Lakes and ponds evolve through a natural aging process. Under natural conditions this process takes a very long time.

Cultural eutrophication, which is the acceleration of the aging process through human inputs, speeds up this aging process at an exponential rate. These human inputs include erosion, chemicals, fertilizers, waste runoff, leaky septic systems and more. The greater the level of the input the faster the lake or pond ages.

Chances are that the pond in your backyard is man-made. Many times these ponds are poorly designed, may have artificial water tables, and most are so shallow that within a few short years they pass from oligotrophic (new stage) to eutrophic (old stage).

Excessive runoff accelerates the aging process of a pond or lake exponentially. Special attention and management programs are necessary to overcome these effects of aging and keep these ponds and lakes productive and aesthetically pleasing.

Were you able to identify which categories your lakes are in? This is one of the first steps in creating a management program custom fit for your application.

We can divide the lake into regions based on location within the water body. Both the shape of the basin, morphometry , and the shoreline characteristics, morphology, have significant importance to the lake manager.

Inside these lake regions there are zones which have tremendous influence over water quality and our approach to management. These zones include the littoral, limnetic, euphotic, and benthic zones. Let’s take a closer look at these regions.

Morphometry and morphology have significant influence over mixing in the basin. Both vertical and horizontal circulation are important in creating and maintaining a balanced ecosystem.

Morphometry, or lake shape, has tremendous influence over horizontal mixing. Long narrow channels or canals often experience water quality management problems. Isolated peninsulas can create physical barriers to mixing and, water quality issues can more easily occur.

Morphology, or the shoreline characteristics of a lake, has significant impact over vertical mixing and plant populations.Different plants thrive at different depths.

For a more in-depth review of morphology we must begin by exploring specific shoreline characteristics.

First, the littoral zone is the region of the pond sloping from the shore out to the area of open water. It is the interface between the drainage basin and the open water, most generally the area where sunlight will penetrate to the bottom of the pond. The size of the littoral zone is dependent upon pond depth, clarity and wave action. Sunlight, wave action and the lake bottom have a great influence over this zone. Typically, this is the most challenging region of the pond to manage.

You will often see a ring of plants around the shoreline in the littoral zone. The variety and type of these plants are dependent upon depth. A variety of algae, including filamentous found in the littoral zone, will typically make up 90% of the species found in the lake. Algae in the littoral zone are often attached to macrophytes, which are emergent rooted aquatic plants such as rushes and reeds, and they thrive in this zone. Algae and macrophytes make excellent habitat for natural clean up tools like micro flora and zooplankton. Zooplankton are microscopic animals like protozoan, micro crustaceans, rotifers and larger invertebrates such as: aquatic worms, crayfish, insect larvae, and fish.

The second region of review is the limnetic zone, or open water zone. This is the area in the lake that starts at the intersection of the littoral zone and extends out into open areas of the pond. Shore and bottom lake areas will tend to have less influence in this lake region. Planktonic algae, water lilies, submerged pondweed, zooplankton, invertebrates and fish are commonly found in the open water zone. This lake region is typically easier to manage.

The third region for review is the upper, well illuminated layer of the water – or epilimnion. This is the area where photosynthesis by algae and other aquatic plants occurs.

The water column is the vertical column of water contained in the pond. This term is often used when discussing lake characteristics such as oxygen levels, temperature and nutrient content.

The fourth region for review is the euphotic zone or photozone area. This is the upper layer of the pond where sunlight can penetrate to promote the growth of green plants. We’ll review the importance of light to the aquatic ecosystem in just a short while.

Finally, the benthic zone is the area at the bottom of a pond or lake. The benthic zone is comprised of sediment and soil and usually has a high demand for dissolved oxygen.

Let’s put it all together…

The littoral zone is the shoreline area where nutrients will runoff into the water. The shallow nature of this zone and the fact that most nutrients will enter the basin through the littoral zone make it the most difficult area in the lake to manage. The limnetic or open water zone is deeper and easier to manage, while the euphotic zone is the region of the water column that is lit by the sun. Depending on turbidity, most of the lakes we encounter have euphotic zones that extend anywhere from 80% to 100% of the water column. And the benthic zone is the nutrient enriched, oxygen starved bottom layer of the lake.

A balanced pond management program will take all of these zones and regions into account and use each to help achieve ecological balance.

A pond in ecological balance is a healthy, dynamic ecosystem that is aging at a very slow rate where fish and other forms of aquatic wildlife are present, and there is an absence of foul odors and algae blooms. As nutrients enter the ecosystem they are either absorbed by the aquatic plants or metabolized by aerobic bacteria. There are safe levels of oxygen present in all regions of the lake with a minimum of 4 PPM or mg\l. Oxygen is added to the pond or lake from wave and wind action, the light side of the photosynthesis process, and rain. It’s a healthy, balanced ecosystem. Mother Nature has provided the necessary clean up mechanisms to keep the pond in balance.

However, this balance is a delicate one. Typically there is an influx of nutrients, as aerobic bacteria respire and consume oxygen they will metabolize nutrients. This process keeps the available nutrients at a healthy level and everything is fine until a hot, humid, cloudy day occurs when the planktonic algae doesn’t photosynthesize and create oxygen or the first long, hot night when oxygen demand soars.

In these scenarios there are no oxygen producers but there are many oxygen consumers, especially in stratified waters where all the demand for oxygen can’t be met. We experience an oxygen stress and in turn a fish kill where the lake then turns anoxic or anaerobic. The limiting factor is oxygen, while the fish kill isn’t the first indicator that there is a problem it’s usually the most dramatic and understandable one.