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Focused Studies - Sinclair and Dyes Inlets

A seasonal monitoring project was conducted from March through October 1992 in Sinclair and Dyes Inlet in order to better quantify the timing and extent of problems with euthrophication and low dissolved oxygen (DO) concentrations.  Measured parameters included temperature, salinity, depth, DO, dissolved nutrients, phaeopigment, light transmission, and phytoplankton taxonomy.

We found that low DO conditions do not appear to be problematic in either Sinclair or Dyes Inlets; however, Sinclair Inlet does exhibit isolated events of low DO concentrations.  Further water quality investigation of low DO conditions should focus on inner Sinclair Inlet, in the vicinity of Port Orchard.  At times, this portion of the inlet showed elevated ammonium-N and phytoplankton concentrations as well as low near-bottom DO concentrations. 

More frequent sampling at that location in the late-summer to early-fall period would be necessary to assess how sporadic low DO concentrations are and, thus, whether these observations represent a significant water quality problem.  Sampling of the benthic community in this area would be useful in determining impact of low DO concentration events on biota. 

Measured DO concentrations were different during low tide than during high tide in this study.  A near-bottom moored sensor, capable of recording hourly data, could be used to determine the magnitude, temporal extent and variability of low DO concentrations.   Monthly data available from the long-term monitoring stations SIN001 and DYE004 do not resolve short-lived changes in DO concentrations nor adequately reflect water quality conditions elsewhere in these inlets.