Methods

A total of six seasonal, interdisciplinary cruises, each of 9 days duration, were carried out in the ETM region of the upper Chesapeake Bay during May, July, and October of 2001 and 2002. Daylong axial surveys were carried out before, between, and after the seasonal cruises at approximately 6-week intervals. In this chapter, we concentrate on the seasonal cruises carried out during 2002, since these cruises yielded the most complete and reliable data sets on particle characteristics. During each of the seasonal cruises, an initial rapid axial survey was run from the R/V Cape Henlopen to locate the ETM, after which reference moorings were deployed and fisheries surveys were carried out. A full axial survey with suspended sample collections and coordinated lateral sampling followed. Lateral sampling was carried out using the R/V Coot, a small, shallow draft vessel outfitted with a similar set of instrumentation to that used on the Henlopen. The remainder of each cruise was taken up by additional full axial/lateral sampling, 6-h repeated surveys in the vicinity of the ETM, 12-h tidal cycle surveys concentrating on interactions between turbulence and particle characteristics, bottom sediment sampling and erodibility testing, and zooplankton/fish sampling.

Three full axial surveys were conducted during the May 2002 cruise, and four axial surveys during both the July and October 2002 cruises. Each survey consisted of 12 to 14 stations up the shipping channel, spaced approximately 6 km apart (Figure 10.1). They began near the Chesapeake Bay Bridge before maximum tidal current and ended near Turkey Point shortly after maximum tidal current. Both flood and ebb tides were surveyed. Profiles were taken at each station with a SBE 9/11 CTD equipped with a Downing and Associates OBS-3a backscatterance sensor and a Sea Tech 5 cm pathlength transmissometer. A Sequoia Scientific LISST-100C (Laser in situ Scattering and Transmissometry) and well pump were mounted at the same elevation and in close proximity to the OBS, transmissometer, and CTD sampling pump. The sample volumes of the LISST-100C and transmissometer were oriented horizontally and centered over a large open space in the CTD frame to ensure sampling of an undisturbed water column during profiling. Only data collected on the downcast were analyzed. Pump samples collected with the well pump were used for TSS calibrations for the OBS, transmissometer, and LISST-100C. Data were interpolated onto a uniform grid at 0.5 m vertical resolution and 3 km horizontal resolution using the kriging algorithm in Surfer (Golden Software), and contoured using the same software.

The LISST-100C measured optical transmission and multi-angle forward scattering of a 670 nm laser. The LISST sampled at a rate of 5 Hz. Five samples were averaged and recorded to an internal datalogger at a rate of 1 Hz. An optically transparent path reduction module was added to the LISST, reducing the optical path length from 5 to 2.5 cm and effectively doubling the maximum concentration in which the instrument could operate from «80 to «160 mgl-1. Optical percent transmission data were converted to total suspended solids (TSS, mgl-1) using

- -x- - May

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—o - July

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—a— October

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