Ecology of a Pond

by sumansuman

This is an overview of the natural processes of an earthen pond, and the proper maintenance for a healthy pond.

Introduction

Pond ecology is best defined as the interaction of pond life with the environment that exists in the pond. A nutrient-rich, shallow pond with limited water flowing through it will become filled with algae and aquatic plants. Due to low oxygen levels, there may be little animal life present. In contrast, a freshly created, deep, spring-fed pond may also have little animal life due to low temperatures and a lack of food supply.

All ponds will age. A pond starts with water, little nutrients, and not a lot of animal life. Over time, the pond will increase in nutrients through a process called eutrophication. The additional nutrients will help with the growth of aquatic life. When these organisms die, their remains decay in the pond which releases the nutrients it took to grow them back into the pond water, thus keeping the lifecycle going.

An accumulation of material that resists decay will eventually fill up the pond and become a bog which resembles dry land. You want to slow down this process as much as possible. Here are some ways that you can achieve this.

Essential Nutrients

Growing aquatic life requires the four elements of carbon, oxygen, nitrogen, and phosphorous. Though it takes more than just these elements, there needs to be an abundance of them. To avoid the rapid aging of your pond (eutrophication), the levels of nitrogen and phosphorus need to be lower. Animal exposure to the water supply of your pond should also be restricted to limit the addition of nitrogen and phosphorus from animal waste.

Possible Buffers

Maintenance of vegetation in all areas where water needs to flow in order to reach the pond is essential. These buffers will slow the water down and filter it. When water is moving slowly, it causes a drop in sediment. Keeping sediment out of the pond will help prevent it from filling and becoming shallow. This directly contributes to keeping the pond from turning back into dry land. Deeper ponds are also cooler ponds, and the growth of organisms is slowed in lower temperatures. In conclusion, a buffer area helps maintain conditions that help slow the aging process of the pond.

Sedimentation Pools

Another method to keep sediment out of a pond is to provide a shallow pool at the inlet of the pond. Water flowing through this pool can drop sediment on its way to the pond. This pool should be small enough that it can easily be cleaned with a backhoe from the shore. A sedimentation pool is especially useful for sediment removal.

Limiting Fertilization

Whenever possible, decreasing the use of fertilizer on turf in the watershed area of a pond is beneficial. One of the reasons is because plant growth is efficient with the use of fertilizer elements. Applying fertilizers at appropriate rates will cause some elements, like nitrogen, to be unused and moved off-site. Reducing fertilizer rates will lower the amount of elements that move off-site.

Maintaining an Ecological Balance

Ideally a pond requires a complete and balanced food web. First, planktonic algae must be present in an amount that is enough for feeding zooplankton. The zooplankton will then be consumed by smaller fish and aquatic insects, and then they become food for larger fish. Then, the larger fish are prey for raccoons, bears, and fishermen.

The higher plant community is another part of ecological balance. Many plants are detrimental to the food web just described. From a pond owners perspective, a pond with a lot of vegetation lacks attractiveness, interferes with swimming, boating, and fishing. There are also issues for aquatic life. There are some aquatic plants that provide shade, hiding spots for small fish, habitat for aquatic animals and insects, and food source for some fish and animals. When the vegetation becomes overgrown, the angler’s hook gets tangled, and the bait is not as visible to fish. The excessive vegetation not only hides the bait, but it hides the prey making fishing unsuccessful.

Here are some other examples of excessive vegetation and the problems they can cause. Ponds that are completely covered with water lilies or lotus will block out sunlight, preventing the growth of any other vegetation underwater. There won’t even be sufficient light to grow planktonic algae. This will become an unproductive pond except for lilies. 

Another example is having too much duck week or water meal. When the entire pond surface is covered with these plants, like lilies and lotus, light cannot reach to sustain life beneath the surface. These plants deplete the water of oxygen because they become a barrier between the water and the atmosphere. As a result, the pond will become oxygen-deficient to a level that will cause fish to die.

However, you can eliminate too much vegetation or remove beneficial plants along with the targeted weeds. This is something to keep in mind when doing weed control in ponds. Some methods are for treating the pond in parts over time. For example, the use of mechanical methods or the use of grass carp to keep things “pruned up” as opposed to wiped out.

Maintaining Water Flow

When planning a new pond, water supply for the pond is key. Ponds that have a continuous supply of water function more efficiently than ponds with intermittent water supply. Ponds will experience significant water loss during the summer months. Ponds with an adequate inflow of water will stay full while others with less water inflow become shallow and unattractive when the muddy beaches are exposed. Continuous overflow into a pond produces better nutrient conditions because excess nutrients are taken away with the overflow water. Such ponds are likely to gather more nutrients at a rapid speed than an overflowing pond. Excess accumulation of nutrients leads to too much vegetation of all kinds, as noted above.

Aeration is Encouraged

Adequate oxygen levels in pond water are extremely important to the overall health of the pond. The value of the health of fish is easy to see. However, less obvious is the pond’s ability to get rid of waste. The waste that occurs in the ponds includes waste materials from animals that enters with stormwater runoff, as well as animals and plants that die in the water. 

Aerobic bacteria work about 20 times quicker than anaerobic bacteria in breaking down waste and putting it into solution. Once in a solution, it is able to grow new life, or it can be flushed out. 

The oxygenation of ponds happens in two ways. Plants and algae will perform photosynthesis during the day, and oxygen is added by the wind during the night. This is why the conditions that block light from the pond have to be monitored or disaster can occur like water meal covering the pond completely.

The oxygen produced by the water meal is released into the atmosphere, not the pond water. Areas of the pond that are too dark for photosynthesis to occur will become oxygen deficient unless the pond is being mixed from the surface to the bottom. To perform visibility check, you can place a Secchi disk into the water. The depth of disappearance will be recorded. Because of photosynthesis, surface water above the disappearance depth is oxygenated, while the water below that depth can only receive oxygen if mixed.

Another method of oxygenating pond water is by oxygen exchange with the atmosphere that takes place on the surface of the pond. The rougher the surface of the water is, the more quickly the exchange will happen. Also, the more oxygen-deficient the water is, the more rapid the exchange will occur. 

This process is crucial at night and for all ponds with an abundance of aquatic life. During the night, plants do cellular respiration instead of photosynthesis like animals. By dawn, the pond could become oxygen deficient if atmospheric aeration is hindered by a covered surface or lack of wind.

Pond Ecology in Winter

During the winter, water temperatures drop, and in some climates, ice will cover the pond’s surface. We will see the ways that these factors affect the animals living in the pond below.

Fish, frogs, and turtles are amphibians with adaptive features that can help when exposed to a dangerous environment. Their body temperature drops with the temperature of the water, decreasing their respiration rate and conserving energy usage. Frogs and turtles nestle in the middle and at the bottom of the pond for hibernation. They are able to do this by breathing through their skin.

Since ice blocks the entry of oxygen into the pond water through the surface, you may be curious how the low levels of oxygen that are required is supplied at this time. Enough light filters through the ice to cause photosynthesis for the aquatic plants. Ponds that are completely covered in snow can cause “winter kill,” the death of fish, turtles, and frogs. However, if you plow lanes stretching across the pond, clearing about half of the snow from the ice, this can prevent winter kill.

You should keep about 30% of the ice-free of extended snow cover. Be sure that removing the snow on the icy pond is safe. An alternative is using a diffuser type of aerator to add oxygen and keep a small area free of ice.

Summary of Pond Ecology

Ponds have a life cycle and limiting the inputs of nutrients into the pond is one of the best ways to extend and maintain the life of the pond. Catching sediment before it enters the pond, using less fertilizers around the watershed as much as possible, limiting access to water sources to animals, and preventing the addition of organic matter are all great preventative methods to use. A year-round supply of clean water causes nutrients to be flushed from the pond. Mechanical removal of overgrown vegetation will also help to remove significant nutrients from a pond. Finally, the use of aeration for supporting aquatic life and aiding in the decay of waste material is important. Keeping the pond surface free of plant cover and open to wind action will ultimately aid in better aeration.