More Studies Are Needed

Salmon Populations

Up until now much of the scientific research has focused on adverse health effects of pollution on organisms living in the Duwamish River and the impact on human consumption.  What is less understood are the effects of this transformation on a larger scale, such as populations of fish and ecosystem dynamics in the Puget Sound.  This is further complicated by other factors that help to determine population viability, such as commercial harvesting and global climate change.  Population modeling of English sole (a bottom dwelling fish) showed likely declines due to lowered reproductive success in three out of four Puget Sound populations (8).  While the negative impacts on resident fish and shellfish in the Duwamish River are relatively easy to model, the impacts on migratory species such as salmon are more difficult.  In one study Arkoosh et. al. demonstrate that salmon are not a reliable indicator of anthropogenic chemical pollution.  Food webs in near-shore marine environments are usually complex and the immediate effects of pollution or habitat degredation may be offset by a variety of factors.  This could possibly lead to the long term destabilization of salmon populations.  Twenty six salmon stocks in the western U.S. have been listed as threatened or endangered.  While urban pollution and watershed degradation are know to adversely effect salmon, more research is needed to determine the extent of this in the Puget Sound and identify possible solutions to the problem. 


Photo by Dave Bickford from http://powerlines.seattle.gov/2012/12/19/seattle-city-light-acquires-32-5-acres-of-salmon-habitat/

While the focus for the cleanup of the Duwamish River is on industrial contaminants and a buildup over time of other chemicals, there is more that needs to be researched about the anthropogenic impacts on this river.  Recent studies have pointed to runoff from roadways that enter the river through small urban streams as a major contributor to pollution.  Coho salmon that migrate through the Duwamish to spawn in Longfellow Creek have shown signs of neurological and respiratory disorders.  In 2001 a study showed that this lead to the death of 90% of the salmon before they could spawn (14).  A major contributor to this could be the fossil fuel byproduct polycyclic aromatic hydrocarbons (PAHs) that flow from the roadways into the river, which can be in high quantities during the first rainfall of the season.

 Other Species

The impact that the altering and pollution of the Duwamish River wetland system has had on other species such as birds, invertebrates and mammals is not well known.  Marine mammals such as otters can often ingest large amounts of pollution without knowing, causing serious health defects (15).  One case study observed 87 species of birds over a nine year span of observation around the Duwamish River (5).  Wetlands are often important areas for breeding and migration of many populations, and the loss of 98% of the historic wetlands in this area has surely caused problems for native wildlife.  There have been some recent attempts at restoration, with mixed success.  The case study mentioned above saw a greater increase in benthic invertebrate abundance in restored habitat, while also noticing a decrease in bird diversity corresponding to new construction at another site.  While studies illustrating the effects of pollution on resident fish in the Duwamish date back more than 30 years, the effects of this pollution on invertebrate and bird populations are not as well known.  It is becoming increasingly understood that wetlands provide important ecological benefits.  The Duwamish River Estuary has been modified so extensively and over such a long period of time that the full impacts of this are not known.    


Photo by Jason Love from http://www.geotimes.org/aug07/article.html?id=feature_wetland.html