Nutrients
Just like humans need food in order to grow and be healthy, plants need nutrients. In fact, most often in aquatic systems, the limiting factor that determines plant absence or abundance is the amount of available nutrients. In waterbodies unaffected by humans the most common limiting nutrients are phosphates and nitrates.
Problems with excess amounts of nutrients
A waterbody becomes unhealthy and overloaded with algae and other plants if too many nutrients accumulate. The first sign of excess nutrients is the presence of plant blooms. Plant blooms stress the aquatic community, because when the plants die, the dead plant material sinks to the bottom of the waterbody.
At the bottom of the waterbody there are numerous tiny organisms called decomposers (such as varieties of bacteria) that get nourishment by breaking down dead matter. Most decomposers consume oxygen. This means that as more dead plants accumulate at the bottom of a stream or lake, more decomposers accumulate to feed off of the dead plants. The addition of decomposers leads to increased oxygen consumption, often leaving little to no dissolved oxygen left for other animals such as the fish and mayflies. As a result, large animals are forced to swim to healthier, oxygenated water, while those that can't seek new water become stressed and may eventually suffocate.
Some pollution sources include:
- Fertilizer applied to agricultural fields, gardens and lawns
- Poorly maintained septic systems and sewage treatment plants
- Industrial effluent
- Pet, livestock and other animal wastes
- Detergents, particularly from car washing near storm drains
The three forms of nitrogen:
- Nitrate (NO3) is the most common form of nitrogen tested for, as nitrate-nitrogen.
- Nitrite (NO2) is less stable than nitrate, and usually present in lower amounts.
- Ammonia (NH3) is the least stable (or most reactive) form of nitrogen and, as a result, is difficult to accurately test.
Phosphates:
- Orthophosphate is the inorganic form of phosphate and most readily available to plants. It is considered the best indicator of immediate potential problems with excessive plant and algae growth.
- Phosphate is often the limiting nutrient for plant growth, because it is usually in short supply relative to nitrogen. As a result, very low levels of phosphorus can have huge adverse impacts on a waterbody.
