When DO is low, only certain types of fish and aquatic insects will survive. Thus, surveys of aquatic insects and fish can often provide an index of long-term DO characteristics. The amount of oxygen that will be available in a water body is affected by water temperature. Fish follow these layers, because of DO and comfort. When it changes over a short period of time, something is 'happening'.
Alkalinity is the capacity of the lake water to neutralize acidity.
Again, this is usually a somewhat static parameter, dependent on chemistry of the surrounding soil and water body characteristics. Whatever frequency, a system should be established early on -before you begin. Sample frequency should be increased in the summer, when changes are more likely to occur. The U.S. Environmental Protection Agency also has information on voluntary monitoring.