The importance of excretion by Chironomus larvae on the internal loads of nitrogen and phosphorus in a small eutrophic urban reservoir

Measurements of ammonium and phosphate excretion by the Chironomus larvae were conducted in order to evaluate the importance of these chironomids for the internal loads of a small eutrophic urban reservoir. Ammonium and phosphate excretion rates by Chironomus larvae of small size (6-10 mm total length) were significantly higher than those of the Chironomids having medium (9-11 mm) and large (11-16 mm) sizes. A dependence in relation to temperature was recorded for the ammonium and phosphate excretions that was significantly higher at 25 °C than at 20 and 15 °C. Through a linear relation between biomass (dry weight) and total length and, between excretion and biomass and, data on chironomids densities, after an intense sampling in 33 sites distributed all along the reservoir bottom, the mean phosphate and ammonium excretion rates corresponded to 2,014 ± 5,134 µg.m-2/day and 1,643 ± 3,974 µg.m-2/day, respectively. Considering the mean biomass (34 mg.m-2) of Chironomus, the lake area (88,156 m²) and the mean excretion rates, the contribution of benthic chironomids to the internal loads would be 181 KgP and 147 KgN. for the sampling months (October-November 1998). These values showed that the internal loads by excretion from Chironomus larvae correspond to approximately 33% of the external loads of phosphorus in the lake and, in the case of nitrogen, to only 5%

Bioturbation of sediments by benthic macroinvertebrates and fish and its implication for pond ecosystems: a review

Bioturbation of bottom sediments at the sediment–water interface is currently gaining more attention in studies dealing with the functioning of aquatic ecosystems. Such bioturbation can be caused by a variety of benthic macroinvertebrates or benthivorous fish that forage and burrow various bottom tubes, holes and pits. Thus, the processes involved may either be a result of direct interception by benthic animals, e.g., through bioresuspension of particles or through food ingestion and biodeposition, or of other indirect effects, e.g., changes in the physical properties of sediments or through the constructions mentioned above, along with corresponding changes in pond ecosystem functioning. The most distinct effect of benthivorous fish bioturbation activities is an increase in the turbidity of the water, which can lead to many subsequent knock-on effects, including inhibition of phytoplankton and submersed macrophyte growth with resulting alterations in physico-chemical water conditions. The importance of benthic macroinvertebrates and fish in bioturbation processes is also indicated by an increase in the numbers of resting cyanobacterial colonies recruited due to bioturbation of bottom sediments