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Sediment. Turbidity Maxima. Nitrogen, Oxygen, Chlorophyll & Absorption at 4m Depth . Chlorophyll Conc. (µg/L). Nitrogen & Oxygen Conc. (µM). River Distance (km). Profiling the Optics, Sediment, and Phytoplankton in the Delaware Bay. Jacqueline McSweeney 1 , John Wilkin 2 , Bob Chant 2
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Nitrogen, Oxygen, Chlorophyll & Absorption at 4m Depth
Chlorophyll Conc. (µg/L)
Nitrogen & Oxygen Conc. (µM)
River Distance (km)
Profiling the Optics, Sediment, and Phytoplankton in the Delaware Bay
Jacqueline McSweeney1, John Wilkin2, Bob Chant2
1 Department of Chemistry and Biochemistry, Loyola Marymount University, 2 Institute of Marine and Coastal Sciences, Rutgers University
Phytoplankton growth is dependent on both light and nutrients. Previous studies of the Delaware estuary have indicated that it is nutrient-rich, but that primary productivity is limited by light availability (Pennock 1985). This project aims to relate the optical behavior to sediment concentration and then to relate the absorption variation down the river to observed phytoplankton growth. The hypothesis is that suspended matter increases the total absorption of light and thus limits the phytoplankton growth in the estuary.
A secondary purpose is to parameterize an optical model of the estuary in Regional Ocean Modeling System (ROMS) by determining specific conditions, such as absorption coefficients of sediment and chlorophyll, from the observations. The model will then be used to test the sediment-light limitation hypothesis.
ROMS model run with and without sediment parameters
Chlorophyll, OBS and PAR in the Delaware
Data collection was conducted via the RV Hugh R. Sharp during a cruise June 3-5, 2010. Temperature, salinity, depth, and optical backscatter (OBS), were measured with a CTD package further equipped with a Chelsea Aquatraka, an Aanderra Optode, and a Satlantic SUNA to measure fluorescence, oxygen, and nitrogen. Optical data was collected using a Profiling Radiance Radiometer 600 (PRR) from Biospherical Instruments Inc. The ship stopped at 22 stations (Figure 1), but the PRR was only deployed at 19 since data could only be collected during daylight.
The PRR and CTD data was then processed using Matlab. Since the PRR data collected optical profiles at six specific wavelengths, the Photosynthetically active radiation (PAR) was approximated by using the below equation to calculate the shaded area in Figure 2.
Figure 4. Color plot of chlorophyll (µg/L), gray-scale contour plot of OBS (V) and red plots of PAR (W/m2) penetration according depth and river distance. The
Sinks → Settles → Erodes → Resuspends
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Figure 5. Average concentrations of nitrogen(red), oxygen (blue), and chlorophyll
(green) from the surface to a 4 m depth are plotted against river distance.
Absorption coefficients (multiplied by a correction factor) were plotted along the
same axis (black) to show the relative relationship between chlorophyll and light
attenuation. Below equations were used to calculate the absorption coefficients (b) .
Light decay is exponential when b is constant. In reality, b is a function of depth (z),
so irradiance (I) won’t decrease exponentially.
This work was made possible due to the support of the National Science Foundation and the Regional Ocean Modeling System group. Special thanks to the following people/groups who contributed in a significant way to the progression of the project: Maria Aristizabal, Dove Guo, Eli Hunter, Chip Haldeman, Matt Taynor and those colleagues from University of Delaware collaborating in data collection from the Delaware River. Thank you! :)
Figure 2. Example graph of the approximation of PAR from a typical
spectrum. The black curve is the actual irradiance over a wavelength
range of ≈ 400-700 nm and the shaded area is the approximated PAR.
Figure 1. Map of the 22 sampling stations in the Delaware River.
Equation 1. PAR values were calculated by approximating the integration of irradiance (a function of wavelength) from 400 to 700 nm.