Predicting the Responses of Water Chemistry, Periphyton, Invertebrates, and Fishes to Salmon Recolonization Using Experimental Streams

Research indicating that salmon carcasses support the productivity and biodiversity of aquatic and riparian ecosystems has been conducted over a variety of spatial and temporal scales. For example, in some studies carcasses were manipulated in a single pulse or loading rate and manipulations occurred during summer or early fall rather than simulating the natural dynamic of an extended spawning period, a gradient of loading rates, or testing carcass effects in late fall-early winter when some salmon stocks in the US PNW spawn. To address these discrepancies, we manipulated salmon carcass biomass in 16 experimental channels located in the floodplain of the Cedar River, WA, USA between mid-September and mid-December, 2006. Total carcass loads ranged from 0 – 4.0 kg/m² (0, 0.001, 0.01, 0.1, 0.5, 1.0, 2.0 and 4.0 kg/m², n = 2 per treatment) and were added to mimic the temporal dynamic of an extended spawning period. We found little evidence that carcasses influenced primary producer biomass or fish growth; however nutrients and some primary consumer populations increased with loading rate. The ecological effects of carcasses varied across trophic levels and through time. We hypothesize that the variable effects of carcasses were a result of ambient abiotic conditions that constrained productivity and experimental conditions.  Despite these limitations, our study showed that carcasses could increase the trophic productivity of these experimental stream food webs during fall. Moreover, we observed that peak responses for primary producers and consumers occurred at a loading rate of ~1.0 – 2.0 kg/m², which was qualitatively similar to other experimental studies conducted during summer.