Untitled

Abstract

In streams, particulate organic matter POM serves as a pivotal link between dissolved nutrients, microbes and organisms at higher trophic levels. Especially in forested streams, such linkage with allochthonous POM is fundamental for saprophytic chain of stream ecosystems. Here, we reviewed current understanding of riverine POM by focusing its classification, dynamics, and ecological role in streams. Generally, coarse particulate organic matter CPOM, 1 mm is broken down to fine particulate organic matter FPOM, 0.45 mm 1 mm and dissolved organic matter DOM, 0.45 mm while providing essential energy and nutrients for microbes and aquatic fauna. Since input and transport of POM depend highly on season and discharge fluctuation, POM concentration in temperate streams shows wide ranges: 0.001 to 3 mgC L 1 for CPOM and 0.05 to 1 mgC L 1 for FPOM. For deposited POM density, channel unit such as riffle and pool is also influential. Major ecological roles of riverine POM are 1 habitat for aquatic fauna, 2 energy and nutrient supply for microbes, 3 energy and nutrient supply for aquatic fauna, and 4 material transport to downstream reaches and ocean. Colonization of fungi and bacteria on POM mediates carbon and nutrient uptake of aquatic fauna, especially macroinvertebrates. In stream ecosystems, therefore, POM is a major driving force and repeatedly experiences biological interaction and transformation, which is referred as organic matter spiraling. Thus, understanding of organic matter dynamics and its biological interaction is essential for conservation and restoration of stream ecosystems.