Use of δD and δ18 O to trace the origins and movements of macroinvertebrates in large river floodplain water bodies

Understanding energy and nutrient fluxes among floodplain water bodies and between rivers and their floodplains is essential for comprehending the dynamics of modern, altered river systems.  Aquatic invertebrates may move between floodplain and river habitats deliberately (through emergence and dispersal) or through passive transport during flooding, and these movements may represent significant fluxes of energy and nutrients.  We assessed the usefulness of stable isotopes of hydrogen and oxygen (D and ¹⁸O respectively) for identifying the origins and movements of macroinvertebrates in Mississippi River floodplain water bodies.  We sampled water and invertebrates from the Mississippi River channel, intermittent and permanent floodplain wetlands, and tributaries during 2007 and 2008. Results showed consistent relationships between δD and δ¹⁸O signatures in invertebrate tissues and their home water bodies.  We also investigated dietary effects on δD and δ¹⁸O and the persistence of isotopic signatures in invertebrates that were removed from their home waters and raised in growth chambers. Results indicate that hydrogen and oxygen stable isotopes can be useful tools for assessing the origins of floodplain invertebrates and quantifying the relative inputs of different habitat types in large river systems to main channel food webs.