The information presented here has not been reviewed and is considered a DRAFT.

Below are the combined summary reports presented to the OEPA describing the metrics effectiveness, how well it meets its assumptions, and its statistical properties.

Summary

•  This was a successful trial for the Lake Erie benthic diatom metric (BDM). This trial demonstrated the effectiveness of the BDM to identify with fine gain resolution the health of the diatom assemblages as defined by their sensitivity to pollution. This is a valuable tool for the Ohio Environmental Protection Agency’s effort to monitor the nearshore environmental quality, understand nearshore biological dynamics, and diagnose anthropogenic impacts. Its use is highly recommended.

• Total phosphorus (TP) and total suspended solids (TSS) are the variables measured in this study that have the strongest influence in determining the composition of the diatom assemblages in these systems.

• The Lake Erie benthic diatom metric (BDM)has a moderately strong significant response to water chemistry variables measured in this study that are important anthropogenic impacts affecting the nearshore diatom assemblages.

• The BMD is efficient and flexible. Only three of 75 samples collected and analyzed from a wide variety of conditions and habitats in this study contained insufficient numbers of diatom valves for analysis.

• The BDM provides a convenient way to rank sampled habitats with a simple easily communicated number.

• Though metric precision was not established in this study, the BDM appears to have reasonably low method error.

• Time and expense of collection and analysis of BDM samples should be comparable to that of IBI and ICI analysis currently in use by the Ohio Environmental Protection Agency for stream assessments.

• There is scant historical record of nearshore diatom assemblages, but if used as a regular monitoring protocol the BDM will provide an understanding of biological dynamics and trends in the nearshore.

• Some new, important, and possibly invasive diatom species are reported in this study.

 

This study confirmed the reliability and effectiveness of the benthic diatom metric (BDM) to determine with fine grain resolution the health of the diatom assemblages as defined by their sensitivity to pollution. This can be a valuable tool for the Ohio Environmental Protection Agency’s (OEPA) effort to monitor the nearshore environmental quality, understand nearshore biological dynamics, and diagnose anthropogenic impacts. Its use is highly recommended.

This study tests the underpinning assumptions of the metric andevaluates its statistical properties. It also provides information on interpreting and using the metric.

The Metric Meets All of Its Important Assumptions

• Assumption 1) Total phosphorus (TP) is an ecologically important determinant of species distribution in the Lake Erie nearshore. The multivariate analyses used in this study provided evidence that TP was an important driver of the diatom assemblages and the BDM was measuring these effects. This study demonstrated a good correlation between the metric scores and TP.

 

• Assumption 2) the effect of secondary environmental variables is negligible or their co-variation with TP is constant in space and time. The evidence that metric scores were tracking diatom assemblage response to TP in the nearshore was confounded by total suspended solids (TSS) and the analyses were not able to conclusively separate the effects of TP and TSS. However, these variables appear to co-vary.

 

• Assumption 3) the samples collected from the Lake Erie nearshore reflect the original training set upon which the BDM is based.The correlation structure of the Lake Erie nearshore resembled that of the training set from which the metric was derived. One hundred ninety-seven (37%) of the taxa in the study had indicator values. TP explained significant variation in 15 (60%) of the 25 most common species.

 

Statistical Properties Affirm the Metric’s Effectiveness

• The metric had significant correlation with total phosphorus (TP) using a simple linear regression analysis.
• The metric could significantly detect changes in the diatom community as affected by TP concentrations over five water quality categories.
• The analysis suggests that seasons do not greatly affect scores. There is no limit on when the metric can be used.
• Location within an estuary affected metric scores with a general pattern of scores increasing inversely with river mile as a result of cleaner lake water mixing with more nutrient laden river water.
• Power analysis calculated for four pairs of replicate samples indicated three to twelve samples would be needed for a two tailed t-test with α = .05.
• The metric scores meet ordinary least squares assumptions and can be used for hypothesis testing such as t-tests, ANOVA, and regression analyses.