Site Observation and Testing
Dissolved Oxygen (DO) & Temperature Profiles – Dissolved oxygen is the most critical indicator of a lake’s health and water quality. Dissolved oxygen levels in natural waters are dependent on the physical, chemical and biochemical activities prevailing in the water body. Oxygen is added to aquatic ecosystems by aquatic plants and algae through the process of photosynthesis and also by diffusion at the water’s surface and atmosphere interface. Oxygen is depleted primarily by animal and plant respiration and decomposition.
Oxygen is required for fast oxidation of organic wastes including bottom muck. When the oxygen is used up in the bottom of the lake, anaerobic bacteria continue to break-down organic materials, creating toxic hydrogen sulfide gas in the process. For a healthy game-fish population, oxygen levels in the 6-10 mg/L range are necessary. Respiration stress in most fish occurs when oxygen levels are reduced to 4-5 mg/L. Temperature must also be considered when looking at oxygen levels in lakes since warmer water cannot hold as much oxygen as cooler water. A large difference between surface temperature and temperature at depth indicates that the lake is stratified, and is therefore in danger of having low oxygen levels below the surface.
Secchi Disk – This mechanical test to judge the depth of clarity of a body of water is accomplished by lowering a black and white disk into the water and recording the point at which it disappears. Higher values of Secchi disk transparency are found in very clear lakes.
Visual Algae Identification – Algae comes in different colors and some species produce toxins and/or odor compounds, so the first step in identifying it is to see it in its natural state. If the type or quantity is a problem, further tests will be conducted in the lab.
Aquatic Plant Identification – Different plants respond differently to herbicides, so identification of problem plants is absolutely necessary before treatment and many are easily identified in the field.
