These three instruments are used to study the overall purity of bodies of water, such as the Hatchie River:
The Oxygen Meter is square and gray with three shiny adjustable dials to the right of the gauge containing a thin red needle. It measures the amount of oxygen dissolved in liquids. Water in lakes and rivers should have at least 5 milligrams of dissolved oxygen per liter. Lower oxygen levels stress plants and animals, and higher levels can quickly kill many of the fish. A balance of plants and animals in the water keeps the oxygen levels healthy.
The pH Analytical Measurements instrument looks like a flat black box with a large white face on the top half. The face shows a scale with pH numbers from 0 to 14, and a hand similar to a clock marks how acidic or basic the water is. Connected to the box with a long wire is a yellow and green pen-like probe that goes in the water. If the pH is above 9, then the water is basic and can be harmful to a fish’s gills and skin. If the pH is below 5, then the water is acidic and may be taken over by moss or algae blooms that can kill a multitude of species living in the water.
The Stevens Type-A Water Level Recorder is positioned next to a body of water, with its hanging cylinder float placed on the water’s surface. As the water level changes, it moves the float up or down. Inside the silver box above, a clock controls the rolling of a paper chart, and a pen attached to the float records its movement on the chart. The float rests in a stilling well, which is a pipe with small openings into the water so that waves do not jostle it.
Instruments such as these are used at a stream gauge, which is a station on a stream where the oxygen, pH, and water level can be measured. There are currently two stream gauges on the Hatchie River measuring stream height and flow.