Macroinvertebrates

Macroinvertebrates (animals without backbones that are visible to the naked eye) are well suited for monitoring studies because they are abundant and diverse and relatively easy to sample and analyze.  In most streams, the macroinvertebrate community is dominated by larval insects.  In this stage of development, insects live a completely aquatic existence feeding voraciously on organic matter and other invertebrates.  Each insect group has specific requirements for food, substrate, temperature, and dissolved oxygen concentrations.  The presence (or absence) of particular insects is, therefore, indicative of certain water quality and habitat conditions.

Inletkeeper Strategies

In Fall 2002, the lower Kenai Peninsula experienced two, 100-year flood events.  Major habitat alteration reshaped salmon stream channels and riparian habitat especially in the lower reaches of the Anchor River and Deep Creek.  In order to track the biological communities in these streams and to understand flood effects on stream productivity, Inletkeeper expanded its bioassessment program in the summer of 2003 to include sampling on all four salmon streams using University of Alaska Anchorage, Environment and Natural Resources Institute’s (ENRI) technical-level methods.

Inletkeeper collects samples in June and August annually to compare with pre-flood samples collected by ENRI in 1997 and 1999. A downward trend in abundance values on the Anchor River and Deep Creek suggests a poor recovery pattern in stream productivity.  Kicknets samples are considered semi-quantitative so the abundance values can not be expressed as a measure of density.  The trend is very consistent in both watersheds and the degree of change so great that the pattern is unlikely to be a sampling anomaly or a measure of natural variation, especially when different patterns are evident in the Ninilchik River and Stariski Creek.

The rate of recovery of macroinvertebrate communities after a flood event may depend on the severity of flooding, availability of refugia, and seasonal timing.  The two, 100-year flood events in October and November of 2002 were both severe and late in the season for quick recovery.  The extensive bank sloughing and channel widening on the Anchor River and Deep Creek may have limited the availability of refugia. On Beaver Creek, much higher up in the Anchor River watershed, the recovery pattern is more typical and, with an increase in Fine Sediment Biotic Index scores, suggests a positive flood effect of moving sediment out of the stream bottom.

Future Work

Cook Inletkeeper will continue its macroinvertebrate monitoring to assess if the recovery patterns seen thus far persist. Inletkeeper will work with the Project’s Technical Advisory Committee to develop a strategy to:

1. flush out the seasonal patterns seen in the Anchor River,
2. provide a better density measure of macroinvertebrates,
3. determine the need to improve the taxonomic level of identification, and
4. incorporate other measures of stream productivity.

Discussions with local researchers and resource managers will continue to consider if

1. recovery to pre-flood levels may be an unrealistic expectation in watersheds that are undergoing large-scale changes such as climate change and forest death,
2. salmon productivity would be expected to respond to decreasing macroinvertebrate densities,
3. ocean productivity patterns will damped out those seen in coastal watersheds for anadromous species, and
4. resident fish populations are being monitored closely enough to track freshwater productivity trends.

Additional Resources & Links

Environment and Natural Resource Institute (ENRI) at the University of Alaska Anchorage: http://aquatic.uaa.alaska.edu

Xerces Society:
http://www.xerces.org

Society for Freshwater Science (formerly North American Benthological Society):
http://www.freshwater-science.org/

EPA - Biological Assessment:
http://www.epa.gov/owow/monitoring/bioassess.html