Basal Carbon Sources Supporting Fish Food Webs in Terminal Basin Rivers

Abstract

Terminal basin rivers—those with no outlets to the sea—are unique systems that have been traditionally under-studied despite their widespread occurrence in drier regions of the world. The goal of this study was to elucidate the contributions of terminal basin rivers to broader concepts in lotic ecology using the contrasting frameworks of the River Continuum Concept (RCC) and the Riverine Ecosystem Synthesis (RES). Study sites were chosen for two rivers of the Great Basin, USA, according to coarse-scale hydrogeomorphic variables and included constricted-valley uplands, constricted-valley lowlands, wide-valley uplands, and wide-valley lowlands. Using amino acid, compound specific stable isotope analysis of amino acids (AA-CSIA) of carbon (C), we determined isotopic signatures for fish consumers and their potential food sources. AA-CSIA values for essential and conditionally essential amino acids were used as dietary tracers to estimate the proportional contribution of four different food groups: autochthonous resources (cyanobacteria and green algae), fungi, C3 plants, and C4/CAM plants to consumer basal diets using a Bayesian mixing model. Results suggest that consumer tissue of fish from all sites, regardless of site position along the river network, valley hydrogeomorphology, riparian vegetation, or fish species, was primarily derived from autochthonous C, with an average proportional contribution of 79.9±3.1%. This finding lends some support to the RES, in that over the entire river network, 50% of metazoan production was supported by autochthonous resources; however, there was no significant effect of hydrogeomorphology on the types of food sources assimilated. Additionally, we found no effect of site position to support the RCC. Future studies might gather additional data in different river systems.