We've all been there. You’re enjoying your pond and all is going along swimmingly. Suddenly, one morning you go outside and the pond has turned green or brown. Or maybe your fish are swimming funny. Something is off with the water quality! What’s happening?!?!
To truly understand and remedy what's going on with the ecosystem in your backyard pond, it's important to understand the basic tenets of pond ecology.
Let’s Start from the Beginning
The word “ecology” comes from the combination of two Greek words: oilcos, which means house, and logos, which means the study of. Translated literally, ecology means study of the home. In the big picture of life, it’s hard to comprehend all the interwoven intricacies of a global ecology, but if you scale it down a bit, it makes more sense.
Pond ecology studies everything that has an impact on, or is impacted by, a given pond. Looking at a backyard pond, let's see how many interactions we can find.
Studying Pond Ecology
The Substrate. We’ll start at the bottom and work our way up. The rocky bottom of a pond is alive and brimming with activity; covered in algae, microscopic invertebrates, and bacteria. This section of the pond is like the compost pile in a garden. When organic debris falls to the bottom of a pond, it’s broken down by the benthic (bottom) inhabitants.
These organic recyclers live off of uneaten fish food, decaying plant matter, and fish waste. If they were absent, the pond would “die” quickly, suffocated from toxic fish waste and organic build-up. Fortunately, nature has given us a way to solve this problem. Organisms have evolved and utilize practically every bit of available food. Fish, crustaceans, and aquatic insects will feed on these minute organisms, bacteria, and algae that live on the pond’s bottom.
The Water. The water in a pond is vital to all life within it. The unique properties of water allow nutrients to be kept in aqueous suspension. Plants and animals can absorb compounds directly from the water.
Pond water can be several colors: green, brown, white, and clear. Ironically enough, green water is the last thing a pond owner wants, but it’s the best thing for fish and other pond animals. It’s loaded with food; plantetonic algae are making the water green and they are a great food source for small insects and crustaceans, which in turn feed larger insects and fish. You know: the circle of life.
Brown water is caused by tannic acid released from decomposing leaves. In small amounts, this is not harmful, but it can become detrimental if left unchecked. White water is usually slightly whitish in color and is caused from high mineral contents. This condition is usually very short-lived in a closed system.
Gin-clear water is what everyone wants, but it’s last on the list in terms of productivity. It’s dead. If it’s clear, there’s not a lot of stuff (algae, diatoms, protozoans, etc.) in the water column. Slightly tinted water is ideal for backyard ponds. They’re healthier and more stable in terms of oxygen production and buffering of pH swings. They also offer a greater and more diverse food source for other inhabitants.
The Plants. Aquatic plants are typically considered pretty or nice to have in a pond. And algae are always considered the enemy. What we need to realize however, is that both are important in a healthy and functional pond.
Aquatic plants use the carbon dioxide and nutrients that are produced by the decomposers on the pond’s bottom. Plants also drink in sunlight to create plant tissue or stems, leaves, flowers, etc. Without plants, there will be a nutrient overload in the pond. In other words, nutrients will still be produced, but they have nowhere to go. That’s where algae come in. Algae start growing rapidly to keep the system in balance and use the excess nutrients. It’s like the first week in a garden.
Most pond owners don’t like algae. But it’s a cheap form of insurance that helps balance a pond and it keeps the nutrients from getting to toxic levels. In a healthy system, there will be strong aquatic plant growth as well as some algae. We just don’t want the algae to get out of control!
Aquatic plants and algae do more than just absorb excess nutrients. They produce oxygen for aquatic critters, provide shade from intense sunlight, provide food for insects and fish, and provide shelter for small pond creatures. Yes, water lilies and irises are beautiful and functional, but don’t overlook their importance in a pond.
The Animals. In ponds, animals usually steal the spotlight. Colorful fish, darting dragonflies, and friendly frogs grace the calm waters. Children spend endless summer days capturing tadpoles and watching them transform into amphibians. Can you believe it -- a biological oasis right in the middle of suburban America? Inside the pond, fish and frogs rule as kings, feasting on the generous helping of insects, algae and crustaceans.
Many pond owners feed their fish on a regular basis. But don’t forget that in a well-balanced pond, fish can feed themselves, making them fabulously easy pets to have! The nutrients that are not naturally produced in your pond, (i.e. fish food) need to be broken down into less harmful compounds. This is why biological filters are necessary in ornamental ponds. They break down toxic compounds produced from fish metabolism, over and above what’s being handled by the bacteria living on the pond’s bottom.
The Humans. Human intervention is necessary only because of human intervention! Clear as mud? In small ponds, life will balance itself. If x amount of food is available to support x amount of fish, then only x amount of fish will live there because the system can support no more. When humans step in and want 10 times more fish than a pond is designed to handle, intervention in the form of supplemental feeding and filtration systems is necessary. A backyard pond is a semi-closed ecosystem. It relies on us for its continued health.
In summary, all forms of life within a given ecosystem pond are interrelated and affected by one another. By killing off all the algae in a pond, you would be taking away an important link in the system, causing a shift in the food web and nutrient utilization. This will cause the entire ecosystem to restructure itself. We must learn to work within the boundaries nature has given us. Each link is important for the survival of the whole. That’s that whole food chain thing, again.
If we could only follow these simple “naturally balanced rules of life” in all our backyard ecosystems on a global scale, maybe life in Earth’s ecosystem would be much better. Understanding pond ecology and the "naturally balanced rules of life" will help you educate yourself so you can better maintain your pond.
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Barbi Holdeman, co-owner of The Pond Gnome, enjoys sharing their 20+ years of education & experience with you! She writes about Phoenix Ecosystem Pond Installation, Pond Maintenance, Wildlife around the Pond, Koi and Goldfish in the Pond, and the Pond Lifestyle. If you enjoy what she writes, please share it!