Shifts in caddisfly species composition in Sacramento River invertebrate communities in the presence of heavy metal contamination.

Abstract

The results reported in the study document a change in invertebrate species composition that may be due to exposure to increasing levels of toxic metals in the environment. This is a gradual response which could only be documented because of the long-term and extensive data base accumulated over 18 years. The study is unique in this respect and may also reveal an example of the unexpected side benefits which accrue from a monitoring program such as this. The study area was the upper Sacramento River, which extends from near Anderson, California, to the vicinity of Red Bluff, California. During a routine program conducted to monitor resident benthic invertebrate communities, unusual shifts in species composition of two indigenous caddisfly larvae were observed. These occurrences were not associated with any point source, nonpoint source, or seasonal event for which data were available. However, there is reason to suspect that heavy metals in this ecosystem had a role in the changes seen.