Last Friday, I brought my pH meter home and set it up on my dining room table. Frankly, I felt pretty eccentric doing that. I wanted to find out if there is a measurable daily cycle in pH within the marsh tide pool I’ve been studying. A main reason to expect a daily pH cycle is that carbon dioxide acts like an acid within seawater. During the day, plants and algae use sunlight for photosynthesis – they take up carbon dioxide and produce oxygen. At night, because there is no light, the plants and algae stop taking up carbon dioxide. It builds up in the environment (creating more acidity and decreasing the pH) because all of the animals, plants, and many microorganisms keep respiring – they use stored energy (food) and produce carbon dioxide. The pH in marsh pool could be interesting because the pools are usually cut off from the ocean, so they can have very big changes in water chemistry during the day.
I’ve already measured big daily cycles in temperature and oxygen. Animals living in the tide pool during the summer have to cope with very warm days and stifling nights. Think you have a hard time sleeping on a stuffy summer night? Imagine the oxygen concentration dropping to nearly nothing! I’ve measured a smaller salinity cycle, and episodic changes in water level with very high tides. But I still wanted to know about the pH. I don’t have a continuous sensor, so the only way to do it was by strolling out there and collecting samples. And since my house is pretty close to the marsh, it was easiest to set up the pH meter at home.