Where on Earth...? MISR Mystery Image Quiz #6: Brazil's Duck Lagoon

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This Multi-angle Imaging SpectroRadiometer (MISR) image of Brazil's Duck Lagoon covers an area of about 298 kilometers x 358 kilometers, and was captured by the instrument's vertical-viewing (nadir) camera on December 27, 2001. Answers to the questions are provided.

1. The large lagoon in the image is named for a particular type of bird. Name the bird.

   • The "Lagoa dos Patos", in the Brazilian state of Rio Grande do Sul, translates to "the Duck Lagoon". It was named by 16th century Jesuit settlers, who asked the King of Spain to grant them title to the lagoon so that they could breed ducks. The King consented, but revoked his edict when he discovered that the "duck-pond" (measuring about 14,000 square kilometers) was one of the largest lagoonal systems in the world.

2. Note the sediment plume emanating from the southern end of the lagoon. Sailors in the 16th century imagined this outlet to be the mouth of a large river. What did they call the river?

   • Early Portuguese explorers mistook the entrance to the lagoon for the mouth of a great river and called it the Rio Grande.

3. A series of wave-like points and curls form "cusps" on the inner shores of the lagoon. Which ONE of the following is most responsible for the formation of these cusps?

   1. Violent storm impacts on erosion and accretion
   2. Wind and tide-driven sediment transport and circulation
   3. Tectonic folding associated with nearby mountain ridges
   4. Bathymetric effects of dredging operations

   • Answer: B
     The lagoon's characteristics change with short-term tide-induced cyclic perturbations, and with longer term large scale meteorological conditions. The distinctive wavelike "cusps" along the inner shores result from the circulation, erosion and accumulation of sediments driven by wind and tidal action.

4. True or false: Changes in regional precipitation associated with large scale atmospheric circulation patterns have no effect on the salinity of the lagoon's water.

   • Answer: False
     The El Niño Southern Oscillation (ENSO) circulation affects precipitation amount and continental runoff, thereby changing the contents of the lagoon waters. High rainfall and increased freshwater discharge during El Niño events correspond with elevated dissolved nutrient concentrations and increased phytoplankton growth. La Niña years are dry and the associated low rainfall reduces the freshwater recharge to the lagoon, causing an increase in salinity. Occasional blooms of toxic cyanobacteria (Microcystis aeruginosa), have been registered in the lagoon when nutrient concentrations are elevated.

5. Which one of these is NOT distributed within the area covered by this image?

   1. Ruppia maritima
   2. Chelonia mydas
   3. Tapirus bairdii
   4. Microcystis aeruginosa

   • Answer: C
     A number of reeds and grasses are important to the lagoon estuary, including widgeon grass (Ruppia maritima) which reaches peak production during summer. Sea turtles (Chelonia mydas) can be found in the lagoon during spring and summer. Although the lowland tapir (Tapirus terrestris) is found in some parts of Rio Grande do Sul, the Baird's tapir (Tapirus bairdii), is not distributed within the image area (it is restricted to Central America).

Image credit: NASA/GSFC/LaRC/JPL, MISR Team.