Stable Isotopes in Stream Food Webs

Stable isotope analysis has become a common tool for studying stream food webs and for testing hypotheses about stream ecosystem processes and stressors that may affect the structure of the food web or resources available to consumers. In this chapter, we provide a brief discussion of use of natural abundances of stable isotopes to study stream food webs, including a primer on stable isotope terminology, fractionation processes that govern differential cycling of stable isotopes of the same element, and some of the applications of the specific elements most often commonly used for stable isotope studies in stream ecosystems. Our objectives are to illustrate a generalized method (Basic Method) for characterizing and comparing stream food webs using δ¹³C and δ¹⁵N, and three more advanced experimental approaches (Advanced Methods 1-3) for examining specific questions or hypotheses about resource use in stream food webs using δ¹³C, δ¹⁵N, and δD.