Project Title:

"Developing and Applying a New In Situ Technology for the Investigation of Episodic Contaminant Transport Events Within Estuaries"

Project Coordinator (Lead Principal Investigator):

John W. King, University of Rhode Island

Additional Principal Investigators:

Alfred K. Hanson, Jr., SubChem Systems, Inc.
Christopher R. Kincaid, University of Rhode Island
Elizabeth Lacey, University of Rhode Island
James G. Quinn, University of Rhode Island

Project Duration: 10/1999-9/2001

Project Location: Narragansett Bay NERR including regions adjacent to the NERR site.

Abstract

Seasonal and episodic events such as tidal and wind driven currents, rainstorms, channel dredging, discharges from sewage treatment plants, and ship activities may lead to the resuspension of sediments and significant changes in the concentration of dissolved oxygen, chemical contaminants and nutrients in coastal marine waters. We are using a combination of new and traditional technologies to characterize the water and sediment quality before, during and after resuspension events in the Narragansett Bay National Estuarine Research Reserve (NB-NEER). New technology used for this project includes the combination of in situ chemical analysis (dissolved oxygen, iron, chlorophyll), hydrographic (salinity, temperature, density) and current velocity and direction measurements. Traditional technology used for this project includes the collection of surficial sediments and analysis for total metals, sediment grain size, and Simultaneously Extracted Metals-Acid Volatile Sulfide, and analysis of suspended particulate matter captured in sediment traps. A preliminary cruise combining the new in situ chemical analysis system (SubChem) with current velocities and directions was performed in December 1999, and surface sediment samples were collected and sediment traps deployed in November and December 1999.

Description of Objectives

The objectives of the study are two-fold. First, we will combine newly-developed and existing technologies in an innovative manner to document the effects of natural and anthropogenic episodic events on the input, transport and fate of nutrients, oxygen, and organic and inorganic contaminants in an urban estuary. Second we will apply our findings to improve existing risk-characterization schemes for urban estuaries. During the first year of funding, we are concentrating on the first objective.

Instrumentation Development Status

During the past five months SubChem’s R&D effort primarily involved minor functional improvements, analytical calibration and in-water testing of the SubChemPak AnalyzerTM. Laboratory calibration experiments were conducted with flowing seawater for the simultaneous determination of dissolved nitrite and iron(II). With the successful completion of these laboratory tests, it was decided that the SubChemPak Analyzer was ready for submerged testing.

The SubChemPak Analyzer has been designed to be co-deployable with standard oceanographic electronic profiling packages (i.e. CTD’s). To best demonstrate this capability, the SubChemPak was set up for co-deployment with a Sea Bird Electronics CTD plus bio-optical sensor system for the in-water tests and capability demonstrations. The CTD-plus system included a Sealogger model 25 with modular sensors for the measurement of conductivity (salinity), temperature, pressure (depth), density (calculated), dissolved oxygen, pH, chlorophyll fluorescence, light transmission (beam attenuation coefficient), and PAR (photo-synthetically active radiation). All the instrumental components were attached to a steel cage for functional deployment from a ship using a winch and davit. A 30-meter long underwater umbilical was assembled that included the CTD sea-cable, the SubChemPak sea-cable and plastic tubing for water sample collection by a pump-to-surface technique. The complete electronic profiling package (see photo) is ~1 m high and weighs ~150 lbs in air.

A new deck box was designed and assembled with required electronics for instrument power and data communication between the underwater instruments and two notebook computers. The two notebook PCs controlled the submerged instruments operation and acquired and displayed the real-time data stream. One PC was dedicated to the SubChemPak Analyzer and the other to the Sea Bird CTD system.

Description of Field and Analytical Methods

On November 19, 1999 and December 20, 1999, surface sediment samples were collected and sediment traps deployed from 8 stations around the NB-NERR area (Figure 1). Surface samples were collected using a Smith MacIntire grab sampler. The top 2 cm were subsampled in the field using teflon coated titanium tools and stored in cleaned containers. Mini cores (up to 13 cm in length) were collected from a subset of stations and then subsampled at 2 cm increments down the core. The surficial sediments are in the process of being analyzed for SEM-AVS, total trace metal concentration, grain size, and nutrient concentrations. The subsampled mini cores are being analyzed for total trace metal concentrations and sediment grain size.

 

A series of in water test deployments were conducted with the SubChemPak Analyzer and Sea Bird CTD system during December. The initial submerged experiments were conducted in 5 meter deep tanks of seawater (Figure 2), located at URI’s Marine Ecosystem Research Laboratory (MERL tests 1 and 2 on 12/3/99 and 12/10/99). The SubChemPak Analyzer was also tested in the waters of Narragansett Bay aboard URI Ocean Engineering’s research vessel, the CT-1, on December 20, 1999(Figure 3). For all of these tests the SubChemPak Analyzer was set up for the simultaneous determination of the trace nutrients, dissolved nitrite and iron(II). The major objectives for the MERL tank experiments were to: (1) Test the integrity of the pressure housing seals and electronic and fluidic connections. (2) Test and evaluate the in situ analytical calibration feature. (3) Test and evaluate the function of the in-line heater in cold water (5-7 C). (4) Evaluate different devices for bubble removal prior to the detector inlets.

 

Figure 2. Photographs of the SubChemPak Analyzer and CTD electronic profiling system being tested in a 5-meter test tank (URI-MERL facility).

On December 20, 1999 a research cruise in the upper portion of Narragansett Bay was performed aboard the R/V CT-1 utilizing a ship-mounted RDI 600 kHz Acoustic Doppler Current Profiler (ADCP) and the SubChemPak Analyzer and Sea Bird CTD system. One transect was performed (A-B on Figure 1) across the bay.

The primary objectives for the first deployment of the SubChemPak Analyzer in Narragansett Bay, aboard the CT-1, were: 1) To demonstrate the capability of the SubChemPak Analyzer for accurate and reliable nutrient measurements in the field. 2) To initiate the technological integration of ADCP measurements of current velocity and direction (Kincaid group) with simultaneously acquired data from the SubChemPak Analyzer and CTD electronic profiling system. 3) To collect water samples from discreet depths that could be used for verification of the new in situ chemical measurement technology and for the analysis of other chemicals and contaminants that were not determined in situ.

 

Figure 3. Photograph of the electronic profiling system, with SubChemPak Analyzer, being deployed off the stern of the URI-OE R/V CT-1 in the Providence River region of Narragansett Bay (12/20/99).

The preliminary analysis of the results of these submerged tests were very encouraging. There were no leaks during any of the deployments (0-10 m depth). Our initial evaluation of the calibration data (Figure 4) indicates that the in situ calibration feature works very well, and that the SubChemPak Analyzer is capable of producing accurate analytical results while submerged.

Figure 4. Comparison of SubChemPak Analyzer calibration data for dissolved nitrite and iron(II) from laboratory and submerged in test tanks and Narragansett Bay.

During the December 20, 1999 cruise, vertical casts with the SubChemPak Analyzer and ADCP vertical measurements were performed at three stations (Stations 6, 7, and 8 on Figure 1) while drifting slowly with surface currents. The preliminary results from Station 6 & 7 are shown in Figures 5 & 6 to give an example of the type of data we can presently acquire and the information that it can provide about chemical contaminant transport in the NB-NEERS.

 

Figure 5. Vertical profiles obtained for one of the casts in Narragansett Bay (Station 6) located in the Providence River area, north of the NB-NEERS. The profiles include data from the CTD, bio-optical sensors, the SubChemPak Analyzer and the ADCP (Kincaid group). All the parameters plotted were measured simultaneously, and in real-time, during the deployment. (The coincident CTD and SubChemPak data are binned at 1 sample per second. The ADCP data is binned at 1- meter intervals).

The vertical cast at station 6 (Figure 5) was taken at approximately 12:17 PM local time, during slack low-tide. Water velocities at that station were appropriately low, below 10 cm/s, and spanned a whole range of directions. The CTD data (panel a) indicated a stratified water column with cooler, lower salinity water overlying denser waters that were warmer and saltier. An intense plume of phytoplankton (i.e. BAC and chlorophyll pigments) was embedded in the water column from 1-4 meters depth. These particle laden, pigmented waters also exhibited higher oxygen levels and a distinct pH gradient to higher levels with depth (panel b). Dissolved nitrite generally decreased with depth with a sharper gradient in deeper waters (panel c). Surprisingly high and variable levels of dissolved iron(II) were present in the water column at this station. We hypothesize that this anomalous plume of iron(II), is a thermodynamically unstable or transient signal, that emanated from a sewage treatment plant located near the sampling site. This plume was not apparent by Station 7 (see below). We plan to examine this phenomena in more detail during future cruises.

The vertical cast at station 7 (Figure 6) was taken at approximately 1:13 PM local time, at the beginning of the incoming tide. The CTD data (panel a) indicated a shallow layer of cool, lower salinity water (0-2 m) overlying denser waters (2-8 m) that were warmer and saltier. The shallow surface layer had elevated chlorophyll pigment levels, higher oxygen and lower pH levels, than the bottom layers (panel b). Dissolved nitrite decreased with depth and iron(II) increased with depth in the water column (panel c). Water velocities (panel d) were quite low in the top four meters, but increased to approximately 18 cm/s in the lower water column, at an average direction of 315 degrees (magnetically corrected). The in situ trace chemical profiles for nitrite and iron(II) exhibited a sharp discontinuity near 5.5 meters depth that is attributed to current shear associated with the incoming tide (northerly velocity component).

This new in situ technology/instrument system for detecting and tracking chemical plumes is presently under development and the results shown in this progress report are preliminary subject to further evaluation and comparison with the results of the trace metal and nutrient analyses on the discreet samples, and other verification tests yet to be completed. We are presently analyzing the discrete water samples that were collected during this field experiment for nutrients and trace metals. The analytical results for dissolved iron and nitrite from the discrete samples will be used to verify the accuracy of the in situ results obtained with the SubChemPak Analyzer.