CICEET Progress Report for the period 9/01/01 through 3/01/02

Project Title: Developing and Applying A New In Situ Technology for the Investigation of Episodic Contaminant Transport Events within Estuaries
Principal Investigator(s): John W. King, Alfred K. Hanson, Christopher R. Kincaid, Elizabeth Lacey Laliberte, James G. Quinn

Accomplishments
Scheduled Tasks:

1. Conducted a series of undulating tows with the SubChem XZ-Profiler system in the fall to establish the chemical concentrations and gradients impacting the NEERs region of Narragansett Bay during the dry season. Concurrent cruises with an ADCP system were performed to monitor water mass movement.
2. Sediment trap, surface sediment and core collection.
3. Laboratory analysis of sediment, sediment trap and core material. Analyses included grain size, trace metal (cadmium, copper, lead, nickel and zinc), simultaneously extracted metal/acid volatile sulfide (SEM-AVS), nutrients (carbon and nitrogen) and organic contaminant concentrations (of sediment from selected core subsamples).

Progress on Tasks

1. Conducted field surveys with the SubChem XZ-Profiler system, on November 15 and 16, 2001, to map the dry season nutrient distributions during ebb tide. The nutrient data was merged with CTD and ADCP data in order to investigate the inter-relations of all observed parameters and estimate nutrient fluxes within the estuary.
2. Fieldwork in September and December 2001 to collect sediment samples and retrieve/deploy sediment traps and collect core.
3. After sample collection, bottom sediment was subsampled for grain size and trace metal analysis. The sediment trap material was weighed to determine the flux of material into the location and then the material was subsampled, prepared and analyzed for grain size, trace metal, SEM-AVS, nutrient, and organic contaminant analyses. Cores were analyzed for magnetic susceptibility, trace metal concentrations, nutrient concentrations and organic contaminants.

Difficulties Encountered

1. No difficulties encountered.
2. Due to engine problems on the pontoon boat, cores were only collected from Coggshall Cove.
3. No difficulties encountered.

Anticipated Success in Meeting Project Objectives in Scheduled Project Period

1. We are about halfway through the project one-year extension and have made good progress towards attaining our project objectives and attaining our milestones.
2. We have documented the general pattern of trace metal contamination in the NERRS area.
3. The majority of the sample analyses have been finished.
4. We documented the progressive impact of the Providence River, during ebb tide, on nutrient (nitrate, nitrite, phosphate) distributions in the NERRS area.
5. We refined the capabilities of the SubChem XZ-Profiler for chemical plume mapping and tracking. Larger wings for the Acrobat tow-body were purchased and tested. The capability for phosphate was added and demonstrated.

Preliminary Results
The following data and results are from the seasonal sampling events and the test deployments of the SubChemPak Analyzer and XZ-Profiler in Narragansett Bay. Round 1 samples were collected in November and December of 1999; Round 2 samples were collected in March and April 2000; Round 3 samples were collected in June 2000; Round 4 samples were collected in September 2000; Round 5 samples were collected in March 2001; Round 6 samples were collected in June 2001, and Round 7 samples were collected in September 2001. The core from Coggshall Cove was collected on December 5, 2001. The SubChem Systems instrumentation tests in Narragansett Bay were conducted on August 24 and 31, 2000, July 23, 2001 and November 15 and 16, 2001.

A series of intensive, combined hydrographic and chemical surveys were conducted within the Providence River and upper Narragansett Bay during November 2001. The goal was to develop and evaluate a protocol for combined sampling of currents and water column chemistry from a single ship. We also attempted to characterize both the magnitudes and patterns of circulation and chemical transport within the Providence River shipping channel and the waters to either side of Prudence Island.

Circulation patterns and energies are constrained using a RD Instruments Broadband (600 kHz) Acoustic Doppler Current Profiler (ADCP). The ADCP consists of an array of four transducers oriented such that sound beams are transmitted out 90° angles from each other and a known angle from the central axis of the instrument. The transducers emit sound pulses that are reflected by scatterers (e.g., biological and other particulate matter) throughout the water column. The reflected sound pulses are Doppler shifted due to the movement of the scatterers in the moving water. The ADCP processes the Doppler shifted return echoes to obtain along-beam velocity components that are then combined for each transducer and converted into a three-dimensional (3-D) velocity pattern. Through a process called "range gating" the ADCP listens to the returning sound pulses over uniform time increments. Progressively later time increments correspond to energy returning from greater depths. In this way velocities are resolved into depth cells, or bins. For each energy pulse sent out, (or set of energy pulses that are subsequently averaged) the resulting velocity versus depth profile is called an "ensemble". The instrument used in this study is mounted to the side of the University of Rhode Island's 55 foot research vessel the Cap'n Bert. Water column chemistry was sampled using an Acrobat device, which was towed off the back of the ship and undulates within the water column.

The first day of sampling took place on November 15, 2001 and began in the morning, just after high water (7:30 am). Survey lines were started within the shipping channel in the vicinity of Ohio Ledge (Figure 1) and ran northward along the eastern half of the channel to Fields Point area. ADCP data were collected into individual files separated by distinct sections, or reaches, of the shipping channel. A similar set of survey lines were covered running southward from Fields Point back down to the original start point on Ohio Ledge, which sampled the western half of the channel. ADCP data for each sub-section of the northward and southward running survey lines was averaged into a single profile of velocity (magnitude and direction) versus depth. Results are presented in Figures 2 and 3, and show a similar pattern, consistent with ebb conditions. During the northward running survey (Figure 2), the flow directions are nearly uniform in the vertical, with water moving in a south-southwesterly direction. Flow magnitudes varied between 30 cm/s in the surface to 5 cm/s in the bottom waters. Figure 3 shows that flow directions are predominantly to the south later in the ebb, and that flow magnitudes vary between 45 cm/s in the surface waters to 10 cm/s in the bottom waters. Very little vertical structure is seen in the water column for either northward or southward survey line.

The second day of sampling took place on November 16, 2001. A set of four transect, or survey lines were defined: Line 1 running from Greenwich Bay to Warwick Point, Line 2 from Warwick Point across to the western shore of Patience Island (e.g., crossing the upper West Passage), Line 3 running from the center of Line 2, essentially parallel to the channel up to the northern tip of Prudence Island and Line 4 running from the northern tip of Prudence Island to the eastern shore of the Bay at Colt State Park, Bristol, RI (e.g., crossing the upper East Passage). Transect lines were occupied running from west to east (Lines 1-4 in sequence) and then back again. This sampling pattern was repeated from 8:00 (high water at 8:15) through 15:15, with each line being occupied 6 times during the course of the day.

Data on circulation patterns are presented for Line 2 and 4 which define flow down either side of Prudence Island in a series of contour plots (Figures 4-5) and a plot of total integrated volume flux through each line (Figure 6). The data have been processed using a series of software codes developed at URI-GSO by Pockalny and Kincaid. The processing software utilizes GMT based commands for stripping the data of bad bins and bad ensembles using a running median filter. Filtering takes place after the velocity vectors for each depth and horizontal position have been projected into components normal to the average trend of the transect line. Data gaps are replaced with estimated values calculated from neighboring points using a cubic spline. Data are then averaged using a smoothing filter.

The contour plots provide the best representation of lateral structure in flow through each of the transect planes, which are oriented with a view looking northward, such that east (west) is on the right (left) side. The majority of the survey period covered ebb conditions. Figure 4 shows velocity contour patterns for Line 2, covering the upper West Passage from slack before ebb through to early flood conditions. During maximum ebb conditions, flow rates on Line 2 reach nearly 1 m/s, exceeding flow rates observed through Line 4 be a factor of 3. During off peak periods some lateral flow structure was observed through Line 2, with stronger flows centered on the deep channel and weaker or occasionally reversed flows on the edges of the line. Figure 5 shows a similar sequence of flow patterns for Line 4, across the upper reaches of the East Passage. Flow magnitudes are far weaker (factor of 3) than those recorded through Line 2 and are uniformly to the south.

Figure 6 shows that total ebb flux through Line 2 is nearly equal to, or slightly exceeds the total flux through Line 4, despite the fact that Line 2 covers a significantly smaller cross sectional area (Line 2 ~ 10000 m²; Line 4 ~ 35000 m²). Because the surveys ended prior to a complete tidal cycle, it is not possible to determine which side of Prudence Island receives more water, on average, from the Providence River. However, the west side clearly experiences higher flow rates.

On November 16, we used the XZ-Profiler to repeatedly survey and map the distribution of a number of parameters in the waters just North of Prudence Island. A time-series of cross-Bay transects were conducted from Greenwich Cove into the East Passage and then back, as the tide ebbed. Figure 7 illustrates concurrent measurements of density, phosphate, total nitrogen (NO2 + NO3), chlorophyll, dissolved oxygen, and current velocity collected in the autumn under presumably well mixed conditions (small density variability) for a narrow passage between the lower Providence River and the upper West Passage of Narragansett Bay.

Elevated phosphate levels (Figure 7D) were observed along the shore to the north west (Figure 7A). ADCP observations (Figure 7B) illustrate ebb tide currents, with core flow south in the center of the channel, but back flow along the north shore. The combination of these two observations suggests that phosphate is being transported from Greenwich Bay into the Providence River basin under ebb tide conditions. To further address the fate of this phosphate "plume", additional observations up bay would have been required. Regardless, these data clearly illustrate the utility of combining the XZ-Profiler with an ADCP data for small scale chemical plume tracking.

Some of the results from the July 23 and November 15-16, 2001 SubChem XZ-Profiler seasonal field surveys in Narragansett Bay are summarized and compared in Figures 8-9. Figures 8 and 9 focus on a Summer-Fall comparison of the distributions of total dissolved nitrate plus nitrite and dissolved nitrite in the Providence River between the hurricane barrier north of Fields point and Conimicut Point. The data depicted in these two figures represents the mean observed nutrient concentrations over a depth range of 3-8 meters for both summer (July 23) and autumn (November 15) conditions. Data for early ebb tide and late ebb tide were collected and are shown for both periods. It should be noted that although not evident from these plots, stratification of physical and chemical parameters was observed during the summer with a picnocline at about 5 meters (see previous Progress Report). No significant stratification of either physical or chemical parameters was observed in the autumn. Nitrogen species concentrations were found to be substantially higher in the autumn than in the summer (approximately 5X greater for NO2 + NO3, and 2X greater for NO2 alone). Two primary factors contributing to the seasonal variability of aqueous nutrients are fresh water input and level of phytoplankton activity. Each curve also exhibits along-channel variability likely related to input from two known point sources in the area: the Fields Point Sewage Treatment Plant (located north of Fields Point), and the Pawtuxet River (located across from Sabin Point). Consecutive measurements collected on both days illustrate the reproducibility of the XZ-Profiler measurements. Deviations between the curves relate primarily to tidal advective transport and mixing; on several occasions peaks can be "tracked" as they are transported down stream.

Figure 10 is a location map for the CICEET stations with core location in Coggshall Cove. Based on surface sample results, the majority of the stations in the upper mid bay are predominantly silt. Station 6 (Providence River), Station 1 (Greenwich Bay) and Stations 9 and 10 (T dock) were mostly sand (Figure 11). In a comparison of surface sediment to sediment trap trace metal concentrations (Figure 12), the concentrations of nutrients and trace metals in sediment trap material in the most northerly station (Station 6) was higher than the concentrations in the surface sediment from the same station. In general, the cadmium concentrations in the surface sediments was higher than the cadmium concentrations from the sediment trap material, however other trace metals (copper, lead, nickel) and nutrients (carbon and nitrogen) had higher concentrations in the sediment trap material than in the sediments (Figure 12).

During round 5, station 6 was the only location that had �SEM concentrations greater than AVS (Figure 13). Indicating potential trace metal bioavailability at that location. The seasonal variability of AVS was addressed in the previous progress report.

The cores from Coggshall cove had distinct lithologies. Magnetic susceptibilty was initially performed on the whole cores (Figure 14). The cores were subsequently subsampled and analyzed for trace metals, organic contaminants, nutrients and grain size. On Figure 14, the Effects Range- Low (ER-L) values are shown (vertical red lines) for cadmium, copper, lead, nickel, DDTs and PCBs. The ER-L value for PAHs is higher than the highest value encountered in the core samples. BZTs and carbon and nitrogen do not have ER-L values. There was a fairly uniform grain size over the top 20 cm. In general the trace metal and organic contaminant concentrations decreased near the surface, however, the nutrient concentrations increased (Figure 14).

As seen on Figure 14, the concentration of the C₁₀-BZTs increases with depth to a maximum at 9-10 cm and then decreases to a low level (but not background) at the bottom of the core (19-20 cm). In similar fashion, the chloro-BZT reaches a maximum at 14-15 cm and decreases to a lower value at 19-20 cm. Although the C₁₀-BZT has the higher concentration at the surface, the chloro-BZT is higher at depth as a result of the production dates of these two synthetic compounds. The former was produced from 1970 to 1985 while the latter was made during 1963 to 1985. Thus, the observed trends in this core are consistent with the production dates of these compounds. Based on these trends, we estimate that the C₁₀-BZT would reach background at about 25 cm giving an approximate sedimentation rate of 25 cm/31yr. or 0.8 cm/yr.

Concentrations of total DDTs, total PCBs and total PAHs all increase with depth and only the PCBs shows a measurable decrease in the deepest core section. Therefore, no estimate of sedimentation rates can be made using these distributions. Figure 15 shows a plot of phenanthrene/anthracene vs. fluoranthene/pyrene. All 6 of the core section are in the pyrogenic portion of the figure close to pyrogenic SRM, 1597 (coal tar). Thus, on this basis, we conclude that most of the PAHs in these samples have a pyrogenic origin as found for other urban sediments (SRMs 1944 and 1941a).

Tasks and activities for next reporting period
Over the next year, we plan on collecting sediment cores from additional locations adjacent to the NB-NEERs and analyze the sediment for trace metal and organic contaminants. Organic contaminants from sediment samples will provide additional information on the sources transport and fate of contaminants in the Narragansett Bay estuary. In the spring of 2002, we plan to conduct a comparative "wet-weather" survey using the SubChem XZ-Profiler System. The results from the spring 2001 survey will be compared to the Fall, 2001 survey.

Tasks for the next reporting period

1. Sediment core collection and analysis for magnetic susceptibility, trace metals, grain size and organic contaminants.
2. Continuation of web site development.
3. Additional XZ-Profiler survey in Narragansett Bay
4. Preparation of final report.

Work plan to accomplish tasks

1. The remaining sediment cores will be collected in the spring. Analyses will be completed and documented.
2. Web site development will continue.
3. Spring 2002 XZ-Profiler survey in Narragansett Bay
4. Final report will be drafted by September 2002 and the final report will be completed by the end of this reporting period.

Concerns or difficulties
No significant problems are anticipated.

Expenditures
The expenditures have included boat time, analytical costs, personnel costs and are within the anticipated range.