August 2010 Article: An Evaluation of Qualitative Indexes of Physical Habitat Applied to Agricultural Streams in Ten U.S. States, by Robert M. Hughes, Alan T. Herlihy, and Philip R. Kaufmann
The diversity of metrics and methods for assessing physical habitat condition confounds comparisons among practitioners. Rapid qualitative indicators and assessments typically have higher sampling error and unknown bias, but time-intensive indicators limit the number of sites that can be sampled, all else being equal. This article presents a comparison of several popular indexes and concludes with some interesting observations on the roles of indexes and the need for more research.
The authors surveyed 51 previously sampled stream sites located in regions of row-crop agriculture in Oregon, California, North Dakota, South Dakota, Nebraska, Iowa, Minnesota, Pennsylvania, Maryland, and West Virginia to evaluate the comparability of four indexes of physical habitat condition relative to each other. The four indexes were: rapid bioassessment protocol (RBP); qualitative habitat evaluation index (QHEI); stream visual assessment protocol (SVAP); and qualitative physical habitat index (QTPH).
Their conclusion: “Despite varying perspectives of what ‘’habitat’’ is and the use of different metrics, these four qualitative physical habitat assessment protocols produced similar results. This suggests that if the goal is a rough estimate of overall physical habitat quality, the three wholly qualitative protocols are just as adequate as one based on multiple quantitative measurements of physical habitat (QTPH), which requires much more field effort. However, the highly significant correlations between macroinvertebrate biotic index scores and quantitative substrate metrics suggest that quantitative physical habitat measures may offer greater explanatory power than qualitative habitat assessments.” You’ll want to read the whole article before acting on this, because there obviously are a lot of qualifications.
The authors also note that protocols, indexes, and scoring criteria to suit natural regional and local differences and differing professional perspectives and management objectives hinder making national or regional assessments of stream habitat conditions in a consistent manner.
[Please note: I have quoted and paraphrased freely from the article, but the interpretation is my own!]