Using stable isotopes to construct food web models on the Truckee River

The construction of eight food web models using stable carbon and nitrogen isotopes was completed on the Truckee River. Seven primary sites were sampled for periphyton, macroinvertebrates, and fish in March and August 2003 and 2004. Food web models for March and August were then constructed for four site groupings. The models were constructed in Excel with base signatures that included measured periphyton signatures and calculated signatures for detritus and seston. The pseudo-optimization function in Excel's Solver was used to minimize deviations between predicted and observed stable isotope signatures while simultaneously solving for diet proportions of all food web species, and estimating carbon and nitrogen isotope trophic enrichment factors. Models such as these may ultimately aid in bioassessment by helping to determine how the food web within a river will change as species are introduced or eliminated or as carbon and nitrogen sources change due to anthropogenic impacts.