Variáveis biogeoquímicas controladas pela maré em um estuário urbano: contraste entre condições de sizígia e quadratura

Abstract

The study aim was evaluate the temporal variability of materials fluxes between an urban estuary and coastal zone through Joatinga channel, which drains the Jacarepagua´s lagoon system, Rio de Janeiro. Several physical and chemical variables were monitored over 13 hours, at 1-hour intervals, in the water column. The samplings were made on a quarterly basis, seasonally, in neap and spring tides, totalizing eight campaings. Several variables were investigated: water temperature, salinity, pH, dissolved oxygen, transparency of the water, dissolved inorganic nutrients (NH4+, NO2-, NO3-, Si and PO43-), particulate nitrogen, chlorophyll a, total organic carbon in dissolved and particulated forms, suspended matter, currents intensity and direction. Non-parametric statistical test made it possible to assess the effects of seasonality and tidal conditions on the selected variables and the influence of the different environmental forcing, for example: hydrodynamics, rainfall and temperature. According to the results it was possible to consider the channel as an eutrophic environment, at least for the period in question, with higher fluxes between summer and spring of chlorophyll a (1.4 at 116.0 kg 13h-1) and NH4+ (37.8 at 17,772 kg 13h-1), in addition to an important load of suspended particulate matter (48.22 ton. 13h-1 in winter in spring tide), dissolved organic carbon 8.81 ton 13 h-1 and particulate organic carbon 3.03 ton. 13 h-1 in summer (neap tide). Furthermore, the evaluation of the physical data such as current speed and salinity allowed to classify the type of estuary as well mixed in the all spring tides sampling and strong stratification in summer and spring periods in neap tide. The final balance of the channel was generally influenced by synoptic events, it was concluded that the Joatinga channel is an environment mostly driven by tidal. Materials mass balance through the point studied revealed an exportation of all constituents, highlighting its importance in fertilization the coastal environment adjacent to it.