CHAPTER 4 • Nutrients and Suspended Matter Behaviour in the Patos Lagoon Estuary (Brazil)
77
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SALINITY
Fig. 4.6. Ammonium concentrations plotted against salinity./';. surface values; V' bottom values; 0 values
from Sao Gon~alo Channel; 0 average and standard deviation from freshwater end members
resuspended sediments and enhance sediment-water exchange. The ammonium concentration in the inputs from Patos Lagoon and Sao Goncralo Channel were similar.
Concentrations in the Sao Goncralo Channel input from Mirim Lagoon are the result
of agricultural activities in that watershed and untreated sewage from the city of
Pelotas.
During cruise 8, ammonium was removed in the upper estuary and remobilized at
higher salinities exhibiting variation versus salinity similar to that observed for phosphate, nitrite and nitrate. The period between cruises 7 and 8, is usually the season of
high phytoplankton production in the Patos Lagoon Estuary (Kantin 1983) and this
probably explains the depletion of dissolved phosphate and nitrogen in the upper estuary.