Determining sources of organic matter (OM) to aquatic communities has been a central focus of aquatic ecology. In riverine ecosystems, spatial resource subsidies can occur among habitats within a river and between riverine and terrestrial ecosystems. This study examines OM sources in an arid river ecosystem, the Rio Grande/Rio Bravo del Norte (Texas). Fish, periphyton, vegetative detritus, and invertebrates were collected from 6 main stem and 9 tributary sites and analyzed for stable isotopes of nitrogen (N) and carbon (C). We utilized Bayesian mixing models (SIAR) to determine the percent contribution of C sources to fish consumers in food webs along an arid to semi-arid precipitation gradient.
Results/Conclusions
Results show that C sources supporting fish communities at mainstem sites were primarily from allochthonous (terrestrial) sources (percent allochthonous 49-79%). However, tributary sites exhibited a greater influence of autochthonous C (percent autochthonous 43-84%), but this influence varied. Differences in allochthonous versus autochthonous C sources in mainstem and tributary sites may be driven by higher turbidity in the mainstem sites. This study also suggests that, contrary to predictions, some arid riverine ecosystems may be supported by allochthonous C sources.