The influence of macrozoobenthos in lake sediments

To investigate bioirrigation activity in Chironomus plumosus burrows of approximately 1.7 mm in diameter appropriate measurement techniques were developed. With the methods several parameters were measured for 4th stage of larvae: flow velocity (14.9 mm s-1), pumping time (33 min h-1), and pumping rate (61 ml h-1). It was shown, even in muddy lake sediments advection is a relevant transport process and should not be neglected. Rising temperatures result in increased pumping rates and increased influx rates of surface water into the sediment due to increased flow velocities in the burrows. Dropping oxygen concentrations prolong the pumping duration while the flow velocity decreases. Experiments show a seasonal variability of bioirrigation which is independent of constant laboratory conditions. Pore water species such as SRP are transported with the water flow into the overlying water body, whereas SO42- and O2 are transported from the overlying water into the sediment. Due to the oxidation of Fe2+, phosphorus is fixed into the sediment. The bioirrigation activity enhances the microbial abundance, changes the community structure, and increases the potential of enzymatic hydrolysis.