Macroinvertebrate and fish community response to a "2-stage ditch" reconstruction

Physically modified streams in agricultural areas usually have reduced “biotic integrity” due to reduced habitat value.  Often these streams also have lower chemical quality because of excessive nutrient inputs..   A “2-stage ditch” stream reconstruction has been proposed by hydrologists as a way to reduce the need to frequently dredge out channels in small agricultural streams.  Altering flow patterns during wet weather using the “2-stage” design may also have benefits to both physical habitat and water quality.

As part of a comprehensive chemical and biological assessment of potential benefits, we sampled fish and macroinvertebrate communities using a rapid bioassessment technique before and after a 2-stage ditch project in northern Indiana.  The sampling occurred on Shatto Ditch, an agricultural watershed of approximately 5 square miles.  Shatto Ditch flows into the Tippecanoe River, a high quality stream that supports several rare or endangered fish and mussel species.

Physical habitat in Shatto Ditch, as measured by the Ohio EPA QHEI technique, did not change after ditch reconstruction.  Fish community IBI (index of biotic integrity) scores increased marginally.  The greatest biological change following reconstruction was in the macroinvertebrate community.  Before the project, the isopod Lirceus fontinalis made up 95% of the community.  Following channel reconstruction, the number of isopods decreased drastically and snails, midges, odonates, and amphipods became much more abundant.  Unaltered areas of the stream were still dominated by isopods.  The benthic community changes were probably associated with reduced stream velocity during wet weather rather than water quality improvements.