The Influence of Local and Non-Local Forcing Effects on the Subtidal Circulation of Patos Lagoon

Abstract

Some basic features concerning the subtidal circulation of Patos Lagoon were studied through time series analysis of wind, freshwater discharge, and water level records, as well as by means of experiments carried out with a 3D numerical model. The results indicate that during low to moderate river discharge the wind is the main forcing mechanism in time scales associated with meteorological fronts. The two types of wind action, local and non-local effects, are distinguished and their relative importance is evaluated. Salt water enters the system due to a combination of both remote and local wind effects that favors the development of a pressure gradient towards the lagoon during southwesterly winds. This situation is reversed when northeasterly winds dominate. In the inner parts of the lagoon, local wind plays the major role by inducing set up/set down oscillations. An upwind return flow is then developed under these conditions. During high flood periods, normally observed in late winter, the circulation is driven by freshwater discharge.

Trophic quality of waters in the Patos Lagoon estuary: a comparison between its margins and the port channel located in Rio Grande, RS, Brazil

“…The maximum value was found in spring, i. e. 260 mg.L -1 at SM2 site. Salinity in the sampling periods is in agreement with the seasonal pattern established by Möller et al (2001): summer had the highest salinity (the maximum was 34.3), fall showed had mixoaline salinity, ranging from 9.6 to 16.8, winter showed almost low salinity (between 0.3 and 3.2) and spring had strongly mixoaline waters. This parameter differentiated, with no pattern, the environment in the inlet and the channel: the salinity at Saco da Mangueira is lower than the one at the Rio Grande Channel in summer and spring.…”

“…The Patos Lagoon estuary, in southern Brazil, has a narrow channel that restricts the tidal influence, which has a low range (0.47 m) (Möller et al, 2001). Geomorphological events in the late Pleistocene created the original estuarine conditions.…”

A modeling study of Patos lagoon (Brazil) flow response to idealized wind and river discharge: dynamical analysis

“…The central lagoon is formed by the area between Ponta da Feitoria and the mouth of the Lagoa do Casamento (Delaney, 1965). The lower and central areas are separated by a morphological step with local depth of less than 1 m, formed by sandy banks situated around Ponta da Feitoria (Moller et al, 2001) (Fig. 1).…”

Use of a mathematical model to estimate the impact of shrimp pen culture at Patos Lagoon estuary, Brazil

“…The estuary can be divided in two major areas (Bonilha and Asmus 1994): a central water body with deep channels and several protected shallow bays, with depths ranging from of 0.5 to 3m (Castello 1985).According to Seeliger and Kjerfve (2001), the main factors that determine the hydrodynamics of the Patos Lagoon estuary are fluvial discharge, tidal variation and wind regime. However, due to the low amplitude of tidal variation (mean of 0.30 m), its influence is minor (Möller et al 2001). Patos Lagoon can be considered a river-dominated estuary (Möller et al 2001(Möller et al , 2009.…”

“…However, due to the low amplitude of tidal variation (mean of 0.30 m), its influence is minor (Möller et al 2001). Patos Lagoon can be considered a river-dominated estuary (Möller et al 2001(Möller et al , 2009. When river discharge is below average (~2400 m 3 s -1…”