Decomposition of Particulate Organic Carbon from Aquatic Macrophytes Under Different Nutrient Conditions

Abstract

This study compared the decomposition of particulate organic carbon (POC) of two macrophyte species under four nutrient conditions and its fate within the aquatic system. Samples of aquatic macrophytes and water were collected from Barra Bonita Reservoir (Sao Paulo State, Brazil). Dissolved organic matter was leached from the plant material. Incubations were prepared with POC, inoculums and water from the reservoir, simulating different nutrient concentrations with the same N:P ratio. POC was quantified, enzymatic activity was measured, and nutrient concentrations and fiber contents were analyzed. A kinetic model was adopted to explain and compare the carbon decay. The fitting of the kinetic model showed biphasic decay for both species, indicating two classes of compounds: a reactive organic resource and a recalcitrant resource. The reactive organic resource breakdown (k ROC = 0.1 day−1) generated a dissolved fraction, which was consumed according to detritus quality (Paspalum repens; k 3 = 0; Pistia stratiotes; k 3 ranging from 8 × 10−4 to 0.013 day−1). The slow mass loss of the recalcitrant resource is related to the high nutrient concentrations that improved enzymatic activity and fiber decay. The yields of the different routes of carbon POC derived depend on both detritus quality and environmental nutrient conditions.