Mineralisaton assays of some organic resources of aquatic systems

Abstract

Assays were carried out to evaluate the consumption of dissolved oxygen resulting from mineralisation processes in resources usually found in aquatic systems. They were also aimed at estimating the oxygen uptake rate of each investigated process. Experiments were conducted using substrates from 3 different places. A fixed amount of substrate was added to 5 litres of water from Lagoa do Infernão that was previously filtered with glass wool. After adding the substrates the bottles were aired and the amount of dissolved oxygen and the temperature were monitored for 55 days. The occurrence of anaerobic processes was avoided by reoxygenating the bottles. The experimental results were fitted to a first order kinetics model, from which the consumption of dissolved oxygen owing to mineralisation processes was obtained. The amount of oxygen uptake from the mineralisation processes appeared in the following decreasing order: Wolffia sp., Cabomba sp., Lemna sp., DOM (Dissolved Organic Matter), Salvinia sp., Scirpus cubensis, stem, Eichhornia azurea, sediment and humic compounds. The deoxygenation rates (day-1) were: 0.267 (humic compounds), 0.230 (Lemna sp.), 0.199 (E. azurea), 0.166 (S. cubensis), 0.132 (sediment), 0.126 (DOM), 0.093 (Cabomba sp.), 0.091 (stem), 0.079 (Salvinia sp. and Wolffia sp.). From these results, 2 groups of resources could be identified: the first one consists of detritus with higher amounts of labile (ready to use) compounds, which show a higher global oxygen uptake during the mineralisation process; the second one consists mainly of resources that show refracting characteristics. However, when the consumption rates are analysed it is noted that the mineralised parts of the refracting substrates can be easier to process than the labile fractions of the less refracting resources.

The effect of the size of particles on mineralization of Oxycaryum cubense (Poepp. & Kunth) Lye

“…1d). The temporal evolution of the consumption of DO obeys first order kinetics (Equations 1 and 2), similar to those obtained in long term BOD experiments (Bitar & Bianchini Jr., 2002). By matching the experimental data to Equations 1 and 2, one can infer that the oxidation of DOM from the Infernão lagoon generated a background oxygen consumption (OC max ) of 5.8 mg.L -1 (halftime (t 1/2 ) = 2.9 days) when the experiments were being done.…”

Oxygen demand during mineralization of aquatic macrophytes from an oxbow lake

“…The mean values of k d estimated from other studies on aerobic mineralization of aquatic plants (Cunha and Bianchini Jr., 1998;Lemos et al, 1998;Brum et al, 1999;Farjalla et al, 1999;Bitar and Bianchini Jr., 2002) were 0.180 per day (half-time = 26 days). This value indicates that, on average, the mineralization process for intact detritus was 5.8 times slower (variation from: 0.014 per day (E. najas) to 0.045 per day (C. furcata).…”

“…(Bitar and Bianchini Jr., 2002), Montrichardia arborescens (Cunha-Santino et al, 2004), Nymphaea ampla (Brum et al, 1999), Potamogeton stenostachys (Brum et al, 1999), Cabomba sp. (Bitar and Bianchini Jr., 2002), Salvinia sp. (Bitar and Bianchini Jr., 2002), Eichhornia azurea (Bitar and Bianchini Jr., 2002) and Typha domingensis .…”

“…(Bitar and Bianchini Jr., 2002), Salvinia sp. (Bitar and Bianchini Jr., 2002), Eichhornia azurea (Bitar and Bianchini Jr., 2002) and Typha domingensis . Other species also showed high values for OC max than obtained in the present study: Nymphaea ampla and Potamogeton stenostachys and Wolffia sp.…”

“…Other species also showed high values for OC max than obtained in the present study: Nymphaea ampla and Potamogeton stenostachys and Wolffia sp. (Bitar and Bianchini Jr., 2002). Regarding the mineralization of detritus, it has frequently been associated to the increments of the microorganisms metabolic acting on detritus, usually with high concentrations of nutrients (as DOM) and with low content of recalcitrant structures, such as lignin and cellulose (Gessner, 2000;Komínková et al, 2000).…”