Thin twigs decompose faster than thick ones under stagnant and flowing water: a double exponential decay model parameterization

The degradation of vegetation in the watershed and associated release of dissolved organic matter (DOM) and particulate organic matter (POM) can influence the water quality of new reservoirs. This study aimed to evaluate whether water velocity influences the degradation of twigs of different diameters that remain in the watershed of new reservoirs. The results of twigs degradation under flowing and stagnant water over time were fitted to a double exponential decay kinetic model, which presents the detritus as labile/soluble and refractory compounds. The model parameterization showed that labile fractions presented higher decomposition rates (KT) in flowing than, but there was not a clear trend in the comparison between the diameters in each water condition. On the contrary, the refractory fraction decomposition rates (kR) showed a clear pattern in all comparisons, showing higher values in flowing water and for thin twigs. These results showed that thinner twigs decompose more rapidly, due to the greater A:V ratio, and that the abrasive effect of water velocity promotes faster decomposition. In general, we observed that there was a pattern of increasing decomposition rates as the twigs decrease in diameter (9–10 mm < 5–6 mm < 2–3 mm) and from stagnant water to flowing water.