The Temporal Variability of the Freshwater Discharge and Water Levels at the Patos Lagoon,Brazil

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.

Historic changes in flux of matter and nutrient budgets in the Bohai Sea

Over the past four periods （ 1959--1960, 1982--1983, 1992--1993, and 1998--1999）, the ecosystem of the Bohai Sea changed due to both a significant decrease of river water discharge from the Huanghe River and a reduction of precipitation. The shifts in nutrient chemistry could result in changes in the phytoplankton composition with an increased potential for non-diatom algal blooms. Simple box model was used to estimate the water - mass balance and nutrient budgets for the Bohai Sea. Water budgets indicate that the residual flow changed from out of the Bohai Sea before 1993, but became inflow to the Bohai Sea after then. The nutrient budgets developed indicate that the Bohai Sea was a sink for nutrients except for phosphate in 1959--1960 and 1982-- 1983 and for silicate in 1982--1983. Net water flow transports nutrients out of the Bohai Sea in 1959--1960, 1982--1983 and 1992--1993, but into the sea in 1998--1999 due to climate changes, such as precipitation and subsequent freshwater discharge. The residual fluxes of nutrients are minor relative to atmospheric deposition and riverine inputs. Conversions of phosphate values to carbon by stoichiometric ratios were used to predict that the system was net heterotrophic before 1982--1983 and net autotrophic after then. Nutrient budgets can explain the change of nutrient concentrations in the Bohai Sea except nitrates, which should include the surface runoff.

Prediction of salinity intrusion in the sheltered estuary of Terengganu River in Malaysia using 1-D empirical intrusion model

Generally one dimensional （l-D） empirical salinity intrusion model is limited to natural alluvial estuary. However, this study attempts to investigate its ability to model a sheltered alluvial estuary of the Terengganu River in Malaysia. The constructed breakwater at the mouth of the river shelters the estuary from direct influence of the open sea. The salinity density along the estuary was collected during the wet and dry seasons for scenarios before and after the constructed breakwater. Moreover, the freshwater discharges, tidal elevations and bathymetry data were also measured as model inputs. A good fit was demonstrated between simulated and observed variables, namely salinity distribution and intrusion length for both scenarios. Thus, the results show that 1-D empirical salinity model can be utilized for sheltered estuarine condition at the Terengganu Estuary, but with an appropriate determination of an initial point. Furthermore, it was observed that the salinity intrusion in the study area is largely dependent on the freshwater discharge rather than tidal elevation fluctuations. The scale of the salinity intrusion length in the study area is proportional to the river discharge of the -1/2 power. It was appeared that the two lines of the 1-D empirical salinity model and discharge power based equation fitted well to each other, with the average predicted minimum freshwater discharge of 150 m^3/s is going to be required to maintain acceptable salinity levels during high water slack （HWS） near the water intake station, which is located at 10.63 km from river mouth.

The Exchange Processes in the Patos Lagoon Estuarine Channel,Brazil

Investigation of process controlling the estuarine-shelf interaction in the Patos Lagoon estuarine channel is accessed using a two-dimensional numerical model. Results obtained suggest this approximation provides good precision level to investigate the advective transport of oceanic waters near the estuarine mouth. The introduction of coastal waters in synoptic time scales is dominated by advection in sub-superficial layers. This process results from the competition between flood currents driven by remote wind effects and gravitational circulation controlled by the intensity of the freshwater discharge. The short term exchange processes follow one most energetic cycle of 8 days and intense flood events occur during periods of low continental discharge and higher intensity winds. Very stratified salinity profiles are found during periods of moderated freshwater discharge. The salt transport is inversely related to the freshwater discharge intensity. It presents a mean rate of the 105 kg.day-1 transported landward during flood events.