10 - Bedsediments: Protein and POM content (RITRODAT-Lunz study area, Austria)

Summary

ABSTRACT The availability of organic matter to animal consumers is very dependent on its protein content. C/N relationships can therefore be used as food quality indicators, although C/N ratios are not only dependent on the actual protein content. The present study analyses the distribution in space and time of protein, TON and TOC in the bedsediments of a second order gravel stream (Oberer Seebach, RITRODAT – Lunz). All three parameters were measured in the same samples. The validity of C/N ratios as food quality indicators is confirmed for sample means but not for individual values.

INTRODUCTION

The energy basis of low order streams is mainly allochthonous organic matter. Above surface imports are bank run off and aerial drift. This organic matter must be processed by the microbial community to become available to animal consumers and the food quality depends on the intensity of microbial activity. The processing of the organic material takes place partly on the sediment surface and partly in the bedsediments. The bedsediments are defined as channel forming sediments quantitatively dominated by epigeic faunal elements (Bretschko, 1992). They are therefore the topmost layer of the hyporheic zone, the extent of which is usually not clearly defined (Bretschko & Moser, 1993; Schwörbel, 1961). The distributions of bacteria (Kasimir, 1990 and in press), meiofauna (Schmid-Araya, 1994) and macro fauna (Bretschko, 1981; Bretschko & Klemens, 1986) indicate a very high metabolic rate in the bedsediments. Organic matter is measured as total organic bound carbon (TOC) and nitrogen (TON). The spatial/temporal distribution of POM is known for a period of some years (Leichtfried, 1985; 1986; 1988; 1991a,b).