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.
Highlights
The direct influence of freshwater discharge along the coastal regions is observed in physical, chemical and geological processes [1-5, among others]
The Southern Oscillation Index (SOI) is used in order to investigate the relationship between the occurrence of the natural phenomenon El Niño Southern Oscillation (ENSO) and the non stationary anomalies observed in the freshwater discharge of the Patos Lagoon
Previous studies showed that coastal lagoons are dynamically driven by winds [23], especially when their principal axes are oriented in its dominant direction [24]
Summary
The direct influence of freshwater discharge along the coastal regions is observed in physical, chemical and geological processes [1-5, among others] This affects the primary production stimulating the benthic re-mineralization and creating spatial patterns of production associated with the high availability of suspended matter and intense turbidity of continental waters. The intensity and temporal variability of the freshwater discharge control the water quality changing quantities and the composition of organic and inorganic properties changing the residence time of materials [6,7,8] This influence is still observed controlling the residual circulation inducing spatial and temporal patterns of circulation reflected in transportation processes and stratification of the water column [9,10]. The Patos Lagoon and the adjacent continental shelf are freshwater influenced regions and some numerical modeling studies considering dynamic aspects with high resolution in space and time are presented by: [15,16,17,18]. [16] studied the physical forcing controlling the formation and behavior of the Patos Lagoon plume based on a three-dimensional hydrodynamic numerical model. [17] investigated the importance of straining and advection for the stratification evolution inside the Patos Lagoon coastal plume for each of its known physical modes using potential energy anomaly budgets. [18] investigated the contribution of the Patos Lagoon coastal plume to the deposition pattern along the inner continental shelf providing estimates of estuarine-shelf suspended sediment exchange. [15] investigated the importance of straining and advection for the stratification evolution associated with the wind driven circulation along the Patos Lagoon estuarine region
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