Limnetica 33

This study assessed riparian vegetation as a source of energy in different ponds. The trophic importance of food sources from the riparian zones for invertebrate consumers was analysed using the dual stable isotope technique. We measured stable carbon (δ¹³C) and nitrogen (δ¹⁵N) isotope values for three energy sources and primary consumers in four ponds in NW Spain to determine food sources that support primary consumers. Samples of littoral macroinvertebrates, macrophytes, epiphyton, and riparian vegetation were collected during two periods (summer 2010 and summer 2011) at each site. We used the MixSIR Bayesian mixing model to model the contribution of potential food sources of organic carbon supporting primary consumers at the study sites. The δ¹³C signatures of food sources varied between -35.5 ‰ and -20.76 ‰, whereas the δ¹⁵N signatures ranged from -6.2 ‰ to 11.27 ‰. Primary consumer isotope signatures corrected for the discrimination factor were within the range of the isotope values of the potential food sources in three of the ponds. Significant differences were observed in δ¹³C and δ¹⁵N signatures among sources at each site and overall (p < 0.05). Significant differences were also found among sampling sites for each source separately and for overall food sources (p < 0.05). The MixSIR Bayesian stable isotope mixing model indicated that riparian vegetation and epiphyton were the most important production sources supporting the biomass of invertebrates overall. In addition, riparian vegetation and epiphyton were, most likely, a food source in the three ponds. Macrophytes were an unlikely food source for invertebrates in all ponds, although they could have some importance as a source in the Bodeira pond.