Elizabeth,
My name is Melody Keena and I am a Research Entomologist working for the Forest Service in Hamden, CT. My web page is
https://www.nrs.fs.fed.us/people/mkeena. I read your report and thought your questions and general methods were good. You had issues that are common to field work. There is always something like ice or twisted lines that makes the study more difficult. The mix of insects and other invertebrates that you found was partly becasue of the time of the year that you dis your experiement. You might find it interesting to see how what you collect would change thoughout the year as water temperature changes. You made a very good observation that the surface area and amount of places to hide is influences by leaf size (You should have measured the leaves to be able to show a clear realationship graph leaf size vs number of invertebrates found and then add a linear trend line). Below are some thoughts on room for improvement in future studies.
When you set up a study it always has to have replication witin each treatment. So in your experiement you should have had a minimum of 3 bags at each location in the stream so that you could calculate the means and compare those. Since three locations would then be a lot of work you would need to decide if you just wanted to compare the different leaves at just one location.
When you present your methods make sure you tell the reader everything they would need to know to repeat the experiment. Also, when you present results tell the reader what the numbers and numbers in parentheses mean so they don't have to figure it out themselves.
To compare between sites or leaves you need to use statistics which look at the variation betweem the means and determine if it is big enough to be different. One way you can do that visually is show the mean and the standard error. Standard error is the standard deviation divided by the square root of the number of replications. If you want to go into science you will need to learn statisitcs so start now by reading about it.
You did not tell the reader how the biotic index was calculated. Assume the reader knows nothing.
When ecologists look at data like you collected they ask questions about species richness and abundance. You looked at abundance (total species found) but only touched the surface of richness (how many species are found).
