Figure 1.

Diagram of the experimental design, which included three trophic levels: basal resource (algae, bacteria, or tPOM), herbivorous zooplankton (Daphnia magna), and juvenile trout (Oncorhynchus mykiss). Treatments aimed to simulate the effects of eutrophication and browning on the nutritional quality of the lake food web, with treatments E and HE simulating eutrophication and BB and BT simulating browning. This was achieved by feeding herbivorous zooplankton from different basal resource cultures in varying proportions. Treatment E was the mix of algae of high (Cryptomonas ovata) and intermediate (Acutodesmus sp.) diet quality. HE contained solely intermediate quality algae (Acutodesmus). BB (browning with bacteria) was the mix of intermediate quality algae (Acutodesmus) and poor quality bacteria (Micrococcus luteus). BT (browning with terrestrial input) was the mix of intermediate quality algae and poor quality tPOM (the ground leaves of birch: Betula pendula). Daphnia raised on these diets we then fed to rainbow trout and compared to trout raised on commercial fish feed (optimal diet). Each treatment included four replicates. The ¹³C‐isotope‐labeling of Acutodesmus was used for determining transfer of individual molecules from diet to consumer. The contribution of any two diets (mean ± SD) in Daphnia was estimated using two source mixing model calculation based on ¹³C/¹²C (Table 4)