RELATING SETS OF VARIABLES IN ENVIRONMENTAL-STUDIES - THE SEDIMENT QUALITY TRIAD AS A PARADIGM

Many environmental studies generate multivariate data, often consisting of two or more conceptually different sets of variables. For example one may wish to relate species abundances to environmental variables. A recent concept gaining popularity in marine benthic impact studies is the ''sediment quality triad'', which relates benthic community composition as one set of variables to sediment chemistry (contaminents) as a second set, and to toxicities of sediment to test organisms in the laboratory as a third set. This is conceptually appealing, but the original applications of the concept rely heavily on indices (e.g. diversity indices, toxicity indices) rather than on multivariate statistics. Procedures for testing and describing relationships among variables are reviewed, with emphasis on environmental applications. We describe and exemplify several multivariate statistical approaches to effective application of the sediment quality triad concept, including Mantel's tests and related descriptive analyses; ordination on each set of variables followed by methods to relate ordination axes among the sets; canonical correlation analysis; fitting a general linear model; and cluster analysis on each set of variables followed by a three-way contingency table analysis.