SENIOR RESEARCH PROJECTS FOR 1996
ABSTRACTS OF FINAL REPORTS
School of Oceanography, University of Washington
Nontechnical Summary. Terminal 108 was restored to a wetland by the Port of Seattle in 1987 as mitigation for the development of Terminal 30. The primary goal of the restoration was to improve habitat for fauna commonly preyed upon by juvenile salmonids. A long term monitoring plan was designed for the restoration project, including assessments focused on epibenthic taxa, organisms associated with the sediment surface. This study represents an analysis of intertidal epibenthic fauna nearly ten years after the completion of the habitat restoration. Under the assumption that the control of the 1996 study is representative of the pre-construction assemblage, some comparisons may be drawn between the study and the control. The population of one target taxa for the 1996 assessment was more evenly distributed across the study transect than the control, suggesting even substrate distribution in the study transect. Fauna abundance of most target taxa declined as a result of the habitat restoration. The most likely cause of these decreases were incomparable sampling techniques and insufficient replicate sampling. Cores were used in the pre-construction assessment, and suction pumps were used in the 1990 and 1996 studies. To detect real differences between sites using the suction pump, at least twenty-five replicates should be taken at the same tidal height for each transect. Cores are more effective, requiring a minimum of six samples to obtain reliable results. In the previous studies, no more than three replicates were taken at any given tidal height, and in many cases only one data point represented each tidal height. It is thus determined that a very specific protocol should be adhered to when monitoring wetland or intertidal ecosystems.
Abstract. Terminal 108 was restored to a wetland by the Port of Seattle in 1987 as mitigation for the development of Terminal 30. Assessments of epibenthic juvenile salmonid prey taxa, were conducted in a long term monitoring plan of the restoration project. This study represents an analysis of intertidal epibenthic fauna ten years after habitat restoration completion. Abundance of most target species has declined since the wetland construction. Gammarid amphipod populations for the 1996 assessment were more evenly distributed across the study transect than are the control, suggesting substrate differences alteration resulting from habitat restoration. The cores used in the first study were more effective than the suction pumps used in subsequent studies, sacrificing confidence in data comparisons. The declines were probably artifacts of inadequate consistency in sampling between sampling years. Thus, a very specific and well-tested protocol should be adhered to when monitoring the intertidal epibenthic fauna of the Diagonal Way restoration site.
A synopsis of the report, including the figures, is available on line.
Nontechnical Summary. This project attempts to find out where the copepod Eurytemora americana, a planktonic crustacean, lives within the Duwamish River estuary. Finding where these copepods reside may give an indication of how they are able to stay within the estuary without getting flushed out by the river. Possible means of staying within the estuary are moving up and down to ride the opposite flowing currents, upstream at depth and downstream in the upper layers of the river; repopulating quickly; or just clinging to the bottom sediments. To know where it is, E. americana may use physical signals such as current flow or salinity and move to areas where these signals are appropriate. In addition to finding out how this copepod stays in the estuary, finding out where the copepod lives will help other researchers in possible future studies of the ecosystem. Other studies may involve the transfer of pollutants up the food chain, more retention mechanisms, and competition between zooplankton species. Water samples were taken with a pump and filtered through a 100 m mesh to catch the animals. This sampling was done at various spots in the river and at different depths and salinity levels in the water. Adult female copepods were counted to determine the relative densities of copepods in each water sample. The highest densities were found 7.5 km upstream from the mouth of the west waterway, chiefly in the marine layer.
Abstract. The spatial distribution of Eurytemora americana in the Duwamish River estuary was investigated in April, 1996. The copepod occurred chiefly in the marine layer (S>25 PSU) and was most abundant 7.5 km upriver from the mouth of the west waterway (7.5 Rkm). The population diminished upstream to the toe of the salt wedge (10 Rkm) where the extent of the marine layer ended; downstream, the population diminished at 3.6 Rkm, where competition with marine copepods may control the zooplankton assemblage (3.6 Rkm). Although the existence of a permanent marine layer in the Duwamish River allows E. americana to persist, other mechanisms such as vertical migration on a tidal cycle scale or migrational movements toward physical cues may also be used for retention.
The complete report is available online.
Nontechnical Summary. A shallow rise called a sill is located in the East Waterway of the Duwamish River. The sill plays an imporatnt role in the flow of the Duwamish River. The Duwamish River forks into the East and West waterways, but only the East Waterway has a shallow sill that constrains the river flow through it to approximately 20% of the total river flow. A distinct two-layer circulation is present at the sill, with a shallow fresh water layer lying over a marine layer called a salt wedge. As the tide changes the level and currents of water over the sill, the river outflow is dramatically affected. During an incoming flood tide, the salt wedge is moving upstream in the river. The currents associated with the flood tide effectively stop the Duwamish River surface outflow in the East Waterway, and thus, the majority of the outflow occurs in the West Waterway. Outflow in the East Waterway is limited to a period during the ebb tide from when the tide is at or near high slack to the beginning of flood tide, before the incoming currents achieve considerable strength.
Abstract. The flow of the Duwamish River is split into an 80%/20% regime between the West and East waterways, respectively. The presence of a sill in the East Waterway controls the volume of Duwamish mixed-water traveling through the East Waterway during the diurnal tidal cycle. Highest East Waterway water transport (9-15 cubic meters/second) occurred during periods at or near slack tides. Lowest water transport occurred during a period from two to three hours after the 0439 high tide. Outflow in the East Waterway does not occur during the flood tide periods. Five stations on an hourly cross-sectional transit of the East Waterway yielded CTD and current meter profiles of the two-layer system present in the waterway. A 0.3 m-1.2 m-thick 12-18 PSU mixed-water layer exits over the Puget Sound tidal wedge at 25-27 PSU. During a high tide of 3.4 m (11.2 ft), the water column height over the sill was 5-6 m, depending on station bathymetry. The highest average current velocities measured, ~60 cm/s, were at a locally deep channel during mid-ebb tide. The ~30 cm/s flood tide currents prevent seaward mixed-water flow, and ~20 cm/s ebb tide currents enhance the volume of mixed-water outflow when close to slack tide. At low tide of 0.25 m (0.8 ft) a two-meter water column existed over the sill. Tidal wedge velocities remained below 10 cm/s during low tide, while mixed-layer velocities averaged ~50 cm/s.
Nontechnical Summary. This paper reports new evidence for uplift along the Seattle Fault at the mouth of the Duwamish River 4 km southwest of metropolitan Seattle, Washington. Previous studies show that a large earthquake between 500 and 1700 years ago raised marine landforms at Restoration Point and Alki Points, 11 km and 7 km west of Seattle, respectively. A 1854 U.S. Coast Survey map of the west bank of the Duwamish River depicts forested upland platforms directly adjacent to the waterway with no intermediate saltwater marsh unit. The absence of a saltwater marsh unit suggests that the tide flat was suddenly raised above the reach of the tidal influence. One-inch cores were obtained from the platform to determine the subsurface stratigraphy. The study area was surveyed to establish vertical control and to determine the height of the upper boundary of the tidal deposit above mean lower low water. The mud unit, deposited in a subtidal to intertidal environment, contains some very fine-grained sand, clam shells and plant material suitable for age dating. Survey results show that a mud layer is 4.2 m above mean lower low water, about 1 m above modern high tide. This evidence suggests that the Duwamish River valley was tectonically uplifted. Based on other evidence for this event at Restoration Point and a comparative survey of the adjacent east Duwamish River bank, it is determined that a likely range of uplift was between 1.1 and 7 m. Plant material from the deposit yields a radiocarbon age of 1890 +/- 70 14C yr B.P.. This age correlate to a maximum time of uplift between 1685 and 1970 calendrical years ago. The minimum time of uplift, 1330 +/- 190 14C yr B.P., is based on radiocarbon dates by archaeological investigators of cultural material recovered from the sand unit above the mud deposit. These dates agree with the findings of other researchers who have determined the time of uplift along the Seattle Fault to be between 500 and 1700 years ago. This study extends evidence for prehistoric earthquakes in the Seattle-Puget Sound region 10 km east of that previously documented at Restoration Point.
Abstract. This paper reports new evidence for uplift along the Seattle Fault at the mouth of the Duwamish River 4 km southwest of metropolitan Seattle, Washington. This uplift may have coincided with the same earthquake that raised marine terraces at Restoration and Alki Points 11 and 7 km west of Seattle, respectively. An 1854 U.S. Coast Survey map suggests one or more marine terraces are present on the floor of the Duwamish Valley. Hand auger cores were drilled in the terrace to identify the depth of the relict tidal deposit. A survey was conducted to establish vertical control and to determine the elevation of the terrace above mean lower low water. The tide deposit is an olive green/gray, very fine sandy clay with some bivalve shells and plant material suitable for radiocarbon dating. No fossil flora in growth position was recovered. The results show that the elevation of the subsurface tidal deposit is at least 4.2 m above mean lower low water if the deposit formed in a subtidal environment or if compaction did not occur during shaking. Radiocarbon ages on preserved plant material in the tidal deposit show that the maximum age of uplift was 1890 +/- 70 14C yr B.P.. A minimum age of uplift, 1330 +/- 190 14C yr B.P., is based on archaeological material recovered from the site by other investigators. This study extends the known rupture length along the Seattle Fault 10 km east of Restoration Point. Possible variance in offset along strike of the Seattle Fault would produce important differences in energy release and ground motion that should be taken into account during preparation of alternative seismic zonation maps of the Seattle-Puget Sound region.
Nontechnical Summary. Ferry traffic is a regular feature of Elliott Bay. As the ferries move through the water, they cause disturbances that trail behind the ferry, spreading as the distance from the ferry increases. This disturbance will increase the mixing of water masses circulating in Elliott Bay. As the individual ferry wake effect is determined, it can then be multiplied by the number of ferry crossings each day, calculating a relationship between the mixing of the surface layer caused by the ferries and the surface mixing caused by natural processes.
Abstract. A volume was calculated that represented an estimate of the amount of water mixed by ferries as they crossed Elliott Bay. The volume consisted of the length of the ferry track across the bay, 4000 meters, the width of a ferry, 24 meters, and a depth of 3 meters. These are all conservative estimates (the length of the ferry track across the bay is known) of a disturbance zone caused by passage of a ferry, and determined by CTD profiles of temperature and salinity. This figure, 28,800 m3, was then compared to surface layer volumes for Elliott Bay as a whole, ranging from 0.5 meter depth (10 x 166m3) to 3.0 meter depth (65 x 106m3). The amount of mixing by the ferry traffic is higher than expected, indicating a need for further study on the ferry mixing effect on other surface-trapped phenomena.
Nontechnical Summary. Diagonal Way, a small embayment in the Duwamish River, Washington, is one of MetroUs future sediment cleanup sites: the sediments are so contaminated they either need to be dredged (i.e., dug up and completely removed from the system), or a sediment cap will be needed (i.e., cover the sediments with a layer of clean sediments). In order to determine the best cleanup method, it is important to know whether the sediments are subject to erosion. If so, a sediment cap made up of an inappropriate type of sediment may be quickly washed away. In this study, water velocity above the river bed at a particular location was monitored and used to determine if erosion could be occurring. Using a calculation based on observations from past research on the topic, we determined that erosion was likely during the monitoring of this project. When a high velocity current arrives and erosion does occur, it is expected that more sediment will be in the water above the river bed. Measured velocities are thus compared with measured sediment concentrations in the water above the river bed to determine if they are related. No trend that would indicate the occurrence of sediment erosion was observed. The results of this study are thus inconclusive. It is recommended that a small cap of sediment be laid down at the Diagonal Way site to observe how it reacts to the environment.
Abstract. This study of the flow and hydrographic characteristics at the Diagonal Way cleanup site in the Duwamish River, Washington, provides background for determining the best sediment remediation method for a coming cleanup project by Metro/City of Seattle. Vertical profiles throughout the cleanup site were collected using a CTD, transmissometer, and current meter. The typical salt wedge estuary pattern of a surface fresh water layer (salinities as low as 7 psu) and bottom marine layer (salinities up to 28.5 psu) was observed. As expected for an estuary of this type, the fresh water and marine water layers had relatively low suspended sediment concentrations ( ~20 mg/l and ~5 mg/l, respectively), while the interface between the two layers had a relatively high suspended sediment concentration (up to 60 mg/l). An 11-hour time series was collected using an instrumented tripod system which included a CTD, transmissometer, and current meter, all set to sample at a height of 50 cm above the river bottom. Based on an empirical curve that relates sediment size to the minimum velocity required for erosion of that sediment, it was estimated that at the location of the tripod, velocities over 16 cm/sec would tend to cause erosion. Measured velocities at the tripod location reached over 30 cm/sec and were often higher than 16 cm/sec, indicating a tendency for erosion. A low correlation of velocity with suspended sediment concentrations provided no evidence for the expected erosional events. Due to the inconclusive nature of this study, it is recommended that a small test sediment cap be laid at the Diagonal Way site to determine its effectiveness in this highly variable estuarine system.
Nontechnical Summary. The Duwamish River Estuary is of the salt wedge type: it is composed of a fresh surface layer and a saline lower layer. Most salt wedge estuaries experience very little mixing between the two layers. The mixing is constant along the salt wedge and with the tidal cycle. The Duwamish River Estuary, however, may be the site of more intense mixing than general models of salt wedges assume. Evidence was found that supports the presence of periodic 'intense mixing events' near the furthest extent of salt water intrusion into the estuary. This location coincides with the upriver extent of dredging. Temperature and salinity measurements showed that a pool of cold water moved down river from this site. The pool of water may have been formed by an intense mixing event. However, measurements were not taken before or during the formation of the cold pool, so little was learned about the forces that caused it. The measurements did reveal that other processes are important in the estuary. The surface one-half meter of the estuary was heated by the sun and increased in temperature by 2.3 0C. The tidal movement of water back and forth in the deeper part of the estuary was also observed.
Abstract. To study previously observed 'intense mixing events,' salinity and temperature measurements were taken over most of a tidal cycle at the toe of the salt wedge in the Duwamish River Estuary. The mixing events may be the major source of movement of water from the deep, saline layer into the surface layer. Contour maps produced from the measurements support the existence of a mixing event. A pool of low temperature water, surmised to have been created by a mixing event, was observed to travel down the river. Mechanisms involved in creating the pool of low temperature water remain unclear. Surface solar heating and tidal movement were found to be other important processes in the estuary.
Nontechnical summary. This study shows that turbidity currents are major mechanisms for transporting sediment from a small, primarily depositional, marine bay. Submarine turbidity currents are density-driven flows, similar to subaerial powder-snow avalanches. Sound-waves were used to locate deposits within Elliott Bay, from which the velocities and sediment transport capabilities of the turbidity currents were reconstructed. Examination of sediment samples taken from the bay revealed that turbidity currents occur approximately every 100 years. Old charts were used to show that the eastern side of the bay is being eroded, while material is being deposited on the western side. Because the velocities and sediment transport capabilities of these currents are substantial, care should be taken when choosing locations for piers, sewer outfalls, submarine cables, and dredge-spoil disposal sites.
Abstract. This study shows that turbidity currents are major mechanisms for transporting sediment from a small, primarily depositional, marine bay. Seismic reflection profiling and piston coring were used to estimate turbidity current velocities of 3 - 13 m/s, fluxes of 300 - 1900 cubic meters per second, and sediment transport capabilities of 280,000 cubic meters per event. Paleobathymetric analysis identified the eastern marginal slopes of the bay as undergoing continual erosion, while the western slopes were depostional. The prevalence and magnitude of turbidity currents suggest that care should be taken when choosing locations for piers, sewer outfalls, submarine cables, and dredge-spoil disposal sites.
Nontechnical Summary. Copepods are small crustaceans that live in both marine and fresh water regions. If exposed to trace metals, these animals can potentially ingest and store these contaminants in their bodies, and transfer them up the food chain. Little information is known about the marine copepods found in the Duwamish River Estuary, and these copepods have never been analyzed for trace metals. To determine what the copepods in the estuary are exposed to, this research focused on trace metal concentrations in two species of copepods which live in the Duwamish River Estuary. Eurytemora americana maintains an abundant population in the estuary and Pseudocalanus spp. inhabits the estuary, Elliott Bay, and the Main Basin of Puget Sound. Samples of copepods were taken from these locations and they were analyzed for the following trace metals: arsenic, cadmium, chromium, copper, lead, nickel, silver, mercury, zinc, and tin. Copper concentration was the highest in the copepods and mercury concentration was the lowest. In general, Pseudocalanus spp. had higher concentrations of the trace metals than Eurytemora americana. The detection of metal concentrations in these copepods indicates that these animals are potential transport agents of these contaminants out of the estuary and into the Main Basin of Puget Sound.
Abstract. Concentrations of As, Cd, Cr, Cu, Pb, Ni, Ag, Hg, Zn, and Sn were determined in two species of copepods, Eurytemora americana and Pseudocalanus spp. collected from 6 stations located in the Duwamish River Estuary, Elliott Bay, and the Main Basin of Puget Sound using Inductively Coupled Plasma Mass Spectrometry. Cu concentration was the highest, reaching 25 ppm dry weight in P. spp. and 5 ppm dry weight in E. americana. Hg concentration was lowest ranging from 0.002 to 0.008 ppm dry weight. In general, P. spp. had a higher concentration of metals than E. americana. The concentrations of all of the metals, except for Zn, Cd, and Hg, were comparable with documented values. Due to the fact copepods retained trace metals, they become potential transport agents of metals out of the Duwamish River Estuary and up the food chain.
Nontechnical Summary. The sea surface layer (SSL) is the interface between the atmosphere and the sea. It is approximately 1 mm thick and is home to many of the sea's tiny plants and animals (plankton), but many pollutants, such as oil, float in the SSL and can have harmful effects on the plankton living in the SSL. Dissolved metals, such as lead from burning leaded gasoline, also float in the SSL. In this study, SSL samples were collected and analyzed for plankton abundance and dissolved metal concentrations to see if a correlation existed between the amount of dissolved metals and the amount of plankton. Water samples were collected at a pristine (Sequim Bay) and a polluted (Elliott Bay) site in Washington State. Analysis of samples showed that metals and plankton did not enrich the SSL relative to 10 cm depth, except animal plankton from Sequim Bay which did enrich the SSL. Sequim Bay was enriched with plankton relative to Elliott Bay; however the metal concentrations were greater in Sequim Bay as well. This implies that there is not a correlation between dissolved metal concentrations and the abundance of plankton in the SSL or at 10 cm depth.
Abstract. The sea surface layer (SSL) is often a site of increased biomass (bacteria, phytoplankton, and zooplankton) relative to the rest of the water column. The SSL is also known to concentrate dissolved trace metals, which can concentrate in the tissues of some zooplankton and have negative effects on growth and reproduction. In this study, dissolved trace metal concentrations and the biota of the SSL were estimated in an industrialized bay (Elliott Bay) and a pristine bay (Sequim Bay) in Washington state to determine if a correlation between biota and dissolved trace metals existed. While the SSL samples collected showed no enrichment of bacteria, chl-a, or metals in the SSL relative to 10 cm depth samples in either bay, the pristine bay samples showed enrichment compared to the industrialized bay. However, the pristine bay also had higher concentrations of dissolved trace metals than the polluted bay; implying there is not a negative correlation between dissolved trace metal concentrations and the biota of the SSL.
Nontechnical Summary. Many different pollutants find their way into the Duwamish River estuary, and Metro's combined sewer overflows ( CSO ) is one source of them. CSO contain toxicants or metals which are discharged into the estuary. It is crucial to know how the toxicants behave and where they eventually end up. In this study, the partitioning of iron in the Duwamish River estuary water column will be investigated. In the water column, iron exists in three forms: dissolved ( any particulate and dissolved iron that pass through a 0.45 mm filter ), colloidal ( dissolved and particulate iron that pass through a 1 mm filter ), and particulate ( dissolved iron and particles retained on a 0.45 mm filter ). When dissolved iron in river water mixes with seawater in the estuary, iron precipitates from dissolved to particulate. Particulate iron is mostly in its oxide phase, which has high surface area and adsorptive capacity. It is able to adsorb other metals onto its surface. Particulate iron in the water column can be reduced back to its dissolved form, get settled out on the sea floor, and/or get flushed out to the lower estuary or even further out to the Elliott Bay. This means that when particulate iron forms and toxicants in the sewer effluents adsorb to this iron oxide, the toxicants will either settle out to the seafloor or get flushed out of the estuary. Thus by determining which of the three forms dominate the existence of iron in the estuarine water column, we can determine the fate of toxicants.
Abstract. The partitioning of iron in the Duwamish River estuary water column is investigated by using a modified Ferrozine method to determine the amount of removal of iron by flocculation, which results from mixing of river water and sea water with increasing salinity. Flocculation of total iron concentration decreases with salinity. Maximum removal of iron occurred after salinity reached ~ 4 o/oo. There is a greater amount of particulate iron than dissolved iron in the estuarine water column. Removal of iron is non-conservative and not biologically determined. Metal pollutants that find their way into the estuary will most likely be adsorbed to particulate iron and settle to the sediments and possibly increase sediment contamination.
Nontechnical Summary. Marine communities that live near highly populated shores, like those found along Elliott Bay, can become polluted from human sources. These pollutants are very dangerous to the marine environment, but they are difficult to clean up. One type of remediation effort is sediment capping, which is the process of applying clean sediment over a patch of highly polluted sediment. This capping process destroys all the animals that were living in that area, but the new clean sediment offers an ideal place for new organisms to settle and live. Determining how a new benthic community becomes established is important in order to assess if sediment capping is a good method of dealing with marine sediment pollution. Recolonization of the cap can be investigated by looking at the numbers and kinds of species living on the caps, by using measurements of community diversity, and by looking at how animals of different groups change in abundance over time. This study looked at two capped sites in Elliott Bay and inferred that the benthic communities were healthy and recolonizing as expected.
Abstract. Sediment capping is a relatively new pollution remediation effort that is done to isolate contaminants, thereby protecting and enhancing the resident benthic communities. Two such sites exist in Elliott Bay, the Denny Way cap and the Pier 53-55 cap. The effectiveness of this remediation effort was examined at both sites by inferring the health of the benthic communities from patterns of species succession, species diversity, occurrences of certain indicator organisms, and the number of species found on the caps. The caps appear to be producing the expected effects of protecting and enhancing the benthic communities. The need for a control site became immediately apparent, as did the need for continued monitoring of both sites on a long-term basis.
Nontechnical Summary. During the first week of April, 1996, four long sediment cores were taken from Elliott Bay, Puget Sound, Washington, two of which were analyzed for historical changes in mercury, silver, and lead concentrations. Core lb, from the central ridge in Elliott Bay, was chosen because the site was expected to be relatively undisturbed by slumping, shoreline construction, or any other human activity: as the sediment core consisted of uniform silty sand, it appeared to be undisturbed. Sediment accumulation rates could not be accurately calculated, however, because the activities of the radioactive isotope, 210Pb, were too low; thus, dates could not be assigned to depths in the core. Mercury, silver, and lead concentrations throughout the core did not exceed concentrations found in the sediments of the Main Basin of Puget Sound (MBPS), with the exception of mercury and lead in sediment 12 cm below the surface.
Core 2b, taken from down current of the Denny Way combined sewer overflow (CSO), which discharges highly contaminated effluent, was expected to detect a possible signature of the Denny Way CSO. But it was a highly disturbed core and sediment accumulation rates could not be calculated. Concentrations of mercury, silver, and lead throughout Core 2b did not exceed those found in the Main Basin of Puget Sound, suggesting that this particular site does not receive high levels of contaminants from Denny Way CSO, although a shallower site, closer to the shoreline, may.
Nontechnical Summary. Animals living in estuaries are exposed to rapid fluctuations in environmental conditions. The tide pushes salt water upriver and draws it out again on a daily basis, while the river feeds the estuary with a constant supply of freshwater. Marine organisms are significantly affected by relatively small changes in their environment, such as the amount of salt dissolved in the water they live in. Animals inhabiting estuaries may therefore have a tolerance for a wide range of salinities. Eurytemora americana is a copepod, or small crustacean (1.4 mm in length), found in the Duwamish River Estuary, Washington. A sample of these copepods was collected from the river in April, 1996, and exposed to different salinities in a laboratory experiment. The copepod's protein composition was studied for each salinity treatment to investigate the correlation between environmental stress and the production of new proteins in the copepod. Certain proteins have been found to help organisms recover from environmental stress. A separate laboratory experiment was carried out to determine if E. americana is particularly suited for a specific salinity. The latter experiment revealed that E. americana is capable of tolerating a wide range of salinities, but not fresh water Two new proteins were produced by the copepods when they were exposed to freshwater. The specific role of these proteins is unknown.
Nontechnical Summary. Dredge spoils (which are the sediments removed during a dredging operation) from the contaminated Duwamish riverbed were dumped at the Fourmile Rock disposal site in Elliott Bay from 1972 to 1987. The disposal site is located on a submarine slope that has experienced landslides approximately 3/4 of a mile (1.2 kilometers) to the northwest of the disposal site. This research investigated whether submarine landslides have been, or are likely to be in the future, a factor in the distribution of contaminated dredge spoils outside the disposal site. No evidence of past landslide activity nearer than 3/4 of a mile from the disposal site was found. A comparison of water depths in 1996 and in 1935 showed most of the dredge spoils remained where they were originally dumped. As the dredge spoils hit bottom during disposal, some of the dredge spoils may have slid down a small channel approximately 330 feet (100 meters) to the northwest of the disposal site. The channel might have transported contaminated sediment downslope to the south and the west of the disposal site. The channel shows indications of transporting sediments from the slope to deeper water prior to the start of disposal activities. The slope above the disposal site may show signs of creep, which is a slow movement downslope at a rate of a few inches per year. Creep has the potential to weaken the slope and increase the probability of a submarine landslide. A submarine landslide occurring at the disposal site would likely transport contaminated dredge spoils into the deeper waters of Puget Sound.
Nontechnical Summary. Mussels were collected from sites near downtown Seattle in the Duwamish River and Elliott Bay. Due to the industry and increased human population size in this area it is known as an urbanized area. Other sites, the non-urbanized sites, were chosen because of the lack of industry and small human populations. Comparison of the rates at which mussels grow showed that the mussels living in the urbanized sites grew at a slower rate than did the mussels living in the non-urbanized areas. The decrease in growth rates in the urban sites could define a link between pollutants more commonly associated with urban sites and the impaired growth rates of the mussels.
Abstract. Mussels, Mytilus edulis, collected from five urbanized sites in the Duwamish River estuary and Elliott Bay, WA, during the month of April, 1996, revealed stunted growth patterns relative to mussels collected from four non-urbanized sites in the surrounding Puget Sound, WA. Mussel age, determined by interpreting external growth bands on mussel valves, and mussel wet tissue weight were evaluated to suggest a link between high levels of anthropogenic contaminants and impaired mussel growth.
Nontechnical Summary. A total of 127 individuals from two populations of coho salmon (Oncorhynchus kisutch), sampled from two locations, were examined for variation in the nucleotides that constitute the mitchondrial DNA (mtDNA). Mitchondrial DNA is found in an autonomous, cytoplasmic organelle (the mitochondria) in each cell. It is maternally inherited and plays no role in the formation of proteins for extracellular transport. Populations were sampled from the Green River and Minter Creek watersheds, both located in the Puget Sound area of Washington State. Three different regions of the mtDNA were surveyed using polymerase chain reaction (PCR) and restriction enzymes. PCR allows for the exclusive amplification of certain regions of the DNA. Restriction enzymes cleave the amplified DNA at recognition sites; each enzyme recognizes a specific sequence of nucleotides and will cleave the DNA only at those sites. Two of the three surveyed regions showed variation at this level. Each variation was given a letter designation (either A or B) and the frequency of these designations was calculated for each of the populations. There was a statistically significant frequency difference between one Green River population and all other populations. These molecular markers may be useful in differentiating coho within the Puget Sound area and elsewhere in the range of coho.
Abstract. A total of 127 individuals from two different populations of coho salmon (Oncorhynchus kisutch), sampled from two different areas, were examined for mtDNA variation. Populations were sampled from the Green River and Minter Creek watersheds, both located in the Puget Sound area. The NADH dehydrogenase subunits five and six (ND5/ND6), subunits three and four (ND3/ND4) and the cytochrome b1/D-loop region of the mtDNA were examined using restriction fragment length analysis of products amplified by the polymerase chain reaction. Both the ND5/ND6 and the cytochrome b1/D-loop region showed variation at this level. Three haplotypes were detected using the restriction enzymes HaeIII, Sau96I, and BstNI. Haplotype frequencies were calculated for all five populations. There was a significant frequency difference between one Green River population and all other populations. The difference in haplotype frequency between the other populations was not statistically significant. These markers may be useful in differentiating coho within the Puget Sound area and elsewhere in the range of coho salmon.
Nontechnical Summary. Sediment grain size distribution was determined at the Diagonal Way cleanup site in the Duwamish River, Washington. Surface sediment samples were collected at the site and analyzed for contaminants by Metro. This area was of interest due to high sediment contamination levels centered around two combined sewer overflows (CSO). Sediment grain size relative to sample location was used to describe how the sediments were deposited in the area. The type of deposition that a particular location is subjected to provides useful information when considering different methods of treating the contaminated sediments. The results of the sediment grain size distribution showed that there were two distinct types of deposition occurring in the Diagonal Way area. One of the areas being considered for treatment is located within a sediment region that is susceptible to further deposition by particles brought in by the water column. The implications of this type of deposition are that once the contaminated sediments are contained, perhaps by a cap of clean sediment, further contamination could occur by contaminated particles from elsewhere in the river being deposited on top of the clean cap.
Abstract. The sediment dynamics at the Diagonal Way CSO cleanup site were analyzed to provide information on the depositional environment. Surface sediment grabs were taken from forty-two sample locations throughout the area. The sediment size distribution was analyzed utilizing the Passega method which separated the sample locations into two areas, each with a distinct type of sediment. In one area, the sediment was deposited by rolling transport, and in the other, it was deposited by suspended transport.
Nontechnical summary. How the change from fresh to salt water in a river estuary affects whether toxic metals remain dissolved in the water or become attached to particles is the question addressed by this study. Lead is the toxic metal examined. This study found that approximately the same levels of lead were in the river as detected by previous studies, and that most of the lead present was attached to relatively large particles. The ratio of lead attached to particles to lead dissolved in the water is known as the partition coefficient. As the river water became saltier (increased in salinity), more and more lead became attached to particles instead of remaining dissolved, and so the partition coefficients increased. The part of the estuary where fresh and salt water first mix is called the null zone, and in this region the partition coefficients were probably affected by factors other than salinity. This study suggests that these other factors might include the relationship between the sizes of particles that lead attaches to and how fast lead attaches to particles in the null zone. The findings of this study could help estimate how far toxic metal pollution will extend past the river mouth, as well as where it can be expected to be most severe.
Abstract. The effect of salinity on the partitioning of lead was studied in the surface waters of a stratified salt wedge estuary. The total surface water concentrations of lead, silver, and cadmium – obtained by ICP-MS analysis -- were in accord with previous studies, and most of the lead present was bound to particles sized greater than 0.2um. Apparent partition coefficients for lead generally increased with increasing salinity, though coefficients obtained for sites in the null zone (turbidity maximum) showed variability. It is hypothesized that within the null zone, partitioning of lead is affected by the phase of scavenging species and/or the position of the kinetic equilibrium between scavenging/adsorption/flocculation reactions and recycling/desorption/resuspension reactions. These findings could help refine toxicant fate models currently under development, as well as suggest avenues for future research.
Nontechnical Summary. The objective of this study is to determine trace metal concentrations in Duwamish River sediments and to relate that concentration to the size and organic carbon concentration of the sediment. Since smaller grain sizes have a larger surface area to which metals can adsorb, metals may be concentrated in areas dominated by smaller grains. Metals may also adsorb to organic carbon associated with sediment surfaces. These processes are related because organic carbon concentration may be related to surface area as well. Small particles stay in suspension longer than large particles, and thus are more likely to be deposited in areas outside of the Duwamish River Estuary. Knowing the factors controlling the adsorption of metal onto sediments in the Duwamish River Estuary may explain why certain areas are more or less polluted than others, and the same ideas may be applied to other estuarine systems as well. The metal/size relationship will provide information to biologists studying animals that eat particles of certain sizes, and to physical oceanographers studying erosion and deposition.
Three surface sediment samples were collected and separated into sizes which correspond to sands, silts and clays. The samples were then treated with different solutions to remove metals associated with the surfaces. These solutions were measured for metal concentrations using Inductively Coupled Plasma-Mass Spectrometry, which measures concentrations of metals as a function of their weight. The sediment was also analyzed for total and organic (from living matter) carbon content.
The results of this study were in agreement with similar studies conducted in other rivers. There have been no other studies of this kind in the Duwamish River or Puget Sound. The concentrations of the metals studied increased as the grain size decreased. This indicates that smaller particles provide a larger surface to which metals can sorb. However, there was not a large percentage of small particle in the samples studied, which may mean that they are being transported out of the river. No relation was made between the organic carbon content of the sediment and the metal concentration, since it is very likely that the metals and carbon come from the same source (like dumping of waste).
Each sample analyzed had detectable metal concentrations; however the particles in each sample were different sizes. The metals were also concentrated in different sizes for each station. This means that there are different mechanisms controlling the manner in which metals stick to surfaces. However, it is difficult to make definite conclusions about the Duwamish River because it is such an altered system.
Abstract. Although levels of pollutants and trace metals are monitored in the Duwamish River, there has been no attempt to quantify the concentrations of trace metals as a function of grain size. In order to study the relationship between grain size and trace metal concentration in the Duwamish River Estuary, three surface sediment samples were collected, including a freshwater endmember and two marine endmembers. Sediments were wet sieved into fine and very fine sands (250-63 um), coarse silt (63-38 um), and hydrodynamically separated with split-flow thin (SPLITT) cell fractionation into coarse, medium, and fine silts (63-38, 38-17, 17-8 um) and clays (<3 um). Lead, silver, and cadmium were analyzed with Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) after a sequential extraction with 30% H2O2 to remove metals associated with the organic phase, and 2.2 N HNO3 to remove metals associated with other geochemical phases. Organic carbon content of the sediments was also measured; however since it may be coming from the same source as the metals analyzed, it is probably not related to the trace metal concentration. In general the metal concentration increased with decreasing grain size. The freshwater sample had a different sediment size distribution than the marine sample, so the size class most important in concentrating the trace metals varied spatially downriver.
Nontechnical Summary. Copepods are small (~ 1 mm) marine crustaceans that are usually thought to eat particles and phytoplankton, which are marine plants (smaller yet than the copepods), suspended in the water. People don't usually think of copepods as eating bacteria because the bacteria are too small for the copepods to catch. The potential for copepods to consume bacteria attached to particles has important implications in both trophic ecology and pollution control. The purpose of this experiment was to test whether certain copepods in the Duwamish River Estuary can feed on bacteria which cling to particles. This experiment compared the feeding rates of the copepods on water with a natural assemblage of bacteria, to feeding rates on filtered water, which only contained free-living bacteria. We did not find any difference in feeding on filtered water vs. water with large particles, and indeed found that there were not any particles large enough for the copepods to catch that had bacteria attached. We did, however, measure a small amount of feeding on bacteria in both types of water, but the feeding rate was not enough to sustain a copepod population. This suggests that the copepods are using some other food source (perhaps the marine plants) to live and grow.
Abstract. The potential for copepods to consume bacteria attached to particles has important implications for both trophic ecology of plankton and for pollution effects in estuaries. This experiment tested whether the estuarine, planktonic copepod, Eurytemora americana, could feed at appreciable rates on suspended particle-attached bacteria, but not on free-living bacteria. Clearance rates were determined by measuring uptake of the radioactive label, 3H thymidine, into both E. americana and bacteria in short incubation experiments. Copepods, followed by 3H thymidine, were released into a suspension of bacteria. After one hour, the amount of isotope in the copepods and bacteria was measured, which permitted the calculation of clearance rates by the copepods on the bacterial populations. Grazing on free-living versus particle-attached bacteria was measured using both a "natural" bacterial assemblage and an assemblage containing only free-living bacteria. The study showed that there were no detectable bacteria attached to large particles (>5 um), although there was a small but measurable amount of feeding seen in both treatments by E. americana on bacteria. This feeding was not enough, however, to sustain the copepod population. This suggests that the E. americana in the Duwamish River Estuary is using some alternate source of nutrition, perhaps phytoplankton.
Nontechnical Summary. A computer model that simulates physical characteristics of the Duwamish River Estuary, located in Seattle, Washington, has been redesigned. The program is designed to use small sections in the estuary and simulate changes in the flow and concentrations in the water column due to tides, river flow, and observed data collected by the user. This report not only details how to run the model, set up proper input files and error conditions, but also details the changes and corrections that have been made to Fischer's original model from 1965.
Abstract. A numerical model of the Duwamish River Estuary has been rewritten in ANSI C computer language. This model computes salinity, temperature, phytoplankton concentrations based on chlorophyll a, biochemical oxygen demand, dissolved oxygen concentrations, pH, total and fecal coliform, alkalinity, and total inorganic carbon concentrations. These concentrations are calculated using the conservation-of-volume equations and observed data. This report gives an outline of modifications to the original version and remaining tasks of translation. A user manual is included.
Nontechnical Summary. When fresh water from a river flows into a body of salt water, it tends to float on top and form a distinct layer (called a "plume") because it is less dense. Consequently, the upper four or five meters of Elliott Bay, Washington, contain partly fresh water and a lot of tiny grains of material from the Duwamish River. This material, called Suspended Particulate Matter, or SPM, is partly derived from rock and partly organic. Tiny animals that live in the water and consume organic material are called zooplankton. Some of them have elaborate filtering equipment with which they can capture particles smaller than 1/100th of a millimeter in diameter. Others can only catch larger particles (like each other). In this study, various parts of Elliott Bay were sampled in order to find out where and how big the particles were and where different types of zooplankton liked to be. As it turned out, most of the SPM was less than 1/100th of a millimeter in diameter, and it was indeed concentrated within the fresher water near the surface of the bay (within the river plume). One tadpole-like zooplankton species, called Oikopleura dioica, can catch grains of SPM by passing water through very fine filters. It apparently makes a living by eating the organic material off of them. Luckily for O. dioica, the particles are also too small to clog its other filters. O. dioica was found in large numbers in water from the Duwamish River plume and relatively small numbers in the deeper, saltier water (which also had fewer particles in it). On the other hand, an insect-like zooplankton species called Microcalanus was more common in the water outside of the river plume. It prefers to feed on tiny floating plants, called phytoplankton. Most of the SPM in the river plume was either the wrong material or the wrong size (too small) for Microcalanus to catch. Microcalanus apparently grows and reproduces more successfully in deeper or more open water, which accounts for its higher abundance there.
Nontechnical Summary. When coastal environments become densely populated, such as Puget Sound, WA, the potential for direct human impact on the marine environment is significantly enhanced. The Duwamish River, which flows into Puget Sound, is used as a sewage discharge conduit in times of excessive precipitation in Seattle. These discharges may increase the nutrient content of the estuary (from the river mouth to ~5km upriver) and have important effects on the biology and chemistry contained therein. Ammonia, a nutrient from which organisms acquire nitrogen for their metabolism, has been shown to be more variable than any of the other nutrients in the estuary. In order to determine if this variability is caused by biological or physical processes, samples of bacteria from the estuary were used in an experiment which estimates the bacterial portion of total ammonia uptake over time. The bacteria were separated into free-floating and particle-attached categories in order to more fully understand what impact the bacterial population might have on the nutrient. Also, photosynthesizing organisms, which use light and nutrients to synthesize food, were sampled to determine the magnitude of their abundance. The results of these experiments and measurements indicate that phytoplankton (photosynthesizers) and bacteria are not the main factors influencing the distribution of this nutrient in the estuary. Future study should focus on the physical circulation that occurs in the estuary as a function of river outflow, tides, and sewage discharges.
Abstract. Understanding the relationships between the biology and chemistry of estuarine systems is important when considering the potential effects of anthropogenic influence. Specifically, knowledge of how the biota of an estuary influence the nutrient regime is necessary for predicting the influence of nutrient enrichment (ex. sewage discharges). The Duwamish River estuary, Seattle, WA, is an area of industry, dredging, runoff, and sewage discharge. The consequences of these alterations of the natural environment are not fully understood. An earlier study in this estuary showed relatively enhanced variability of dissolved ammonia as compared to other nutrients. In order to determine the main factor(s) influencing this distribution, measurements of nutrients, salinity, chlorophyll a, and bacterial abundance and uptake (<3um and particle attached) were taken at a single station from high tide to high tide. Particle-attached bacteria were expected to have a significant influence on the distribution of dissolved ammonia in this system. Although particle-attached bacteria display faster rates of nutrient uptake than free-living (<3um) bacteria, the magnitude of these uptake rates were small enough to have a negligible effect on the distribution of dissolved ammonia. Phytoplankton were light inhibited in the zone of greatest ammonia variability, indicating that this influence on dissolved ammonia is also negligible. A qualitative relationship between the stage of the tide cycle and the change in dissolved ammonia concentration per unit time suggested that physical processes were the dominant factor influencing dissolved ammonia in the estuary.
mcmanus@ocean.washington.edu. Last modified: 12 June 1996.