Publication Summary

A seasonal monitoring project was conducted in Budd Inlet from March through October 1992. The project was to provide baseline data prior to the implementation by the Lacey, Olympia, Tumwater, Thurston County Waste Water Treatment Plant (LOTT) of nitrogen removal from the effluent that is released into inner Budd Inlet. LOTT began removing approximately 90% of the effluent nitrogen during spring 1994. To investigate the impact of this change on water quality, monitoring was conducted in 1992 through 1994 (present).

Budd Inlet is a semi-enclosed, partially mixed embayment located at the southernmost end of Puget Sound. Water quality problems in this embayment include eutrophication (nutrient enrichment and excessive phytoplankton growth) and low dissolved oxygen (D.O.) concentrations during summer and early fall. The low D.O. concentrations are partially due to persistent stratification and decay of organic matter. In order to better quantify the timing and extent of these problems, a seasonal monitoring project was conducted in Budd Inlet from March through October 1992. Additional impetus for the project was to provide baseline data prior to the implementation by the Lacey, Olympia, Tumwater, Thurston County Waste Water Treatment Plant (LOTT) of nitrogen removal from the effluent that is released into inner Budd Inlet. LOTT began removing approximately 90% of the effluent nitrogen during spring 1994. To investigate the impact of this change on water quality, monitoring was conducted in 1992 through 1994 (present). In 1992, surveys were conducted bi-weekly at up to 23 stations in Budd Inlet. One 52-hour tidal cycle survey was conducted during mid-July. Measured parameters included temperature, salinity, depth, D.O., dissolved nutrients (nitrite+nitrate-N, ammonium-N, and orthophosphate-P), Secchi disk depth, chlorophyll a (in situ fluorometry and discrete laboratory analyses), phaeopigment, transmissometry, and phytoplankton taxonomy.

Results indicated that stratification was primarily salinity driven, being strongest in the inner bay, and decreasing from the head to the mouth of Budd Inlet. Low D.O. concentrations (D.O. <5.0 mg/L) occurred from July through October at near-bottom depths predominantly in the west inner bay, and to a lesser extent in the east inner bay and along the east side of the central bay. Near-hypoxic D.O. concentrations (D.O. <3.0 mg/L) were observed during late August and early October at inner bay stations at near-bottom depths. Surface nitrite+nitrate-N concentrations fell below reporting limits (0.01 mg/L) in the central and outer bay during mid-May and from mid-June to mid-September. The highest nutrient concentrations (particularly ammonium-N) were recorded in the west inner bay near the primary LOTT outfall. Phytoplankton blooms (chlorophyll a >10 mg/L) occurred throughout the bay during March through October, however, the highest chlorophyll a concentrations were consistently in the central bay, and were found during July through September. Although phytoplankton concentrations were higher in the central bay than in the inner bay, higher nutrient levels were found in the inner bay. The lowest D.O. concentrations were also in the inner bay, not in the central bay, where phytoplankton concentrations were highest. Blooms of dinoflagellate species known to migrate vertically occurred during July and August at central and inner bay stations. Phytoplankton vertical migration was indicated by the chlorophyll a profiles taken during the mid-July tidal cycle survey at the central bay stations but not at the inner bay station. This migration may be linked to nutrient availability. Potentially harmful (e.g., to vertebrates including fish or humans) phytoplankton species (Pseudonitzschia pungens and Heterosigma carterae) were present at both central and inner bay stations at various times throughout the sampling season, though no reports of toxicity or fish kills occurred during this time.

Tidal stage and diel variation affected many water quality parameters. Dissolved oxygen concentrations were lower during low tide than during high tide and lower at night than during the day. Phytoplankton blooms were located further out in the bay at low tide than at high tide. The freshwater lens from the Deschutes River/Capitol Lake outlet extended further out in the bay at low tide than at high tide. In order to deconvolute tidal (25-h period) from diel (24-h period) influences, sampling should occur over longer continuous time periods such as weeks. Continuation of water quality monitoring should be made following implementation of nitrogen removal from the LOTT effluent, to document the effect of nutrient input to an estuary of this type. The effect of the current input is difficult to assess without measurement of rates of nitrogen input and removal due to processes such as advection, primary production and benthic interactions.