Publication Summary

The Washington State Department of Ecology began this study to determine how nitrogen from a variety of sources affects dissolved oxygen in South Puget Sound. Portions of South Puget Sound do not meet Washington State water quality standards for dissolved oxygen.

The study includes collecting and analyzing data, developing hydrodynamic and water quality models, and assessing alternative management scenarios. This report summarizes nitrogen (nutrient) and related data collected from July 2006 through October 2007. The data were collected from 90 marine stations within South and Central Puget Sound, 29 wastewater treatment plants discharging directly to Puget Sound, and 39 rivers and streams.

The Washington State Department of Ecology began this study to determine how nitrogen from a variety of sources affects dissolved oxygen in South Puget Sound. Portions of South Puget Sound do not meet Washington State water quality standards for dissolved oxygen.

The study includes collecting and analyzing data, developing hydrodynamic and water quality models, and assessing alternative management scenarios. This report summarizes nitrogen (nutrient) and related data collected from July 2006 through October 2007. The data were collected from 90 marine stations within South and Central Puget Sound, 29 wastewater treatment plants (WWTPs) and industrial discharges directly to Puget Sound, and 39 rivers and streams.

Future reports will describe hydrodynamics, water quality model development, and alternative management scenarios. If the results show that human-related sources of nitrogen must be reduced to keep South Sound healthy, the final technical report will identify what reductions are needed.

Of the nutrient loads from the land surface, rivers and WWTPs are significant sources of dissolved inorganic nitrogen (DIN; the sum of ammonium and nitrate + nitrite). Nutrients recycled from sediments are an important influence and during late summer may release loads comparable to those from WWTPs and rivers. Other sources of nitrogen include atmospheric inputs which are small in comparison to watershed sources, and septic systems which are included in the watershed loads within the sites monitored.

Water circulation and velocity patterns are complex. Stratification was most intense in Budd, Carr, and Case Inlets, and Oakland Bay. Low near-bottom dissolved oxygen occurred in many parts of South Sound, including but not limited to Budd, Carr, and Case Inlets. DIN levels varied seasonally and spatially, and also reflected surface oxygen depletion associated with productivity. Chlorophyll levels were highest in shallow inlets as well as in north Pickering Passage and Oakland Bay.

Link to EIM data for User Study ID MROB0004