(©)Scott Anderson
This research sought to determine the ammonia contribution of phytoplankton lysis in the Snohomish River estuarine system. It examined the effects of salt stress and the amount of grazing in a freshwater population of phytoplankton when it is exposed to saltwater. Abiotic saltwater was added to a freshwater sample to simulate salinity changes to 7, 14, and 21 ppt, and secondary dilutions were done to determine growth rates and grazing at the various salinities. The phytoplankton experienced increased mortality at increased salinity, but the ammonia change was imperceptible due to high concentrations in the samples from the wastewater treatment plant. Terrestrial plant material in the freshwater sample interfered with the determination of growth and grazing rates, so that the rates were not determined with any confidence.
(©)Kerrie Brockett
The purpose of this study was to compare the biological oxygen demand (BOD) of the surface water and sediments, upstream and downstream of the Marysville Wastewater Treatment Plant in Steamboat Slough. The suspended particulate BOD was measured at two locations: at the slough-river junction and at the mouth of the slough. The sediment BOD in the slough was measured at four locations, two of which were where the water column BOD was measured. Oxygen in the water samples was measured by the Winkler method. Oxygen in the sediment samples was measured by two different oxygen electrodes. Suspended particulate BOD averaged 4.79 ml O2/m^2/hr near the wastewater treatment plant and 24.53 ml O2/m^2/hr near the river-slough junction. Sediment BOD, estimated with an Orion oxygen electrode, averaged 160.2064 ml O2/m^2/hr near the treatment plant, 136.741 ml O2/m^2/hr approximately one-third of the way up the slough, 163.1459 ml O2/m^2/hr approximately two-thirds of the way up the slough, and 124.0027 ml O2/m^2/hr at the river-slough junction. Sediment BOD, calculated with a polargraphic oxygen electrode at these four locations averaged 167.5781, 34.3144, 50.27589, and 78.3506 ml O2/m^2/hr, respectively. There were no significant differences in BOD between locations. Sediment BOD was about three times higher than water column BOD and may be an important cause of oxygen depletion in the slough.
(©)Mark Cook
Mixing occurs between the freshwater of the Snohomish River and the saltwater of the Puget Sound. A quantitative non-steady state box model depicts the volumetric transports in the salt wedge estuary. The portion of the river south of the Hole in the Dike is the location of the largest horizontal volumetric transports and the most vertical mixing.
(©)Tina O'Day-Dusek
In a salt wedge estuary, marine water enters tha river system under the influence of tides and freshwater outflow. The marine inflow brings marine organic carbon into the system. The 13C/12C ratio in the benthic bivalve species Macoma balthica was determined with a Carlo Erba CHN microanalyzer. The organic carbon consumed by the bivalves was mostly marine in origin. There is little influence of freshwater organic carbon on the nutrition of Macoma balthica within the estuary.
(©)Magaret Edie
The Snohomish River, carrying pollutants, marine organisms, and sediment, empties into the Puget Sound. This outflow of freshwater into the saline Puget Sound forms a plume. CTD data and current measurements were taken in Port Gardner on April 4 and 6, 1995, on the R.V. Barnes to observe changes in volume and location of the freshwater over a tidal cycle. The Snohomish River did not form a classic plume. Instead, Port Gardner became fresher with small fronts throughout the area. The freshwater spread to the northwest and then to the west, and the amount of freshwater increased to over four times its original volume as ebb tide progressed. The dilution with saline water of the freshwater, and any pollutants in it, as it traveled from the river mouth into Port Gardner increased from 30 to 50 percent during the falling tide.
(©)Michelle Greene
Historical hydrographic data for the Snohomish River prodelta region, together with detailed modern bathymetry, were used to locate regions of net deposition and erosion and to describe the major morphological changes that have taken place in the delta front and prodelta region between 1886 and the present. The delta front prograded approximately 150 m between 1886 and 1963. During this same time period, the deep basins within all three prodelta provinces were characterized by regional deposition. Erosional channels mapped within these basins were determined to be pathways for sediment transported off the delta and the Gedney Island shoal. Modern bathymetry collected in April 1995 suggests that erosional processes are now dominant in all three prodelta provinces. Changes in the sources and magnitudes of sediment supply due to human activities may have drastically altered the distribution mechanisms and sedimentary processes within the Snohomish River Estuary system during the last 100 years.
(©)Elizabeth S. Housel
Downstream distributions and diurnal changes of dissolved oxygen (DO), dissolved inorganic carbon (DIC), and DIC 13C/12C were measured on April 5-6, 1995, to compare the effects of water flow, photosynthesis, respiration, and gas exchange on DO levels in Steamboat Slough. Conservative DIC and DIC 13C/12C behavior indicated that mixing masked the biological effects during flow conditions at this time. A positive deviation from conservative expectations of DO with respect to salinity was observed, suggesting that both mixing and gas exchange influenced DO levels in the slough. A two-section box model was constructed to quantify hourly oxygen changes by river and tidal flow, gas exchange, and respiration. The results of the box model suggested that sediment oxygen demand significantly influenced DO levels. Given the uncertainties in the box model calculations, however, the results were not inconsistent with the observed trends that mixing and gas exchange controlled DO levels in the slough.
(©)Adrienne Huston
Past studies have shown that the quality of some water bodies in the Snohomish River Watershed has violated water use standards. Bacteria that are found in the intestinal tracts of certain warm-blooded species have been identified as pollutants. Four river stations and five slough stations in the Snohomish River and adjoining Steamboat Slough were surveyed for existing levels of bacteria. Levels of total coliforms, fecal coliforms, and fecal streptococci were significantly higher in the slough than in the river. Fecal coliform levels in both water bodies were much lower than water quality standards. The data suggest that Ebey Slough may be a source of fecal coliform contamination to Steamboat Slough.
(©)Kurt S. Maekawa
Bacteria use extracellular enzymes that hydrolyze particulate organic matter (POM) and dissolved organic matter (DOM) to the utilizable DOM for bacterial metabolism. In this study, the L-Leucine 7-Amido-4-Methyl-Coumarin substrate (MCA-leucine) was used to determine the bacterial extracellular enzyme activity in the salt wedge of the Snohomish River Estuary, Washington. Additional data on salinity, ammonia, DOC, and POC were taken to evaluate effects of environmental conditions on bacterial extracellular enzyme activity. The goal of this study was to test 1) whether the extracellular enzyme activity of bacteria is correlated with POC or DOC, and 2) whether high levels of extracellular activity can be a source of ammonium to the ammonium peak. Only one sample was obtained within the desired salinities of 9-to-18 ppt, and that sample had the highest levels of bacterial extracellular enzymes, ammonia, DOC, POC, and PON. Results from all samples showed the trend of increasing levels of ammonia and salinity with increasing levels of bacterial extracellular activity. These results suggest that heightened levels of POC, DOC, and ammonia may be correlated with the increased levels of bacterial extracellular activity.
(©)C. Andrew Martin
Seismic reflection and side-scan sonar data reveal erosional and depositional features of a submarine landslide that occurred along the northeastern shore of Possession Sound near Mukilteo. These features lie adjacent to a large subaerial landslide scar, involving 1.18x10^7 m^3 of material, affecting approximately 0.60 km^2 of coastline. A distributary channel system 700 m long trends northwest from the inshore region at a depth of 20 m to an offshore depositional area in 180 m of water. The morphology of the branching channel head lets it effectively intercept sediments being transported along the eastern littoral zone of Possession Sound. Turbidite deposits approximately 20 m thick partially fill this channel. The deep-water depositional lobe has a convex upper surface and is more than 1.2 km wide. A piston core collected from the turbidite deposit consists of sediment generally coarser than that in a core from the Snohomish River prodelta. Depositional patterns in the core from the slide deposit are consistent with those of turbidite deposition. Shear strength measurements in this core are highly variable, in contrast to the shear strength values in the prodelta core that increase uniformly with depth in the core. From an average Puget Sound depositional rate and the depth to a seismic-stratigraphic sequence in Possession Sound that correlates with the distal landslide deposits, the landslide was determined to have occurred approximately 1300 yBP. This age correlates well with documented past occurrences of tectonic activity in the Puget Sound region, suggesting a possible paleoseismic correlation. This evidence of a large-scale subaerial and submarine landslide suggests that mass wasting processes are an active, and important, mechanism for transporting sediment into the deep waters of Puget Sound.
(©)Lorien A. Menna
The purpose of this study was to determine whether phytoplankton lysis might occur in the salt-wedge of the Snohomish River Estuary and, if so, what quantity of ammonium would be produced as a result. Dilution experiments were performed in April (1995) in the laboratory, using water from both the Snohomish River and Port Gardner Bay. Four different salinities were targeted and the concentration of ammonium was measured in each. Growth rates decreased with decreasing salinity, while high ammonium concentrations were found at the lower salinities. It could not be concluded that the effects of salt stress on marine phytoplankton were the source of the high ammonium concentrations.
(©)Lara Miller
The 210Pb technique was used to determine modern sedimentation rates on the Snohomish River prodelta near Port Gardner Bay in northeastern Puget Sound, Washington. Three box cores were obtained, one from each of the three distinct morphological provinces of the prodelta. A box core from the modern (southern) province yielded a sediment accumulation rate of 13.4 mm/y. This rapid accumulation rate is likely due to the sediment supply from the nearby channelized portion of the Snohomish River and the protected nature of this province. The central province has a sediment accumulation rate of 2.0 mm/y; likely causes for this significantly lower rate are the exposure to winter storms, a reduced sediment supply, and constricting bathymetry (higher current velocities). The northern province is characterized by a sediment accumulation rate of 6.7 mm/y. This rate is higher than that in the central province owing to exposure of this province to the less severe summer storms, which produce a lower energy environment. It is lower that that in the modern (southern) province owing to a relatively smaller sediment supply from the sloughs into the northern province than from the main river channel into the modern province. Seismic reflection data show the thickness of recent sediment in the modern, central, and northern provinces to be 9 m, <5 m, and 6 m, respectively. These thicknesses corroborate the 210Pb results. The results of this study indicate that the prodelta is a highly dynamic feature, acting as an effective sink for particulate matter entering Puget Sound from the Snohomish River system.
(©)Ross Murray
The height and speed of propagation of the tidal wave in the Snohomish River estuary affect many river and human activities. River height measurements were made at six stations from 1.8 to 22.2 km above the river mouth between April 4 and 10, 1995. A harmonic analysis was performed to determine the amplitude and phase of a representative diurnal, representative semi-diurnal, and the M4 harmonic tidal constitutents. The diurnal and semi-diurnal amplitudes fall by less than one-half in the first 20 km of river length. The length of the tidal region is 29 km. Therefore the study area has a smaller amplitude change and lower friction than the river above the first 20 km. The M4 constituent increases slightly, indicating a small amount of distortion in the tidal wave. Propagation times could only be calculated for the first 7 km of river, a section that is dredged. The propagation time could be accurately modeled by the shallow water wave equation and the river flow except in low water. Low water propagation times were significantly longer than the model predicted.
(©)Mark Ortmeyer
Steamboat Slough is a part of the Snohomish River Estuary in Everett, Washington. It is subject to intertidal fluctuations of channel width, depth, water velocity, and water volume transport. It is being used for wastewater remediation for the city of Marysville. Current profiles, cross-sectional depth profiles, CTD casts, and measurements of channel width were taken at four stations along the slough at different tidal stages from April 3 to 5. Taken together, these sampling times provided data for one complete tidal cycle. Subsequently, flux calculations of water volume and salt during one idealized tidal cycle were used to determine the residence time of water within the slough. Two methods were used to determine the residence time. Method 1 used values of velocity, channel width, depth, and salinity, averaged over space and time, and then it applied them to a box model constructed between stations in the lower half of the slough. Method 2 performed no averaging, but used discrete data points over a similar but more spatially resolved box model. Both methods provided residence times on the order of 5 hours for the lower portion of the slough. In order for wastewater loading within the slough to remain benign to the resident biota, discharge must take place during ebb tide near the Interstate 5 freeway bridge.
(©)Tae Sung Park
The bottom sediment in Puget Sound near Everett, Washington, contains concentrations of a known carcinogen, beno(a)pyrene, [B(a)P]. The biodegradation rates of B(a)P by the local benthic bacterial assemblage were determined in the laboratory under aerobic and anaerobic conditions. A slurry mixture of 50/50 by volume was enriched with 4ug/ml of B(a)P. The degradation rates under the two conditions were determined with a spectrophotometer measuring at 365nm and 600nm. The results show a higher degradation rate under aerobic condition than under anaerobic condition. During the experiment, an unexpected bacterial bloom was observed in all the anaerobic samples. This may be due either to the addition of redox buffer cysteine to the anaerobic samples or to the bacteria growing on the B(a)P.
(©)Tammara L. Pierce
High concentrations of ammonium in the Snohomish River Estuary, Everett, Washington, were found to be caused by anthropogenic inputs. In contrast, natural biological activity, such as regeneration from bacteria or exchange from pore water at the sediment-water interface, may act as a sink or a source. Incubation experiments resulted in an average fifty percent decrease in ammonium. However, the rate of anthropogenic input is 10 times greater than the biological removal, negating the rate of uptake of ammonium. Due to insignificant correlation of salinity and ammonium at the four stations studied, the ion pairing of saltwater anions and ammonium ions may not be a means of diffusion from pore water into the water column.
(©)Mela Swapp
The Snohomish River Estuary is a tidally influenced system of channels that consist of the main channel of the Snohomish River and several sloughs. As part of a group study in the estuary and adjacent waters, this project determined the residence time of water in Steamboat Slough. Measurements of current, salinity, and temperature, as well as depth profiles, were taken over a three-day period during the first week in April 1995. These measurements were combined to approximate a single 12-hour tidal cycle. The average residence time in the upper slough was about 3.5 hours. Tidal influence in the lower portion of the slough was large. The residence time of water in the lower slough varied from 0.5 to 13 hours, depending on the stage of the tide.