Beneficial Use Impairment 6: Degradation of Benthos

The numbers, health, and diversity of macroinvertebrates inhabiting the stream beds in our watersheds are inseparable from the health of fish populations.

What the delisting guidance says -

In the riverine areas upstream from the lake affected waters (lacustuary or fresh water estuary), the average of the Invertebrate Community Index (ICI) values within the assessment unit do not significantly diverge from state biological criteria;

AND

In lake affected waters (lacustuary or fresh water estuary), the average of the L-ICI values do not diverge from state guidelines.

1Ohio EPA has determined the non-significant departure value for riverine ICIs to be 4 points and the targets presented in this table reflect the non-significant departure from Ohio WQS.
2Non-significant departure for the lacustuary ICI value has not yet been determined. A study is currently underway in to determine lacustuary criteria in Ohio. Once the study is complete, Ohio EPA will review the results and determine if the current target should be revised.
3Targets for Limited Resource Waters (LRW) are based on benchmarks as there are no criteria in Ohio WQS.
4 The ICI target for lacustuaries is based on an Ohio EPA study in 1994 that identified 34 as a value considered an attainable goal for the Lake Erie lacustuaries given the current altered habitat conditions in the absence of excessive sedimentation and water column enrichment or toxicity.

Note

  • Assessment units are the 12-digit Hydrologic Unit Code (HUC), Large River Assessment Unit (LRAU), or other agreed upon stream segment or subwatershed.
  • If waters have more than one designated use (i.e., Lacustuary and LRW or MWH), then the lowest target applies.
  • This BUI will not be evaluated for ICI in waters that are routinely dredged as it is unrealistic for a healthy benthos community to be restored under these conditions.

Progress toward delisting

Of the subwatersheds applicable, 61% of them, or 11 of the 18, are above the target scores for this BUI.

The HUC12s still not in attainment are areas of high development and waterway stress. The current Management Actions that have been identified and approved by the AOC Advisory Council and Ohio EPA will help improve the stream habitat and structure of the stream, in turn improving the benthos of the AOC.