Project Title: Developing and Applying A New In Situ Technology for the Investigation of Episodic Contaminant Transport Events within Estuaries (Year 3)
Principal Investigator(s): Alfred K. Hanson, Christopher R. Kincaid, Elizabeth Lacey Laliberte, James G. Quinn

Accomplishments
Scheduled Tasks:

1. Collection and analysis of remaining sediment core.
2. Further develop automated MatLab data processing routines for merging SubChem XZ-Profiler data.
3. Poster presentation of paper at AGU Ocean Sciences 2002 (Hawaii) "In Situ Mapping of Horizontal and Vertical Nutrient Gradients in Narragansett Bay, RI" by Peter Egli, William Deleo and Alfred Hanson of SubChem Systems, Inc.

Progress on Tasks
1a) On May 24, 2002 four sediment cores were collected from Potter Cove adjacent to Prudence Island, in Narragansett Bay.

1b) All of the cores were analyzed using magnetic susceptibility. Based on the magnetic susceptibility results, one core (PC-4) was chosen for intensive study.

1c) Selected intervals of PC-4 were subsampled for the determination of trace metal, grain size, organic contaminant, nutrient, and lead-210 concentrations.

2) MatLab code has been written to aid in processing the SubChem data.

Difficulties Encountered
No difficulties encountered.

Anticipated Success in Meeting Project Objectives in Scheduled Project Period
It is anticipated that all the objectives will be met within the project period.

Preliminary Results
Four sediment cores were collected from Potter Cove (Figure 1) adjacent to Prudence Island on May 24, 2002. The cores were collected in the eastern side of the Cove. The length of the cores ranged from 92.5 cm (PC-4) to 123 cm (PC-1).

An initial screening of the cores was performed using magnetic susceptibility. Magnetic susceptibility measures the relative concentration of magnetic minerals within a sample. Based on field observations (e.g., quality of the sediment/water interface) and the magnetic susceptibility results (Figure 2), PC-4 was selected for intensive study.

PC-4 was subsampled for trace metal (cadmium, copper, lead, nickel and zinc), grain size, organic contaminants, nutrient (carbon and nitrogen) and lead-210 concentrations. For the determination of trace metal concentrations, freeze-dried sediment was treated with concentrated nitric, hydrochloric and hydrofluoric acids and placed in a heated sonicator for greater than 48 hours. Grain size samples were prepared by treating wet sediment with acetic acid and hydrogen peroxide to remove the carbonates and organic material. The sediment was wet sieved and the less than 63 micron fraction was run through an Elzone particle size analyzer. Figure 3 shows the trace metal concentrations with depth for the core PC-4. Figure 4 provides grain size information and shows trace metals concentrations normalized by grain size. Cadmium, copper, lead and zinc all show surfical increases. In addition, copper and lead have distinct subsurface peaks at 9 cm. Examination of both the trace metal and grain size-normalized trace metal data for cadmium, copper, lead and zinc shows an increase in concentrations around 17 to 19 cm. The trace metal values were compared to the "Effects Range-Low" and "Effects Range-Median" values for each of the trace metals. All of the cadmium concentrations were below the ER-L (Figure 3). Copper and lead had surficial concentrations between the ER-L and ER-M. All of the nickel samples were between the ER-L and ER-M. Zinc was the only trace metal that was found in concentrations above the ER-M. The surface sample was above the ER-M and other samples were above the ER-L (including the sample at 51 cm). The grain size normalization resulted in comparatively lower surficial concentrations (Figure 4).

We also analyzed 6 sections of core PC-4 for organic contaminants. Values for the BZTs, PAHs and TPHs generally decrease to low levels at the bottom (14-16 cm) and the Chlordanes were not detectible (< 0.5 ppb) in this core. Two of the contaminants (∑DDTs and ∑PCBs) increased to a maximum value at 10-12 cm followed by a rapid drop in concentration at the core bottom (Figure 5). In addition, these two contaminants exceeded the ERL guidelines for all but the deepest section of the core. Based on the observed distribution of the C10-BZT, we would estimate it reaching background (~10 ppb) at about 16 cm giving an approximate sedimentation rate of 16 cm/32 yr. or 0.50 cm/yr. However, given that the approximate dates of introduction into the environment are 1930 for PCBs and 1940 for DDTs, the low levels of these compounds, as well as the BZTs, at 15 cm suggests that there has been some mixing of the sediments at this station. Thus, a realistic estimate of sedimentation rate using this limited data set is not possible at this site. Additional information from the lead-210 dating (see Task II below) should aid in sediment rate determination. Based on a plot of phenanthrene/anthracene vs. fluoranthene/pyrene (indicators of petrogenic versus pyrogenic sources), most of the PAHs in these samples have a pyrogenic origin as found for other urban sediments.

Tasks and activities for next reporting period

Tasks for the next reporting period

1. XZ-Profiler pre/post wet event surveys in Narragansett Bay
2. All of the remaining analyses (i.e., Pb-210, nutrients) will be performed and documented. A summary report will be prepared. Information regarding the project will be disseminated.

Work plan to accomplish tasks
1) Fall 2002 XZ-Profiler pre/post wet event survey in Narragansett Bay.

2a) A summary report will be prepared.

2b) The abstract "Contaminant Redistribution and Remobilization in an Urbanized Estuary" (E. Laliberte, J. King, J. Quinn) was accepted and there will be a poster presentation at the SETAC 23rd Annual Meeting, 16 - 20 November 2002, in Salt Lake City, Utah.

Concerns or difficulties
No difficulties are anticipated.

Expenditures
The expenditures are within the anticipated range.