Stable isotope analysis and terrestrial index
Generally, seston samples were more depleted in deuterium, and thus had lower δ2H values compared to terrestrial insects (Appendix 2). Terrestrial index (i.e., the contribution of terrestrial resources to the diet of the consumer) was significantly higher for roach (Z = 16.25; P < 0.001; 0.60 ± 0.05), perch (Z = 7.71; P = 0.005; 0.86 ± 0.10), and bleak (Z = 21.39; P = < 0.001; 0.79 ± 0.13) caught upstream of the dam, compared with individuals of the respective species downstream of the dam (roach:0.40 ± 0.06, perch: 0.33 ± 0.07; bleak: 0.28 ± 0.12; Figure 4).