Extracellular enzyme activity within hyporheic sediments of a small lowland stream

The activity of extracellular α-glucosidase, β-glucosidase and β-xylosidase were measured in stream water, interstitial water and hyporheic sediments of a small lowland stream. Percent contribution of all the activity in the solution phase (<0.2 μm) to the total enzyme activity was low (15–40%), indicating that the enzyme activities are predominantly associated with bacterial cells. Generally, hyporheic sediments dominated the enzyme activity. Stream water, interstitial water and sediments showed activites that decreased in the order β-glucosidase>α-glucosidase>β-xylosidase. The fine fraction of the sediment (<0.063 mm) had much higher enzymatic activities than the coarser fraction (0.063–1 mm). All the extracellular enzymes, had higher activities during summer, period was attributed to the maximum input of allochthonous organic carbon into the sediments being at this time. A low ratio of α-glucosidase to β-glucosidase activity in the sediments, and no obvious spatial and seasonal changes in the ratio of β-xylosidase to β-glucosidase activity, suggested that cellulose is a predominant carbon source for hyporheic heterotrophic bacteria.