Oxygen uptake during mineralization of humic substances from Infernão Lagoon (São Paulo, Brazil)

Abstract

Assays were carried out to evaluate the dissolved oxygen uptake resulting from mineralization of humic substances (fulvic acid (FA) and humic acid (HA)) from different sources: sediment, dissolved organic matter (DOM) of 120-day decomposed aquatic macrophyte (Scirpus cubensis and Cabomba piauhyensis), and lagoon DOM. The experiments were also aimed at estimating the oxygen uptake coefficient of the mineralization. About 20-30 mg of substrate were added to 1.1 liters of water from Infernão Lagoon (21 degrees 33' to 21 degrees 37'S; 47 degrees 45' to 47 degrees 51'W). The solutions were aerated and the dissolved oxygen (DO) was monitored during 40 days. Dissolved organic carbon (DOC) and particulate organic carbon (POC) were estimated after 80 days of the experiment. Anaerobic processes were avoided by aerating the solutions. The results were fitted to a first-order kinetics model, from which the uptake of oxygen parameters was obtained. Oxygen consumption (OC) ranged from 4.24 mg L(-1) (HA--S. cubensis) to 33.76 mg L(-1) (FA--sediment). The highest deoxygenation coefficient (kD) was observed during mineralization of FA--DOM (0.299 day(-1)), followed in decreasing order by FA--S. cubensis, HA--sediment, HA--S. cubensis, FA --sediment, and FA--C. piauhyensis (0.282; 0.255; 0.178; 0.130, and 0.123 day(-1), respectively). The carbon analyses indicated that the FA and HA samples at the end of the experiment presented a decay that varied from 15.23% to 42.35% and that the FA and HA conversions into POC were relatively low (from 0.76% to 3.94%).

Effects of wind-induced sediment resuspension on distribution and morphological traits of aquatic weeds in shallow lakes

“…This budget lacks, however, of the assessment of the carbon release due to respiration processes in dense vegetated stands at the lake scale. A definitive assessment of the net ecosystem metabolism would take into account the quota of carbon decomposed and released in situ at the senescence of the plants, that having potential cascading effects on local oxygenation and on the enhancement of anaerobic processes such as methanogenesis (Cunha-Santino and Bianchini, 2004;Carvalho et al, 2005;Urban et al, 2009;Ribaudo et al, 2014).…”