Macroinvertebrates As Biological Indicators of Water Quality

Aquatic Biology Fall 2009 - 1 -

Macroinvertebrate Lab

The River Continuum Concept describes the fate of organic matter from headwater to delta, and the processes that affect this metabolism. The distribution of different types of organic matter determines the distribution of macroinvertebrates that process each type of organic matter. These processes apply broadly down the length of a large river system, but they also apply to microhabitats within a stream. The ratio of production to respiration (P/R) is not likely to differ greatly over a few meters’ distance within a stream but microhabitat will nevertheless have a strong influence on the types of invertebrates that occur there.

In this lab we placed gravel baskets in flowing and low-flowing areas of the Buffalo River. Area of high flow present ecological conditions typical of headwaters: steep gradient, fast water flow, and low silt deposition (FPOM and UFOM) and high DO. We may predict to find shredders (CPOM), scrapers (autochthonous OM), predators and a few collectors in these areas. In low- flowing areas of the Buffalo River there is a notable deposition of FPOM and UFOM and consequently higher BOD. Here, we expect to find mainly collectors and a few predators.

This is a gross generalization, but for the purposes of this lab we will assign ecological function (processing of OM) with these taxonomic groups:

Predators: Plecoptera, Coleoptera, Hemiptera, Odonata Shredders: Ephemeroptera Scrapers: Gastropoda Collectors: Trichoptera, Diptera (Chironomidae, Simuliidae, Tipulidae)

We will collect data from organisms attached to the gravel baskets you set out on Sept 1, 2009. After 4 weeks these rocks should be well colonized. Our first task is to classify macroinvertebrates into each ecological functional group and compare proportional representation of these groups between riffle and pool baskets.

Analysis We will have about 10 baskets from each habitat type which should hopefully provide sufficient statistical power to detect effects. To test for differences between habitat type we will use factorial ANOVA (ANalysis Of VAriance) using habitat type (S, P) and ecological functional group (P, SH, Sc, C) as categorical predictors. Because we will be using proportional data (i.e., not normally distributed) we will have to do an arcsine square root transformation (in Excel: =ASIN(SQRT(A2)). This ‘hocus pocus’ is standard procedure for rendering proportional data suitable for statistical analysis by parametric procedures such as ANOVA. The interaction term of the ANOVA will tell us if the representation of each functional group differed by habitat.