Fluxos de CO2 na interface ar-água do estuário do Rio Jaguaribe (CE)

Abstract

Human activities have caused an exponential increase in atmospheric concentrations of CO2, which is a current environmental concern because of its impact on future climate and on the oceans. The oceanic uptake of CO2 has to be assessed by observed flows between the oceanatmosphere surface layer. The measurement of such flows is through the parameter of partial pressure of CO2, which is a way of estimating the changes in the concentration of CO2 in the oceans. Other parameters, such as the total alkalinity, total carbon and pH, can be used to indirectly estimate the partial pressure of CO2 and its flows. This study quantified the partial pressure and the flows of CO2 emitted by the Jaguaribe River estuary (Ceará, Brazil) to the atmosphere, both directly and indirectly. The estuarine waters and the mangrove channels showed chlorophyll a concentrations ranging respectively between 0.95 – 2.25 μg.L-1 and 2.68 – 51.62 μg.L-1 . Phosphorus concentrations ranged from 0.027 – 0.138 μg.L-1 in the main channel and between 0.061 – 0.249 μg.L-1 in Cumbe channel. In general, the main channel was classified as ultra-oligotrophic, while the mangrove channel was classified as oligotrophic, mesotrophic and super-eutrophic depending on location and time of samples collection within the channel. The partial pressure of CO2 values obtained through the direct method ranged between 400.7 to 1694.1 μatm. The concentrations estimated by the indirect method ranged from 705.95 to 1927.16 μatm. The estuary was characterized as a source of CO2 to the atmosphere, emitting, on average, when comparing the two campaigns, of +142.02 ± 92.78 mmol.m-2 .d-1 . Its trophic state positively influenced the emission of CO2. The comparison between the results of partial pressure of CO2 obtained through direct and indirect methods, demonstrated a possible overestimation (> 49%) of the data by the indirect method corroborating other studies that have been conducted in estuarine areas. However, it is necessary to assess simultaneously the variability between the measurements in real time and the estimates of the flows for the certification of these results, because salinity and temperature changes obtained in different campaigns can contribute to this overestimation.