Areas Indicating or Susceptible to Eutrophication

Presented in the attached graphic is a compilation of the Marine Waters Monitoring (MWM) data showing station locations where eutrophication is indicated and areas that are susceptible to eutrophication. This summary graphic compiles five water quality indicators that we measure: degree of density stratification; high fecal coliform bacteria concentration; high ammonium concentration; consecutive months of below limit nitrate; and low dissolved oxygen (DO). This graphic presents the best compilation of known problem areas and areas of susceptibility with respect to eutrophication in marine waters.

Eutrophication, the external addition of nutrients to a system, can lead to environmental problems such as low dissolved oxygen, noxious algal blooms, and fish kills. Thus we use low DO as an end-point measurement of where eutrophication may have occurred. On the attached graphic, the MWM stations in Puget Sound that have low DO are shown by red (<3 mg/L = near-hypoxia) and yellow (<5 mg/L = biological stress) dots.

To assess susceptibility, we use the additional indicators stated above. Eutrophication-susceptible areas are those that are permanently stratified, that indicate natural nutrient-limitation, and/or that show evidence of anthropogenic contributions (high fecal coliform or ammonium concentrations). The MWM stations in Puget Sound that indicate susceptibility to eutrophication are shown in pink.

The graphic is a compilation of WY 1990-1995 data. Not all stations were monitored in all years, so classification was based on the occurrence of a condition in one or more years. Prior to WY 1990, data is not comparable due to refinements and changes in analytical and sampling techniques.

Results

In all, 71% of the stations monitored (29 out of 41) show either low DO concentrations or susceptibility to eutrophication.
Of the 41 stations in Puget Sound, 15% show hypoxia (red) and another 20% have DO at biological stress concentrations at some point throughout the year. Some of these stations have naturally occurring low DO, but it is strongly probable that, especially at all of the stations with red dots, humans are exacerbating the problem by adding nutrients.
The stations that show susceptibility (36%) are areas where nutrient inputs should be carefully planned for and controlled since additions will result in increased primary production with the potential for low DO concentrations to develop. Most of the susceptibility is in South Puget Sound and Kitsap Peninsula, with implications for human population growth and development in these areas.

MWM stations in Grays Harbor and Willapa Bay do not show low DO concentrations, but both show susceptibility.

El Niño impact on Puget Sound temperature and salinity (14-Apr-1998)

For the previous moderate El Niño event (1992-91), data from the Washington State Dept. of Ecology's Marine Waters Monitoring program showed that Puget Sound surface seawater temperature and salinity were warmer and saltier, respectively. The influence of warmer and drier local weather during that time likely played a large role in this signal. The data and analysis can be viewed in Newton (1995), available from the Puget Sound Water Quality Action Team's Puget Sound Research Conference '95 Proceedings.

Monitoring data for the 1997-98 El Niño event are still being verified and analyzed. However, early indications are that warmer than average sea surface temperatures were observed during this winter (Dec `97-Feb `98). The surface salinity signal is less clear. Salinities were exceptionally fresher throughout 1997 due to streamflows well above normal (~150% of mean, see USGS data). Lately, however, salinities have been approaching average values.

Source:
Newton, J.A. 1995. Observations of El Niño weather conditions reflected in the temperatures and salinities of Puget Sound monitoring stations. In Puget Sound Research '95 Proceedings, 2: 979-991.