Characterization of dissolved inorganic carbon and dissolved oxygen in two impacted Amazonian lakes.

Abstract

Six surface water campaigns were carried out in lakes Bolonha-LB and Água Preta-LAP (Brazil) during 2018 -2019. Temporal and spatial variations of temperature, pH, electrical conductivity, dissolved oxygen (DO), total alkalinity (TA), turbidity, dissolved carbon dioxide (CO2aq), and partial pressure of CO2 (pCO2) were analyzed and estimated. High levels of CO2aq were observed during the study (104 -998 μmol l -1 ), while CO2eq in equilibrium with the atmosphere ranged between 11.5 and 12.3 μmol l -1 . The pCO2 values ranged from 3,400 to 23,600 μatm. DO ranged from 1.0 -8.5 mg l -1 and showed significant spatial differences (p < 0.05) between the lakes studied. Apparent oxygen utilization (AOU) showed positive values in 98.5% of the samples collected, indicative of heterotrophic processes (respiration > production). The analysis of the relationships between AOU and excess CO2 indicated that about 65% of the carbon mineralization in the lakes is anaerobic, indicating the predominance of the respiration process in the systems studied. A comparative analysis with other 117 tropical lakes showed that LAP and LB are part of the 78% of lakes with CO2 supersaturation. This work showed that: the heterotrophic processes identified during this study are mainly a product of the inorganic contributions of organic matter from the adjacent urban region.