Waves in the Creek

Waves in the creek.
Waves in the creek.

We talked about waves today down at the creek. The water was fairly calm so we could make some nice surface waves using floating leaves to show the up-down/side-to-side motion as the waves passed. I gave them 10 minutes to “play”, and more than one team tried to make a tsunami.

Creating a large wave.
Creating a large wave.

Since it’s allergy season, one student who could not go outside, read the chapter on the characteristics of waves and prepared a short–5 minutes–presentation for the rest of the class when we came back in.

Annotated image highlighting the crests of the waves and the wavelength.
Annotated image highlighting the crests of the waves and the wavelength.

Water Levels in the Creek

A relict puddle at the end of the summer (mid-September).
A relict puddle at the end of the summer (mid-September).

It has been remarkable to see the drying of the creek over the relatively dry summer.

Spring.

Flooding creek after spring's showers (mid-April).
Turbid, fast-flowing creek after spring’s showers (mid-April).

Mid-Summer

Mid-summer.
A clear sedate creek in mid-July.

End of the summer.

The dry creek bed in mid-September.
The dry creek bed in mid-September.

Crayfish: Charismatic Mesofauna

This year, the creek is teeming with crayfish, especially compared to last year during the drought when the creek dried up and the crustaceans were hard to find. I had five students out collecting organisms on Wednesday, and they came back with ten crayfish ranging in size from a couple centimeters long, to one that was about 12 centimeters from claws to tail.

Crayfish in a jar.
Crayfish in a jar. Seen through stereoscope. Magnification unknown.

I was just looking at one of the pictures I took and realized that I did not know what species it belonged to. I’ll be having students do reports on individual species for biology next year, and I’d be very surprised if someone did not choose crayfish. They’re so many of them and, as my students from Wednesday will attest, they’re just so charismatic. While I’ve not looked into it much myself, the Crayfish & Lobster Taxonomy Browser seems a decent place to start researching.

Red-eared Slider

Rescued red-eared slider.

This little guy was rescued just down the road by one of our bicyclists. His under-shell, which is called the plastron, is beautifully decorated.

It’s in the fish tank with the tadpoles at the moment. Red-eared sliders grow to 12-25cm long, and they’re named after the red splotch that’s located just behind their eye.

It seems happy enough in the tank, but we’ll release him to the creek at the end of the semester in a couple weeks.

They’re native to Missouri, but according to the Missouri Department of Conservation’s nice little reference book, Show Me Herps, these have been the targets of illegal collection, and international trade. Ones released in Europe have become invasive species there.

The red “ears” aren’t really ears, just a patch of red behind the eye.

Albedo and Absorption

Ice melts around an embedded leaf, taking the pattern of the leaf.

Darker colored objects absorb more light than lighter colored objects. Darker objects reflect less light; they have a lower albedo. So a deep brown leaf embedded in the ice will absorb more heat than the clear ice around it, warming up the leaf and melting the ice in contact with it. The result, is melting ice with shape and pattern of the leaf. It’s rather neat.