ABSTRACT The direct influence of freshwater discharge along the coastal regions is observed in several processes following a wide spectrum on spatial and temporal variability. The knowledge of relative importance of this physical forcing is fundamental by the correct management of the coastal sites and the understanding of consequences associated with processes of climatic order is one point deserves some investigation. The major part of the studies in the Patos Lagoon, located in the southernmost part of Brazil, is limited to investigate the effects in synoptic time scales. In this way, the objective of this study is to investigate the long term variability pattern of the Patos Lagoon discharge and water levels indentifying long term trends through wavelet analysis. The results indicated that El Ni?o (La Ni?a) events promote the intensification (decrease) of the freshwater intensity in the principal river tributaries of the Patos Lagoon following scales from 16 to 120 months (from 1.3 to 10 years). The most energetic cycle is centered in periods of 64 months (5.3 years). The longer events reflect the long term response of the non linear dynamics in Equatorial Pacific changing the precipitation pattern, principally during winter and at the end of spring and early autumn. The non-linear long term trend indicates a pattern with values of discharge normally above (below) the mean after (before) 1970’s. An increasing trend starting after 1970 possibly indicates a longer term cycle influencing the interannual variability of the Patos Lagoon discharge. The seasonality is maintained in climatic monthly means obtained after and before 1970’s, but, with mean increase around 364 m3·s?1 in freshwater discharge with reduced amplitude of the seasonal cycle.
Cite this paper
W. Marques, "The Temporal Variability of the Freshwater Discharge and Water Levels at the Patos Lagoon, Brazil," International Journal of Geosciences, Vol. 3 No. 4, 2012, pp. 758-766. doi: 10.4236/ijg.2012.34076.
 J. R. Schubel and D. W. Pritchard, “Responses of Upper Chesapeake Bay to Variations in Discharge of the Susquehanna River,” Estuaries, Vol. 9, No. 4, 1986, pp. 236-249. doi:10.2307/1352096
 T. A. Denes and J. M. Caffrey, “Changes in Seasonal Water Transport in a Louisina estuary, Forleague Bay, Louisiana,” Estuaries, Vol. 11, No. 3, 1988, pp. 184-191.
 T. Yanagy, “Currents and Sediment Transport in the Seto Inland Sea, Japan,” In: R. T. Cheng, Ed., Residual Currents and Long-Term Transport (Coastal and Estuarine Stud- ies), Springer Verlag, New York, 1990, pp. 348-355.
 R. J. Uncles and J. A. Stephens, “Buoyancy Phenomena in the Tweed Estuary,” Buoyancy Effects on Coastal and Estuarine Dynamics (Coastal and Estuarine Studies), 1996, pp. 175-193.
 J. Dronkers, “The Influence of Buoyancy on Transverse Circulation and on Estuarine Dynamics,” Buoyancy Effects on Coastal and Estuarine Dynamics (Coastal and Estuarine Studies), 1996, pp. 341-356.
 L. A. Cifuentes, L. E. Schemel and J. H. Sharp, “Quali- tative and Numerical Analyses on the Effects of River Inflow Variations on Mixing Diagrams in Estuaries,” Es- tuarine, Coastal and Shelf Science, Vol. 30, No. 4, 1990, pp. 411-427. doi:10.1016/0272-7714(90)90006-D
 I. Grabemann, H. Kühle, B. Kunze and A. Müller, “Studies on Transport Times and Water Quality in the Weser Estuary (Germany),” Mixing in Estuaries and Coastal Seas, (Coastal and Estuarine Studies), American Geophysical Union, Washington DC, 1996, pp. 291-302.
 P. H. Doering and R. H. Chamberlain, “Water Quality and Source of Freshwater Discharge to the Caloosa- hatchee Estuary, Florida,” Journal of the American Water Resources Association, Vol. 35, No. 4, 1999, pp. 793-805.
 D. A. Jay, “Residual Circulation in Shallow Estuary: Shear, Stratification and Transport Processes,” In: R. T. Cheng, Ed., Residual Currents and Long-term Transport. Coastal and Estuarine Studies, Springer Verlag, New York, 1990, pp. 49-78.
 A. Y. Kuo, J. M. Hamrick and G. M. Sisson, “Persistence of Residual Currents in the James River Estuary and Its Implication to Mass Transport,” In: R. T. Cheng, Ed., Residual Currents and Long-term Transport. Coastal and Estuarine Studies, Springer Verlag, New York, 1990, pp. 389-402.
 O. O. M?ller, J. A. Lorenzzetti, J. L. Stech and M. M. Mata, “The Patos Lagoon Summertime Circulation and Dynamics,” Coastal Shelf Research, Vol. 16, 1996, pp. 335-351.
 O. O. M?ller, P. Castaing, J. C. Salomon and P. Lazure, “The Influence of Local and Non-Local Forcing Effects on the Sub Tidal Circulation of Patos Lagoon,” Estuaries, Vol. 24, No. 2, 2001, pp. 297-311. doi:10.2307/1352953
 E. H. L. Fernandes, K. R. Dyer, O. O. M?ller and L. F. H. Niencheski, “The Patos Lagoon Hydrodynamics during an El Ni?o Event (1998),” Continental Shelf Research, Vol. 22, No. 11-13, 2002, pp. 1699-1713.
 E. H. L. Fernandes, K. R. Dyer and O. O. M?ller, “Spatial Gradients in the Flow of Southern Patos Lagoon,” Journal of Coastal Research, Vol. 21, No. 4, 2005, pp. 759-769.
 W. C. Marques, E. H. Fernandes and L. A. O. Rocha, “Straining and Advection Contributions to the Mixing Process of the Patos Lagoon Estuary Brazil,” Journal of Geophysical Research, Vol. 116, 2011, 11 p.
 W. C. Marques, E. H. Fernandes, I. O. Monteiro and O. O. M?ller, “Numerical Modeling of the Patos Lagoon Coastal Plume, Brazil,” Continental Shelf Research, Vol. 29, No. 3, 2009, pp. 556-571.
 W. C. Marques, , E. H. Fernandes and O. O. M?ller, “Straining and Advection Contributions to the Mixing Process of the Patos Lagoon Coastal Plume, Brazil,” Journal of Geophysical Research, Vol. 115, 2010, 23 p.
 W. C. Marques, E. H. Fernandes, B. C. Moraes, O. O. M?ller and A. Malcherek, “The Dynamics of Patos Lagoon Suspendeds Sediment Plume and Its Contribution for the Deposition Pattern in the Southern Brazilian Inner Shelf,” Journal of Geophysical Research, Vol. 115, 2010, 22p. doi:10.1029/2010JC006190
 W. C. Marques and O. O. M?ller, “Variabilidade Tem- poral Em Longo Período da Descarga Fluvial e Níveis de água da Lagoa dos Patos, Rio Grande do Sul, Brasil,” Revista Brasileira de Recursos Hídricos, Vol. 13, 2009, pp. 155-163.
 M. Rocherfort, “Rapports Entre la Pluviosité et l’écoulement dans le Brasil Subtropical et le Brasil Tropical Atlantique,” Travaux et Mémoires de l’Institu des Hautes Etudes de l’Amérique Latine, Paris, France, 1958.
 C. Torrence and G. P. Compo, “A Practical Guide to Wavelet Analysis,” Bulletin of the American Meteorological Society, Vol. 79, 1998, pp. 61-78.
 I. Daubechies, “The Wavelet Transform Time-Frequency Localization and Signal Analysis,” IEEE Transactions on Information Theory, Vol. 36, No. 5, 1990, pp. 961-1004.
 B. Kjerfve, “Coastal Lagoons,” In: B. Kjerfve, Ed., Coas- tal Lagoon Processes, Elsevier Oceanographic Series 60, Amsterdam, 1994, pp. 1-8.
 N. P. Smith, “Water, Salt and Heat Balance of Coastal Lagoons,” In: B. Kjerfve, Ed., Coastal Lagoon Processes, Elsevier Oceanography Studies, Amsterdam, 1994, pp. 69-101.
 W. W. Schroeder, S. P. Dinnel and W. J. Wiseman Jr., “Salinity Stratification in a River-Dominated Estuary,” Estuaries, Vol. 13, No. 2, 1990, pp. 145-154.
 W. C. Marques, “Estudo da Dinamica da Pluma Costeira da Lagoa dos Patos,” Ph.D. Thesis. Universidade Federal do Rio Grande, Rio Grande do Sul, unpublished, 2009.
 R. Allan, J. Lindesay and D. Parker, “El Ni?o Southern Oscillation and Climate Variability,” National Library of Australia Cataloguing-in-Publication Entry, Canberra, 1996.
 A. M. Grimm, S. E. T. Ferraz and G. Julio, “Precipitation Anomalies in Southern Brazil Associated with El Ni?o and La Ni?a Events,” American Meteorological Society, Vol. 11, No. 11, 1998, pp. 2863-2879.
 A. M. Grimm, V. R. Barros and M. E. Doyle, “Climate Variability in Southern South America Associated with El Ni?o and La Ni?a Events,” American Meteorological Society, Vol. 13, No. 1, 2000, pp. 35-57.
 M. D. Dettinger, D. S. Battisti, G. J. Mccabe, C. M. Bitz and R. D. Gerreaud, “Interhemispheric Effects of Inter-Annual and Decadal ENSO-Like Climate Variations on the Americas,” In: V. Markgref, Ed., Interhemispheric Linkages, Academic Press, London, 2001, pp. 1-16.
 E. M. Rasmusson, X. Wang and C. F. Ropelewski, “The Biennial Component of ENSO Variability,” Journal of Marine Systems, Vol. 1, No. 1-2, 1990, pp. 71-96.
 Y. Zhang, J. M. Wallace and D. S. Battisti, “ENSO-Like Interdecadal Variability: 1900-93,” Journal of Climate, Vol. 10, No. 5, 1997, pp. 1004-1020.
 A. Montecinos, A. Diaz and P. Aceituno, “Seasonal Diagnostic and Predictability of Rainfall in Subtropical South America Base on Tropical Pacific SST,” Journal of Climate, Vol. 13, No. 4, 2000, pp. 746-758.
 A. W. Robertson and C. R. Mechoso, “Interannual and Decadal Cycles in River Flows of Southeastern South America,” Journal of Climate, Vol. 11, No. 10, 1997, pp. 2570-2581.
 C. M. Krepper, N. O. Garcia and P. D. Jones, “Interan- nual Variability in the Uruguay River Basin,” Interna- tional Journal of Climatology, Vol. 23, No. 1, 2003, pp. 103-115. doi:10.1002/joc.853
 S. Hastenrath, L. C. De Castro and P. Aceituno, “The Southern Oscillation in the Tropical Atlantic Sector,” Contributions to Atmospheric Physics, Vol. 60, 1987, pp. 447-463.
 P. Aceituno, “On the Functioning of the Southern Oscillation in the South American Sector. Part I: Surface Climate,” Monthly Weather Review, Vol. 116, No. 3, 1988, pp. 505-524.
 R. G. Wagner, “Decadal-Scale Trends in Mechanisms Controlling Meridional Sea Surface Temperature Gradients in the Tropical Atlantic,” Journal of Geophysical Research, Vol. 101, No. C7, 1996, pp. 16683-16694.
 J. Nogués-Paegle and K. C. Mo, “Alternating Wet and Dry Conditions over South America during Summer,” Monthly Weather Review, Vol. 125, No. 2, 1997, pp. 279-291.
 J. L. Genta, G. Perez-Iribarren and C. R. Mechoso, “A Recent Increasing Trend in the Streamflow of Rivers in Southeastern South America,” Journal of Climate, Vol. 11, No. 11, 1997, pp. 2858-2862.