A simple and versatile technique for assessing cellulose decomposition potential in floodplain and riverine sediments

Abstract

Although cellulose decomposition potential (CDP) has been studied extensively in terrestrial ecosystems, particularly soils under varying land-uses, this process has received far less attention in running waters. As in soils, cellulose decomposition within the sediments of rivers and floodplains is also probably a critical pathway for carbon processing, especially given the amount of allochthonous organic matter entering these ecosystems. To test various hypotheses about CDP in floodplain and riverine sediments, we adopted the cotton-strip assay technique developed for estimating potential cellulose decomposition in soils. We incubated standard soil burial test fabric for varying periods of time in the sediments of three lotic ecosystems in France, Australia, and New Zealand. The extent of cellulose decomposition was measured as loss in tensile strength of a standard width of cotton strip. In floodplain sediments of the Rhone River near Lyon, CDP was least at sites with coarse sediments receiving down-welling surface water. Cellulose decomposition potential correlated significantly with sediment hydrolytic activity. In the riffles of three New Zealand gravel-bed stream reaches subjected to varying levels of sedimentation, heavy deposition of silt in up-welling zones reduced rates of cellulose decomposition but this was not evident in down-welling zones. CDP was always higher at the surface than 10-20 cm deep in the sediments. At two sites in a sub-tropical gravel-bed river in eastern Australia, macro-nutrient amendment enhanced cellulose decomposition in the hyporheic zones of central and lateral bars relative to controls without nutrients. Cheap, repeatable, versatile, and requiring minimum resources, this facile field method has the potential to provide the same insights into cellulose decomposition in aquatic ecosystems as it has in terrestrial environments. We consider its real utility lies in its value as a simple tool enabling comparisons of spatial and temporal changes in cellulose decomposition potential within and among sites in most aquatic environments.