Tracking Change in the Illinois River using Stable Isotopes in Modern and Ancient Fishes

Document Type


Publication Date

Fall 10-15-2016

Publication Title

River Research and Applications


Biological Sciences


The Illinois River has been heavily modified by human activities. We examined the nitrogen and carbon stable isotope composition of collagen from fish bones in two Native American middens comparing them to modern fishes in the River today. We also compared ancient and modern fishes to three reference samples – 1) Illinois River phytoplankton 2) backwater lake sediment and 3) tissue from riverside trees. We found a large increase in δ15N values in modern fish bone collagen relative to ancient collagen. However, there is little change in δ13C between ancient and modern samples. Bone collagen from invasive carp species (Hypopthalmichthys and Cyprinus) are similar to modern phytoplankton. All fishes are different from riverside trees and backwater lake sediment. The large shift in δ15N values between ancient and modern fishes is probably caused by contamination of the river by Chicago treated wastewater and by denitrified fertilizer run-off. Our results indicate a major change in nitrogen biogeochemistry in the modern river. Comparisons between ancient and modern δ13C values suggests little change in feeding behavior of fishes between ancient and modern times. However, our data for invasive carps suggest strong competition with native planktivores