"Men and nature must work hand in hand. The throwing out of balance of the resources of nature throws out of balance also the lives of men."
Retention ponds are large bodies of water with a ring of rip rap or turf grass along the water's edge with the ubiquitous fountain in the middle spraying turbid water into the atmosphere.
We see them on a daily basis as they're a common feature throughout the country. They can be found in subdivisions, strip malls, office parks, industrial developments and even on rural farms.
These ponds are created for a very specific function of managing stormwater runoff which happens to be one of the biggest contributors of water pollution on the planet!
That's right, stormwater; it's a huge problem for several reasons, one of them being the unique structure of water. Water is also known as a Di-pole, meaning it has a strong positive charge on one side and negative charge on the other allowing it to attach to a wide variety of compounds. In fact water is known as the universal solvent because more compounds will dissolve in water than any other liquid!
This unique property is also responsible for keeping us alive as water is the vehicle for transporting a multitude of critical compounds, minerals and nutrients throughout our bodies. Water will also carry toxins away from our bodies in the form of urine and sweat. Without water, life as we know it would not exist.
During rain events water will fall to earth and in the process it will dissolve a wide variety of compounds that it comes into contact with. One of them being different forms of nitrogen; as rainwater falls through the atmosphere it comes into contact with nitrogen oxides created by the splitting of inert nitrogen (N2) found in the atmosphere created by the high energy of lightning. These new forms of nitrogen will dissolve in rainwater as it falls to earth. Here the rain will continue to dissolve a wide variety of nutrients, pollutants, herbicides, pesticides and heavy metals.
Retention ponds are a strategy to control these compounds along with the excess water generated from impervious surfaces. As water collects in the pond it will precipitate sediments and other compounds keeping them from going down stream.
The problem with this model is that all of this stuff continues to accumulate and during heavy rain events, the ponds overflow allowing all of the pollutants to continue going down stream causing problems in aquatic systems all the way to the ocean! So, how do we manage these water bodies?
Traditionally we pump them full of chemicals in an attempt to control the water quality but due to their very nature and design, they are constantly inundated with more and more nutrients and pollutants which feed algal blooms and disrupt the balance of the system. Chemical controls act as band aids to the real problem which is too many nutrients, also called eutrophication. The chemical additives will kill the algae but it just sinks to the bottom of the pond along with all of the other organic compounds such as leaves and lawn clippings.
One of the side effects of excess nutrients (eutrophication) is low dissolved oxygen. Because there's just too much stuff decomposing on the bottom, the bacteria will consume the available oxygen during decomposition until it's gone. This is why we see all of those fountains; water spraying into the air will increase the dissolved oxygen of the surface waters but it does nothing for the bottom of the pond where the oxygen is needed (breakdown organic compounds). With a lack of oxygen in the pond, fish become stressed and decomposition stops so organic compounds just continue to pile up on top of each other.
As the pond ages and sediments accumulate, the pond progressively gets shallower. A shallow pond allows sunlight to reach the sediment layer which causes excessive aquatic weed growth and algae blooms, which causes more chemical usage. Shallow ponds are typically warmer (warm water holds less oxygen) which speeds up the death of the pond and the entire ecosystem crashes.
According to the EPA the typical lifespan of a retention pond is approximately 20 years due to sedimentation buildup which will need to be removed and disposed of in order for the pond to continue to function.
I hope you see the madness here?!?!?
It's a brutal cycle but it's the only approved strategy out there and to be honest, it does work if you think about these ponds as stormwater management systems and not aquatic ecosystems.
If you want to actually increase water quality and the lifespan of the pond, it needs to be addressed differently. Think of it as an aquatic ecosystem.
Next week I will describe some basic strategies to help stop the process of eutrophication and increase overall water quality.