Kinetics of aerobic decomposition in the leaching phase of allochthonous plant detritus

Abstract

AIMS: This study aimed to evaluate, through an experiment with short sampling intervals, (1) the effects of detritus quality on dissolved oxygen (DO) consumption, on dissolved inorganic carbon (DIC) formation and on the stoichiometric ratio between the DO consumed and mineralized carbon (O/C ratio) during leaching of plant detritus in the early decomposition; (2) the temporal variation of the variables mentioned above according to changes in the quality of each detritus over time. METHODS: The detritus of leaves, branches and litter (3 g) previously dried were incubated in decomposition chambers containing 1 L of inoculum. The chambers were maintained at 24 ± 2 °C in aerobic condition. The DO concentrations dissolved organic carbon (DOC) and DIC were evaluated. The consumption of DO was adjusted to a first-order kinetic model. The hourly rates of DO consumption, DIC production and O/C ratios were determined. RESULTS: The DO consumption (2.62 mg.g-1) and DIC production (1.20 mg.g-1) were higher in leaves decomposition, and smaller in litter (1.50 and 0.42 mg.g-1, respectively). Inversely, the O/C ratio was higher in the decomposition of litter (3.56). The rates of DO consumption (0.50 mg.g-1.h-1) and DIC production (0.41 mg.g-1.h-1) were greatest in the early decomposition of leaves. CONCLUSIONS: Short sampling intervals are key to understanding the dynamics of decomposition in the leaching phase. Higher consumption of DO in leaves decomposition indicated a higher content of labile compounds in this detritus. The highest O/C ratios in the litter decomposition can be attributed to its higher content of refractory substances. Variations in DO consumption rates and in O/C ratios over time suggest that the leachate is heterogeneous, comprising labile and refractory fractions, analogous to the detritus as a whole. In terms of water quality alterations, leaves constituted the most critical resource and the litter presented less pronounced effects.