Stream foodweb δ13C and geomorphology are tightly coupled in mountain drainages of northern Idaho

The relative influence of landscape vs local processes on variation in stream C and energy sources to lotic consumers remains unresolved, but is a key component in understanding pathways through stream food webs. I investigated potential linkages between the distribution of delta C-13 signatures of primary producers (periphyton), terrestrial organic matter (detritus), and secondary consumers (aquatic invertebrates and fish) and: 1) drainage area and 2) stream reach geomorphology in 3 mountain watersheds of northern Idaho, USA. When considered alone, drainage area explained variation in the delta C-13 signatures of periphyton (R-2 = 0.30) and sculpin (R-2 = 0.15) only. Subsequent General Linear Models (GLMs) showed that stream morphology explained significant variation in delta C-13 of periphyton (79%), Diptera (93%), sculpin (51%), and trout (63%). Drainage area was not significant in these models, a result indicating that once delta C-13 signatures are explained as a function of geomorphic type, the contribution of drainage area becomes less important. On the whole, consumer delta C-13 signatures related more strongly to periphyton delta C-13 than detrital delta C-13, though this relationship varied among geomorphic types. Collectively, results indicate that the morphology of a stream reach (including factors such as substrate size and storage elements, floodplain development, etc.) may be an important factor in the assimilation and distribution of C in food webs in forested mountain streams.