River damming affects energy flow and food web structure: a case study from a subtropical large river

The river discontinuity caused by damming can modify both the availability of production sources and the energy flow in riverine food webs. We hypothesized the carbon source support food web would vary among the reaches in response to changing in hydrogeomorphic conditions, and this variability further caused food web structure changes. To test our hypothesis, three different river reaches in the lower Jinsha River, China, were selected and the stable isotope ratios of basal sources and dominant consumers were analyzed in three seasons 2015. The relative importance of basal sources showed temporal and spatial difference to varying degrees. Seston were the most important carbon sources in supporting all consumers and the contributions increased from upstream to downstream. Riparian C-3 plants played an important supplementary role in both reaches above the dam or only in the high flow period. Dam-induced flow alteration changed the trophic basis and the composition of food webs, resulting in a difference in the food web structures, and widening but with lowest complexity food web occurred in the downstream reach. The results further confirm that the differences in the hydrogeomorphologic conditions caused by dam construction can exert potential influence on riverine food web structures.