Diatom-based Multimetric Index of Disturbance
Organism-based indices have been a valuable monitoring tool in lotic waters and small lake systems, and have been commonly applied as fish and invertebrate indices. Algal indices, such as those using diatoms, are starting to be incorporated into routine monitoring assessments in the U.S.
Diatoms have become a widely-applied indicator group because they are taxonomically distinct, abundant in almost all aquatic environments, respond rapidly to changing conditions, and are well preserved in sediment deposits. Furthermore, evaluations of diatoms can provide a description of water quality that is not achievable from chemical analyses; the value of an integrative biological response can offset the inconsistency of rapid changes in water chemistries.
GLEI personnel developed a robust diatom-based model that uses quantified unimodal response coefficients of the species across environmental gradients. While this model will be of interest to Great Lakes managers and paleoecologists, it has some logistic constraints such as time and monetary dedication, taxonomic expertise, specialized software and a significant learning curve. Index approaches provide a more accessible choice for managers who may be considering the algae as an environmental quality indicator; they provide a means to evaluate environmental quality at a locale based on the diatom assemblage, and can be flexible enough to suit user groups with monetary or logistic limitations.
A diatom-based multimetric index to infer coastline disturbance was developed for Great Lakes coastal sites (Fig. 1). We defined 38 metrics based on autecological and functional properties of each species assemblage, including species diversity, percentages of motile, planktonic and dominant taxa, as well as taxonomic metrics (e.g., proportion of the genus Martyana or “Stephanodiscoid” taxa). Comparisons of individual metrics to watershed stressors revealed that many of the proposed metrics responded to human stressors, and so were considered for further development. Metrics that were redundant, or had no response to stressors, were excluded. The final multimetric index is a cumulative score – a sum of the important metrics, each weighted by the strength of their respective relationships to anthropogenic stress. While individually the metrics have relatively weak responses to stress, the multimetric approach provides a cumulative assessment of site quality. We anticipate future applications of this new index to monitoring programs and downcore analyses.