Strategies for Ecological Pond Management

By Ronald Pifer

MA Environmental Biology, Univ. of Colorado

BS Engineering, Duke University

Society of Sigma Xi, Scientific Honor Society

 Ponds are complex environments that contain a dynamic combination of living and non-living components. The living components may include animals, such as fish, turtles, and frogs, as well as occasional visitors, such as waterfowl, pets, and livestock. The pond’s plants may include various rooted aquatics, floating aquatics, suspended aquatics, and slimy aquatics that lay on the surface and dangle to the bottom. Additional life forces include natural pond bacteria, fungi, and other decomposers.

The non-living portions of the pond include the pond’s submerged surfaces, as well as any rocks, minerals, and nutrients. Natural earthen bottoms can have most of these ingredients, while ponds with plastic liners usually lack soil and rooted aquatics. Nonetheless, both aquatic environments contain essential raw materials that provide substance to the pond’s ecosystem, along with natural gases, such as oxygen, carbon dioxide, nitrogen, hydrogen sulfide, and methane gas.

Naturally, all of these factors must be in proper balance, in order for your pond to be healthy.  This balance can be established with your help and by following various trusted and proven guidelines. These guidelines will be discussed next, under the headings of pond bottoms, aquatic plants, and aquatic animals.

Pond Bottoms 

 All submerged surfaces are covered by a slimy substance that contains a microscopic community of microorganisms, such as bacteria and fungi, plus various nutrients, minerals, and organic matter. This film is called a bio-film and it is the locality where over 99% of the pond’s bacteria are found, according to the Bio-Film Engineering Center at Montana State University in Bozeman, Montana.

The bio-film of an earthen pond covers the sludge layers on the pond’s bottom, as well as all the other submerged surfaces. The sludge layer may be several feet thick, depending on the age and past biological activity of the pond. This layer usually contains decomposing organic and inorganic material, and it is quite often anaerobic, or low in oxygen. This condition provides an environment for pathogens, indicated by the presence of the bacteria, E. Coli, and it often provides the source of a “rotten egg” smell around the pond. This later condition is due to decomposing bacteria, working without oxygen and producing hydrogen sulfide gas, instead of carbon dioxide or nitrogen gas.

The bottom of a lined pond should not have the sludge buildup of an earthen pond, and it is easier to manage. It does have a bio-film, however, and it is actively processing the nutrients that algae need for their subsistence. Both pond bottoms respond well to the presence of introduced bacteria and enzymes, which eat the organic film and remove or bind up the essential nutrients that algae need to survive!

Aquatic Plants

The plants in an aquatic environment can be placed in three main categories: (1) the suspended, single-celled algae, called phytoplankton; (2) the floating, multi-celled algae; and (3) the rooted aquatics. The phytoplankton are the ones that provide a green, or blue-green color to the water. They are most sensitive to the nutrients conditions in the water column, so they are the ones who will disappear most rapidly if nutrients are removed by bacteria and enzymes.

Common floating aquatics include the stringy algae that form mats on the surface, as well as duck weed or water bead, which are small floating plants. When these plants are confronted with the removal of pond nutrients by bacteria and enzymes, the stringy algae have been found to be the most sensitive, followed by duckweed and water bead.

Rooted aquatics include many different varieties of plants, and they have root systems that extend into the ground, underneath the pond. They are less sensitive to the nutrient conditions in the pond, since they derive much of their nutrient requirements from the soil. Therefore, they are better managed by mechanical removal or the presence of grass carp, which gradually eat the rooted algae, as they graze and grow bigger. Mechanical removal is only practical in smaller ponds and water gardens and around the edges of larger ponds. Grass carp are not available in some states, so you would have to check with your local Fish and Game representative for their legality and availability in your state.

Aquatic Animals

Ponds contain all kinds of aquatic animals, including those that have been introduced, as well as those that migrate. Some animals are small and provide an important lower link in the food chain, while others, such as fish, frogs, and turtles, are larger and feed at the top of the food chain. Additional inhabitants can include various water fowl, such as herons, ducks, and geese.

All of these animals contribute waste products to the pond environment, which must be decomposed by the native and introduced bacteria. These waste products are mostly organic in nature and they contain the nutrients that are essential to the production of algae, particularly the phytoplankton, suspended, and floating algae. Control of these algae can be accomplished directly with poisons, which have the potential to accumulate in the environment. On the other hand, alternative measures can be taken, which use introduced bacteria and enzymes to remove the nutrients that algae depend on to survive. This approach is an indirect approach, because the bacteria are sludge eaters and processors, and they do not directly poison the algae.

The most serious animal contributors to a pond environment often include geese and ducks, which often make algae problems much worse by their presence. High concentrations of fish can also contribute to an organic and algae nutrient buildup, due to their normal waste discharge and the decomposition of uneaten fish food. Furthermore, livestock can also contribute to the organic load in a pond and can cause all kinds of problems for pond management.

However, in all cases, a combination of ecological and natural approaches can put your pond environment into proper balance. First of all, the nutrient buildup needs to be reduced, which is most directly accomplished by the introduction of beneficial bacteria and enzymes. Secondly, grass carp can be an added asset in those states where their use is allowed. Also, the addition of an aeration system is most helpful, since the presence of high oxygen levels helps both the introduced and the native bacteria to work more effectively. In short, a clean and healthy pond is a happy pond, and a happy pond is good for all creatures, large and small!