Leaf litter and detritus begin to accumulate locking up essential nutrients and interrupting chemical cycling. Plnkton begin to dissapear. Snails and clams absent 4.5-5.0 Mayfly and many other insects absent. Most fish eggs will not hatch. Dissolved Oxygen is the amount of oxygen that has dissolved into the water that is readily available for the aquatic life to breathe.
Oxygen dissolves directly into water from the air at the surface.
Fish affect D.O. when they respire, taking oxygen in and releasing carbon dioxide at their gills. Pollutants, including sewage, as well as decaying natural organic materials consume oxygen as they are broken down by bacteria and other microorganisms, lowering D.O. levels. When plant and algae growth increase, nutrients are consumed and nitrate levels drop. Nutrients get into water from human and animal water, decomposing organic matter and runoff of fertlizer from lawns and crops. This is a test of the amount of waste material in the pond.