Robust parameters confirm predominance of heterotrophic processes in the plankton of a highly humic pond

The conclusions about the role of allochthonous organic matter in the food chains of inland waters are still often conflicting. Here we studied whether the results of specific experiments made in a small pond with very high concentration of allochthonous organic matter could be verified by simple, but robust, basic environmental parameters measured in the field. In summer primary production of phytoplankton could explain only ca. 20% of epilimnetic respiration and <10% of the nutritional requirements of zooplankton. These results agree with those of earlier experimental approaches and unequivocally suggest the major role played by allochthonous nutrition for the plankton in this pond. The roles played by photochemical degradation and anaerobic processes in the transformation of humic compounds available to epilimnetic food web in particular deserve further elucidation.