Eco-Diary: Day 23

Here's what the creek looked like on September 22:

I noticed for the first time the difference in bottom composition in the creek. Along the edge of the north shore, there's a clear line of darker, richer soil next to lighter, sandier soil in the creek bed. The darker soil is presumably enriched by decomposing vegetation growing along the shoreline. Since the vegetation both anchors the soil and slows down the water as it passes next to the shore, the soil near shore stays put while the creek carries soil away once it extends beyond the protection of the vegetation. Or at least, that's my theory.

I'm curious about what causes this white foam (visible floating along the stick) to accumulate on the surface of water bodies from time to time: 

It wasn't there last time I visited. I've searched online but can't find anything that isn't specific to garden water features and backyard fish ponds. In the case of these, the foam is said to be caused by an excess of organic compounds in the water, notably phosphates. Since a backyard pond is an imitation of a natural ecosystem, things sh/could work in a somewhat similar fashion.

We know that phosphates occur naturally in living and decaying plant and animal remains, in soil, rocks, and sediments. I hypothesize that in a pond or stream, phosphate mainly comes from decomposing organic matter, mostly in the form of vegetation. A few days ago I noticed that the weeds on the bottom of the creek bed had started to die back. I haven't surveyed the entire creek, but based on the volume of weeds on the bottom just in my little bend in the creek, I suspect there is a pretty high volume of weeds throughout the creek — all of which I expect to be dying off at roughly the same rate. If that's the case, I think their death and decomposition would create conditions just right for surface foam.

I also took note of some of the trees around the creek. This one is growing on the north shore, just behind the cattails. It has quite large leaves:

And fairly smooth bark, like a beech tree:

But the leaves are double-toothed, and the veins are paired. The leaves of the beech are smooth and the veins are alternate. According to the key in my copy of Native Trees of Canada, it's either witch hazel or an alder. But the veins in witch hazel are alternate, and it doesn't match any of the alders, either. Of course, it could be an introduced species...

In searching for a link to R. C. Hosie's Native Trees of Canada, I came across another version: Leanne Shapton's Native Trees of Canada. Hers is an artist's rendering of the species described in Hosie's Canadian Forestry Service guidebook, which she came across in a used bookstore. It's not very useful for any scientific pursuits, but it's a great jumping off point for what could be a great visual art extension to any study of trees in a general science, ecology or botany unit.