Diatoms and dandelions

At the edge of the Horseshoe Slough parking lot, a middle-aged man stood staring intently at a dandelion gone to seed. After a long while, he lowered his hand and blew away the fluff. We stopped to chat for a minute or two, standing looking down at the chocolate water of the slough. He asked if we knew what made it that colour. I had a vague idea that it was algae, but no more information. He mentioned several other sloughs he had seen with similar colouring.

He started me wondering. So I've been Googling.

Brown water can be a result of several things; golden-brown algae, a conifer-dominated watershed, peat run-off, oxygen depletion, acidity. (I think there is some cross-over in that list.)Brown water in a ditch near the slough.

I Googled golden-brown algae. They grow in fresh and salt water; Horseshoe Slough would be brackish -- freshwater with an occasional influx of salt at high tide. They include thousands of microscopic species, and are an important foundation of the food chain. They include beautiful diatoms, which are said to be responsible for a large proportion of global CO2 fixation.

So: good stuff, it seems.

What may make this slough so unusually chocolaty is that it is a part of the Richmond bog system, which covered at one time about half of Lulu Island. The creek that feeds the slough runs down from the ancient bog, now mostly cranberry and blueberry fields, but still based on red-brown peat.
Browns and greens.
A trail follows the creek back into farm lands. Those are stinging nettles at the left, burdock at the right. Left to themselves, they would close off that path in short order. Behind them is a wild cherry tree, loaded with still-green cherries. Bird heaven!
And smaller weeds. I don't know what these pink flowers are. Some of the leaves look like creeping buttercup. Next: tiny blue flowers, hiding in the grass.