Yes, it does.
In any case, as the lake becomes more productive there’s more suspended particulate matter, particularly phytoplankton. There’s a shift toward back scattering of the longer wave lengths. You will get a more greenish kind of color and in a lake in which there’s heavy suspensions of clay, for example, the lake will look kind of a jade green because you’re getting a back scattering of light in that strong green range in the total light spectrum.
Back to my story. I was seeing this shift and it told me that the optical properties were changing. Generally speaking, limnologists assume if they see something like this that the lake is becoming more productive. Or that something is happening out there to increase the particulate matter in the water column. That particulate matter could be soil that is being washed off the caldera walls and continues to stay suspended in the water column, or it might be algae or phytoplankton. Phytoplankton are particles and they are suspended in the water column. If it’s an increase in the abundance of phytoplankton, then you ask the question well what’s causing this increase in the abundance? The first thing that comes to mind is nutrient enrichment. More nutrients are being introduced into the system either naturally or by anthoprogenic sources. This would cause the algae to become more productive and therefore more prolific and abundant. Nutrient enrichment will affect the optical properties of the lake because the increased concentration of suspended particulate affects visibility because more light is being scattered. The distance over which you can see in the water column diminishes because more light is being scattered, and less light is penetrating it. More nutrients change the spectral properties, and there’s this shift from the greater penetration of blues to a greater penetration of green. After that first summer I felt there might be a problem here and I thought the park should be aware of this. These could be precursors to a major change. Something could be happening to the lake. Maybe there’s [major] hydrothermal activity going on for all I know, so that nutrients are increasing. Mount St. Helens erupted in 1980 and, of course, in 1978 no one knew this would happen. Perhaps several volcanoes in the Cascade Range were heating up, increased heating in the bowels of Mt. Mazama could, propel warmer water and materials to the surface that had nutrient value; this could increase the production and proliferation of algae.
