Aerobic and anaerobic decomposition of Pistia stratiotes leachates from a tropical eutrophic reservoir (Barra Bonita, SP, Brazil)

I Bianchini Jr,Mb Cunha-Santino,Rs Panhota,Rh Silva

doi:10.1590/s1519-69842010000300012

I Bianchini Jr, Mb Cunha-Santino + Show 2 more

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https://doi.org/10.1590/s1519-69842010000300012

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Abstract

The present study discussed the kinetic aspects of leachate decomposition from an aquatic macrophyte, Pistia stratiotes L (water lettuce). This species was collected from Barra Bonita Reservoir located in the State of São Paulo (Brazil). Decomposition chambers were prepared with high molecular weight (HMW), low molecular weight (LMW) and integral (INT = HMW + LMW) dissolved organic matter (DOM) diluted with reservoir water. The samples were incubated at 20 degrees C, in darkness and under aerobic or anaerobic conditions. For 79 days, the concentrations of dissolved oxygen (DO) and organic carbon (OC) were measured. For calculating the deoxygenation coefficients (k d) and maximum oxygen consumption (COmax) the concentration of DO was integrated and fitted to a first-order kinetics model, which also applied to the depletion of OC concentrations. The COmax of INT incubations were 4% higher than the sum of HMW and LMW fractions. The deoxygenation coefficients, k d, had the same order of magnitude for all treatments. In relation to carbon decay, regardless of the availability of oxygen, the INT DOM also showed higher mineralisation. These results suggest that the leachate mineralisations are short-term processes; when the fractionation of the leachates occurs, the LMW had organic compounds with more accessibility for heterotrophic metabolism. On the other hand, when compared to INT DOM, the HMW and LMW were less consumed suggesting an interaction of the reactivity of the leachate. Our data suggest that in the Barra Bonita Reservoir the mineralisation of P. stratiotes leachates occurs through two competitive pathways (i.e. mineralisation of the labile compounds and formation of recalcitrant organic resources and their mineralisation) in which the oxygen availability and the molecular mass of DOM can interfere in the rates of reactions.

Highlights

In tropical aquatic systems macrophytes usually find favourable conditions for growth, being important for the carbon dynamics and cycles of nutrients (Wetzel, 1995)
The determination coefficients (r2) point to an adequate model using Equation 1 to describe the kinetics of oxygen consumption from dissolved organic matter (DOM) mineralisation
Based on a similar experiment that used DOM from Myriophyllum aquaticum and nitrapyrin (Nunes et al, 2007), we suppose that the later peaks of consumption in Figure 1 arose from oxidation of nitrogen compounds; in this case, we inferred that low molecular masses (LMM) DOM had a higher concentration of amine compounds

Summary

Introduction

In tropical aquatic systems macrophytes usually find favourable conditions for growth, being important for the carbon dynamics and cycles of nutrients (Wetzel, 1995). In addition to the chemical and physical interactions related with the DOM (e.g. light attenuation, sorption of dissolved constituents capacity; binding of xenobiotics) (Francko, 1990; Steinberger, 2003), this substance can represent a major carbon source for heterotrophic organisms, including bacteria, protozoa, and some algae. In this context, DOM usually comprises the main driving force for the microbial loop, promoting the growth of these microorganisms and the flux of carbon throughout the whole food web (Sigee, 2005). For determination of the chemical nature and dynamics of DOM, ultrafiltration techniques have been used to fractionate these compounds into different molecular masses (Hedges et al, 1994; Amon and Benner, 1996)

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