Investigation of the Composition and Origin of Particulate Organic Matter in a Forested River

Abstract

To generate information for better understanding of the occurrence and transportation of particulate organic matter (POM) in forested rivers, POM in both water and riverbed sediment phases of a forested river was collected from Oct. 2010 to Oct. 2011, and the composition and origin of POM were investigated. In addition, based on the concentration of POM and the discharge, the flux of the water phase POM was also computed. Particulate organic matter in both water and sediment phases was classified into three size fractions: large POM (> 16 mm), coarse POM (1-16 mm) and fine POM (1 μm-1 mm). The composition of these three fractions was further classified into allochthonous (leaves, twigs, herbs and soil organic matter) and autochthonous (green algae and biofilm). For the fine POM fraction that was too small to be classified by the eyes, analysis with a multi-source model enabled the clarification of its origin based on measurement of the carbon isotope ratio for both samples and end members. The obtained results revealed spatial and time variances in the concentration and the composition of all three POM fractions, with the fine POM being found to be the dominant constituent of the water phase POM. Less significant concentration differences among all three POM fractions in the sediment phase than in the water phase were also revealed. Large and coarse POM was found mainly consisted of such allochthonous species as fallen leaves and branches. For many fine POM samples, however, the percentages of the autochthonous species of green algae and biofilm were relatively larger.