Defining stream integrity using biological indicators
2012-09
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Defining stream integrity using biological indicators
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2012-09
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Abstract
Biological indicators may offer the most comprehensive and accurate means to assess
the integrity of streams and rivers, as changes in a biological community represent an integrated
response to all environmental stressors present in an ecosystem. Biological indicators
are typically designed to quantify and=or summarize important aspects of either
ecosystem structure – the types and abundance of organisms found in a given habitat – or
ecosystem function – rates and patterns of ecological processes such as primary and secondary
production, nutrient cycling, and decomposition of organic matter. Increasingly,
resource managers use such indicators to assess whether surface waters fulfill the requirements
of their designated uses under the Clean Water Act.
Despite the recognition that biological indicators can aid management decisions, critical
questions remain regarding the best way to design, apply, and interpret them. In this
dissertation, I used a suite of statistical and empirical approaches to evaluate the design
and application of several different biological indicators of stream condition in various
contexts and scales across Minnesota. Specifically, I used a bootstrap approach, together
with a database of fish, macroinvertebrate, and environmental data collected by the Minnesota
Pollution Control Agency (MPCA) between 1996 and 2006 from approximately
1500 stream sites across Minnesota, to quantify variability associated with an Index of Biological
Integrity (IBI) developed by MPCA for fish communities in streams of two Minnesota
river basins. I placed this variability into a management context by comparing it to
impairment thresholds used in water quality determinations for Minnesota streams. I used
the same MPCA dataset to develop predictive taxa richness models for fish and macroinvertebrates
as additional indicators of the biological integrity of Minnesota streams, and
evaluated these models for sensitivity and precision. I further determined whether fish and
macroinvertebrate assemblages exhibited significant community concordance, and whether
significantly concordant communities yielded equivalent indications of stream integrity at
three nested spatial scales (statewide, ecoregion and catchment) in Minnesota. Finally,
I used data from the MPCA database to evaluate relationships between selected environmental
variables and the composition of fish and macroinvertebrate assemblages at all three spatial scales. I collected a second dataset of macroinvertebrate samples over the course of one year
(2010) from three agricultural streams in southern Minnesota to evaluate relationships
between structural and functional indicators of stream condition in response to a common
stream conservation practice (i.e., reach-scale restoration). Specifically, I examined
whether reach-scale restoration in disturbed agricultural streams in southern Minnesota was
associated with changes in (1) macroinvertebrate taxa richness, (2) seasonal variability in
macroinvertebrate community composition, and (3) secondary production (i.e., macroinvertebrate
biomass over time).
SUMMARY OF FINDINGS:
1. I found that 95% confidence intervals for IBIs scored on a 0-100 point scale ranged
as high as 40 points. However, on average, 90% of IBI scores calculated from
bootstrap replicate samples for a given stream site yielded the same impairment
status as the original IBI score. I suggest that sampling variability in IBI scores is related to both the number of fish and the number of rare taxa in a field collection. A
comparison of the effects of different scoring methods on IBI variability indicates
that a continuous scoring method may reduce the amount of bias in IBI scores.
2. Predictive taxa-loss models for fish and macroinvertebrates both distinguished
reference from non-reference sites. Predictive models for fish assemblages were less
sensitive and precise than models for invertebrate assemblages, likely because of a
relatively low number of common fish taxa. Significant concordance between fish
and invertebrate communities occurred at the statewide scale as well as in six of
seven ecoregions and 17 of 21 major catchments examined. However, concordance
was not consistently indicative of significant relationships between rates of fish and
invertebrate taxa loss at those same scales. Fish and invertebrate communities were
largely associated with different environmental variables, although the composition
of both communities was strongly correlated with stream size across all three scales.
3. I found no difference in macroinvertebrate taxa richness between restored and
unrestored reaches of agricultural streams in southern Minnesota. However, both
compositional similarity and secondary production were higher in restored reaches
relative to unrestored reaches, suggesting that reach-scale restoration may have
ecological effects beyond influences on diversity. These findings highlight the added
complexity conveyed by a consideration of functional, as well as structural,
indicators of stream condition. Higher productivity in the restored reaches was due largely to the disproportionate success of a small number of dominant taxa.
Secondary production estimates were considerably lower than those reported for
other similar-sized prairie streams; these low values may be indicative of stressful
conditions for biotic life in the study streams.
Description
University of Minnesota Ph.D. dissertation. September 2012. Major: Water Resources Science. Advisor: Bruce Vondracek. 1 computer file (PDF); xiii, 161 pages, appendices A-D.
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Dolph, Christine Laurie. (2012). Defining stream integrity using biological indicators. Retrieved from the University Digital Conservancy, https://hdl.handle.net/11299/141672.
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