Growth Dynamics of Floating Typha Mats: Seasonal Translocation and Internal Deposition of Organic Material

The rate of organic matter deposition by Typha components to floating mats was determined using a method designed to minimize errors caused by seasonal translocation of dry mass among the living Typha organs. The estimated ash-free dry mass added by components within the mat (233 g m-2 yr -) included approximately equal quantities of material added by roots, rhizomes, shoots and shoot bases. The composition of these components in the organic material was consistent with the hypothesis that mats grow mainly from within, by internal deposition of belowground organs, rather than by accumulation of aerial shoot material at the mat surface. The estimated rate of vertical thickness increase of the Typha mats in the absence of decomposition was 58 mm yr-'. The dry mass of organic material that has accumulated (24 kg m-2) is >100 times higher than the estimated annual deposition rate, suggesting that the rate of anaerobic decomposition has been low (<1%).