I'm an environmental scientist looking into dynamics of bacteria growth in river bed sediments. I collected lots of data, and used regression for most of the comparisons, but one (the most important) is giving me fits: I'm trying to figure out if bacteria have a habitat preference as it relates to sediment particle size (e.g., do bacteria like to live on fine clay particles, or do they prefer sand or gravel?)
Sediment samples were collected in 1000g glass "peanut butter" jars. Among other tests, the sediment was sampled for fecal bacteria and then run for grain size analysis. Here are the data types:
- Bacteria counts - reported as the number of colony-forming units per 100g of sediment (cfu/100g)
- Sediment grain size partition - grain size reported as a percentage of the whole sample, with 5 partitions (e.g., 10% gravel, 30% coarse sand, 25% med sand, 25% fine sand, 10% clay = 100% of sample)
What I really want to know is if bacteria counts can be explained by the prevalence of a certain grain size, or perhaps some "MiracleGro"-esque mix of the right proportions of all or some of the grain size classes. The latter of those two cases made simple regression messy, and probably isn't a valid test of the data. ANOVA may work, considering that "grain size partition" could be considered quasi-categorical. I just don't know if ANOVA is relevant, again considering that sediment grain size is several fractions of a whole that really have to be considered together.
Signed up for reddit just to ask this question, so that alone should describe my frustration/desperation. What statistical test is best suited for the situation?