Ecology of juvenile salmon in upland vs. lowland Alaskan streams: An assessment of food webs using stable isotope analysis

Stable isotope analyses were used to track the food webs of 6 upland and 7 lowland coho salmon rearing streams in the Matanuska-Susitna Valley, Alaska. Wetland streams drain vast wetland systems and are characterized by slow moving water, silty substrate and are dominated by grass and shrub riparian vegetation. Upland streams drain snowmelt from mountains and are characterized by fast flow, gravel or cobble substrate, and are dominated by grass and tree riparian vegetation. CPOM, algae, and juvenile salmon samples were analyzed for carbon and nitrogen stable isotopes. These ratios were used to determine potential energy sources and energetic pathways from primary producer to juvenile salmon. Preliminary data from 2008 show significantly different δ¹³C signatures between upland and wetland sites, suggesting food webs have different energy sources. We hypothesize upland streams’ food webs will be autochthounously driven due to clear water conditions and be characterized by δ¹³C signatures similar to algae, whereas wetland streams will be fueled by allochthonous input due to tanic water and be characterized by δ¹³C signatures similar to CPOM.  The data also show similar δ¹⁵N signatures, suggesting juvenile salmon maintain a similar trophic position, regardless of site. 2009 data is currently being analyzed.