Improving Diatom Enumeration Methods For Use In Predictive Bioassessment Models
Tyree, Meredith A 1 ; Bishop, Ian W 2 ; Spaulding, Sarah A 3
1 Institute of Arctic and Alpine Research (INSTAAR), University of Colorado Boulder
2 Institute of Arctic and Alpine Research (INSTAAR), University of Colorado Boulder
3 United States Geological Survey, University of Colorado Boulder
An emerging trend in bioassessment is the application of models that predict species assemblages expected at sites in the absence of human impact. These observed/expected (O/E) models, however, have had limited success when applied to diatoms, perhaps because the models are not well-suited to the method traditionally used to characterize diatom communities (Cao et al. 2007). The traditional enumeration method prescribes that all valves be counted on a transect until a 600-valve count is reached. Dominance by one or two taxa is common in diatom samples and could be problematic for O/E models using this counting method, particularly because taxa that occur in less than 5% of sites are excluded from analysis (Zuellig et al. 2012). To address this problem, we analyzed the nature of diatom communities in reference sites and used our results to develop an alternative counting method that better consistently captures rare species. In our alternative method, the first 100 valves on a transect are enumerated, then the slide is scanned in non-overlapping transects for one hour, recording taxa only as presence/absence. We will next compare O/E models built on traditional counts to models built on alternative counts. If successful, our alternative method could improve measurements of stream health while expediting analyses and saving money.
Cao, Y., C. P. Hawkins, J. Olson, and M. A. Kosterman, 2007, Modeling natural environmental gradients improves the accuracy and precision of diatom-based indicators: Journal of the North American Benthological Society v. 26, p.566–585.
Zuellig, R. E., D. M. Carlisle, M. R. Meador, and M. Potapova, 2012, Variance partitioning of stream diatom, fish, and invertebrate indicators of biological condition: Freshwater Science v. 31, p.182–190.