When doesn't a watershed work?

OK, so everyone seems to be good with the concept that water moves downhill. But there's one thing I didn't mention, a key assumption we use when we take the watershed as our study unit, and it can throw a monkey wrench in the whole idea of a watershed boundary.

Today we got a first look underground - in the field digging in the soil - and way underground as Ivan Fernandez told us about bedrock and surficial geology.

That's the hint - can you figure out where we might be missing some water and leaking some of our study chemicals out of the watershed, without us even realizing?

What’s the deal with our rinse water?

This morning I said that I couldn’t mail the ultrapure or ‘mercury-free’ water from the lab up to Zen to sample, so instead I asked her to buy some bottles of Poland Spring (no endorsement of any type of water – I just figured it’s probably easily available). We also used Poland Spring water in the field today, to rinse our templates and knife between sub-plots. Why did we use that type of water instead of tap water or something else?

You might want to start on the Poland Spring website, and see if you can find any mention of mercury in any of their water quality reports. Why do bottled water companies and drinking water suppliers (like cities) test their water for chemicals?

Experimental designs

In environmental science, we often have to choose between two main study designs: one where we take lots of samples from lots of places all at once – but only once twice (a survey) and one where we take lots of samples from only a couple of sites, on many occasions or for a long period of time (often called trend analysis). Describe an instance (not one we've already talked about!) when you think each approach makes more sense. How might choosing one design over the other affect your results or interpretation?