Long Island Sound

Questions to Explore

Can chlorophyll concentrations serve as a water quality indicator?

How are chlorophyll concentrations influenced by rivers that enter the Long Island Sound?

Data Frames

Chlorophyll (MODIS)

Chlorophyll (SeaWiFS)

Visualizations for this Chapter

Area Plot (NEO)

Time Series (Giovanni)

Area Plot (Giovanni)

Location Map and Coordinate System

Long Island Sound (LIS) has long suffered from water quality issues due to increases in population and agricultural activities.  The water quality conditions have spurred research and policy initiatives to clean the area.

Scientists from the LIS Water Quality Program out of the Connecticut Department of Environmental Protection (CT DEP) use Dissolved Oxygen (DO) to measure the overall health of the Sound's ecosystem.  Oxygen is necessary for organisms at all levels – from fish to phytoplankton.  When large amounts of nitrogen (in the form of nitrate) enter the sound, phytoplankton grow excessively. As the phytoplankton die, their organic matter sinks to the bottom.  Bacteria consume the matter in a process (respiration) that depletes oxygen from the water.  Hypoxia – or loss of oxygen – occurs.  Without oxygen, no organisms can survive in the deeper waters, leaving only phytoplankton to thrive on the surface.

Area Plot (NEO)

1. Select Chlorophyll (MODIS).  Choose an 8 day Aqua/MODIS resolution.
2. Select the 2 time periods:                July 28 2007 – August 5 2007

   July 28 2007 – August 5 2006

3. Select the area from the Giovanni example above.
4. Compare these two time periods with the respective Dissolved Oxygen (DO) concentrations generated by the LIS Water Quality Program.

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Click here to see an time series extension that analyzes chlorophyll in relation to other environmental factors. 

Although the correlation might not be direct, nitrogen does affect chlorophyll concentrations, dissolved oxygen, and hypoxia.  To better the health of the system, policy makers want to decrease the nitrogen inputs to the sound.  Much of the nitrogen in the sound enters through the network of rivers. 

Connecticut River:  The Connecticut River, the largest river in New England, brings in 12,542.2 tons of nitrogen/year.  Nitrogen is the key limiting nutrient for the growth of phytoplankton.  Therefore, we would expect that area with high inputs of nitrogen would have higher chlorophyll concentrations.   We can examine the general impact of the rivers by averaging chlorophyll concentrations over several years.

You can locate the Connecticut River and the Thames River on the map at the following link: 

http://geology.com/state-map/maps/connecticut-rivers-map.gif

Area Plot (Giovanni)

1. Select the area specified by the geographic coordinates above.
2. Parameter: Chlorophyll (MODIS)
3. Temporal:            Begin Date = 2002, Dec

   End Date = 2007, Dec

4. Select Visualization: Lat-Lon Map, Time-Averaged
5. Generate Plot
6. Change the color bar to Custom:    Min = .5

Max = 20

Thames River:  Even though these two rivers are fairly close, there is a significant difference in the nitrogen output.  Whereas the Connecticut River inputs large amounts of nitrogen, the Thames River inputs only a small amount of nitrogen – approximately 335.6 tons/year. 

Area Plot (Giovanni)

1. Select the area specified above.
2. Parameter: Chlorophyll (MODIS)
3. Temporal:            Begin Date = 2002, Dec

End Date = 2007, Dec

4. Select Visualization: Lat-Lon Map, Time-Averaged
5. Generate Plot
6. Change the color bar to Custom:    Min = .5

   Max = 2

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Questions for further investigation

• Is there a relationship between dissolved oxygen and chlorophyll?  Between hypoxia and chlorophyll? Between nitrogen and chlorophyll?  Which has the strongest relationship? Describe the interactions between these indicators. 
• How and why does the chlorophyll concentration estimated by the satellite observations differ from the chlorophyll measured directly from water samples? 
• How could the SeaWiFS and MODIS chlorophyll data be useful for policy makers?  Write a brief statement to the LIS Water Quality Program outlining how they could integrate the remote sensing data in their monitoring program. 
• Map the flow of chlorophyll a (SeaWiFS) from the mouth of the Connecticut River.  During what months and where would you predict hypoxia to occur?

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