arose out of the need to know whether human activities, and which ones (e.g., nutrient and carbon loading from many sources, freshwater flow diversion, changes to the biota and habitat), are major causes for the pattern of increasing hypoxia and effects that we observed. This need pairs scientists with the capability to make a quantitative monitoring/modeling assessment with local, tribal, state, and federal decision makers through the HCDOP. The multi-year HCDOP-IAM study, begun in 2005, is primarily financed through federal funds secured by Congressman Norm Dicks. This study is administered by the Applied Physics Lab of the University of Washington, through a contract with the Navy. It is co-managed by APL-UW and the Hood Canal Salmon Enhancement Group. For more information on the study, check out IAM Study.
