12 The Patos Lagoon Estuary, Brazil
u. SEELIGER
12.1 Introduction
The dominant feature of the southern Brazilian coastal plain is the PatosMirim Lagoon complex, the Patos Lagoon (10,360 km 2 ) being the world's
largest choked lagoon. About 80% of the lagoon is a freshwater system but
at its southern reach (32°S), where the lagoon connects to the Atlantic
Ocean, brackish waters and fringing marshes comprise an estuarine ecosystem of approximately 1,000km 2 (Fig. 12.1). The estuary performs critical interface functions between the limnic areas of the Patos Lagoon and
the shelf waters of Subtropical Convergence regions in the southwestern
Atlantic. The passage of continental freshwater runoff from the drainage
basin (-200,000 km 2 ) through the estuary and the intrusion of seawater
into it establish the physico-chemical characteristics which control ecological processes and vital habitats for the successful reproduction and/or
growth of many commercially important marine species which visit the
estuary periodically.
12.2 Environmental Setting
As is characteristic of choked lagoons, the deep (15m) and narrow (800 m)
inlet of the Patos Lagoon acts as a set-down filter and strongly attenuates
the advance of tidal waves (0.47 m) into the estuary, thus estuarine water
levels and currents are closely linked to regional precipitation and wind
patterns. The dominant northeasterly winds (mean 5 m s- 1 ) promote flushing of the estuary, owing principally to the formation of a north-south
pressure gradient inside the lagoon and to the retreat of nearshore coastal
water. Especially in winter, the entire system becomes freshwater during
prolonged periods, when runoff volumes and velocities in the inlet may
reach 22,000 m 3 s- 1 and 1.9 m s- 1 , respectively. In contrast, the southerly
Ecological Studies, Vol. 144
U. Seeliger and B. Kjerfve (eds.)
Coastal Marine Ecosystems of Latin America
©Springer-Verlag Berlin Heidelberg 2001
u. SEELIGER
12.1 Introduction
The dominant feature of the southern Brazilian coastal plain is the PatosMirim Lagoon complex, the Patos Lagoon (10,360 km 2 ) being the world's
largest choked lagoon. About 80% of the lagoon is a freshwater system but
at its southern reach (32°S), where the lagoon connects to the Atlantic
Ocean, brackish waters and fringing marshes comprise an estuarine ecosystem of approximately 1,000km 2 (Fig. 12.1). The estuary performs critical interface functions between the limnic areas of the Patos Lagoon and
the shelf waters of Subtropical Convergence regions in the southwestern
Atlantic. The passage of continental freshwater runoff from the drainage
basin (-200,000 km 2 ) through the estuary and the intrusion of seawater
into it establish the physico-chemical characteristics which control ecological processes and vital habitats for the successful reproduction and/or
growth of many commercially important marine species which visit the
estuary periodically.
12.2 Environmental Setting
As is characteristic of choked lagoons, the deep (15m) and narrow (800 m)
inlet of the Patos Lagoon acts as a set-down filter and strongly attenuates
the advance of tidal waves (0.47 m) into the estuary, thus estuarine water
levels and currents are closely linked to regional precipitation and wind
patterns. The dominant northeasterly winds (mean 5 m s- 1 ) promote flushing of the estuary, owing principally to the formation of a north-south
pressure gradient inside the lagoon and to the retreat of nearshore coastal
water. Especially in winter, the entire system becomes freshwater during
prolonged periods, when runoff volumes and velocities in the inlet may
reach 22,000 m 3 s- 1 and 1.9 m s- 1 , respectively. In contrast, the southerly
Ecological Studies, Vol. 144
U. Seeliger and B. Kjerfve (eds.)
Coastal Marine Ecosystems of Latin America
©Springer-Verlag Berlin Heidelberg 2001