Testing the effect of Limnodrilus sp. (Oligochaeta, Tubificidae) on organic matter and nutrient processing in the hyporheic zone: a microcosm method

Abstract

A set of slow filtration columns was developed to test the effect of macrofauna on hyporheic zone functioning. In a first step, the suitability of the experimental system was tested by measuring the variability in water flux, sediment redistribution, dissolved oxygen, number of ETS-active bacteria, and number of bacteria among columns. The results indicated a low variability between columns filled with heterogeneous sand-gravel sediments and without macrofauna. In a second step, the effect of the tubificid worm Limnodrilus sp. on organic matter and nutrient processing was investigated in experimental conditions. Physicochemical parameters (pH, specific conductance, dissolved oxygen, dissolved organic carbon, ammonium, nitrite, and nitrate contents) and microbial parameters (number of ETS-active bacteria, number of bacteria, and hydrolytic activity) were measured at different depths and dates in four columns. A number of 100 individuals of Limnodrilus sp. was introduced into three of the four columns whereas the last column without macrofauna served as a control. The test with oligochaetes demonstrated a stimulation of microbial activities at all depths. Tubificid worms tended to enhance nutrient and organic matter processing in the experimental system. These results suggest that tubificid worms play a specific role at the hyporheic interface due to their particular mode of feeding.