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UNDERSTANDING YOUR POND
Provided by Bioverse
Managing the water quality in your pond is a science that becomes more refined everyday. A thorough understanding of the ecosystem of the pond and the interactions that take place when you treat the water will assist you in successfully managing the pond.
Types of Ponds
Knowing the type of pond you have is important for understanding what type of issues you will be facing. Ponds are generally classified into one of three types: oligotrophic (new), mesotrophic (middle aged) or eutrophic (old).
Oligotrophic (new) ponds are either freshly built or have aged slowly due to the environmental conditions where they exist. They start out as clear ponds with low nutrient levels and few plants or living creatures. They generally have little algae present.
Mesotrophic (middle aged) ponds have an intermediate level of nutrients and plants. They experience moderate algae blooms on an intermittent basis.
Eutrophic (old) ponds generally have high nutrient levels, large amounts of sludge, turbid or cloudy water, and large algae and aquatic plant populations.
Ponds and lakes evolve through a natural aging process. Factors such as erosion and runoff from chemicals, fertilizers and waste can cause a pond to age more rapidly. Most ponds are man made and many times they are poorly designed and/or managed, so their aging process is sped up even more.
Pond Design
The goal of a properly designed pond is to minimize the nutrients entering the pond, so that the pond will achieve and maintain a balanced ecosystem.
 Size, Shape and Location
An ideal pond would have slightly raised edges called a "berm" to keep run off from entering. It would also have some flow through of clean water, from a well or a clean stream. The location should be away from leafy trees. Native plants and grasses should create a buffer zone on the shoreline around the pond at a width of 10 feet or more to filter nutrients before they enter the pond. This buffer zone will also keep the majority of waterfowl away, especially geese.
The size and shape of a pond has a large effect on water quality. The shape of the pond has an effect on how well the water circulates within that pond. Long, narrow channels tend to have more problems than wide-open bodies of water. Peninsulas, although aesthetically pleasing, create barriers to water mixing and movement. Shallower ponds and smaller ponds tend to have more problems. Deeper and larger ponds have a higher likelihood of maintaining a healthy and balanced ecosystem.
Pond Biology
Ponds may have up to four zones called the littoral, limnetic, euphotic and benthic zones. Each zone has an important role in pond water quality.
The littoral zone is the area of a pond nearest to shore. This region slopes from the shore to the center of the pond. Sunlight generally penetrates to the bottom of this zone, so that algae and aquatic plants can grow readily. Having aquatic plants in this zone helps the overall quality of the water by acting as the last line of defense to absorb runoff as it approaches the body of the pond, and is generally the most difficult area of the pond to manage.
The limnetic zone, or open water, is where the pond becomes deeper, and the bottom of the pond has less of an influence.
The euphotic zone is the upper layer of the pond water where sunlight can penetrate. The light provides energy to promote growth of green plants of all varieties.
The benthic zone is the bottom of the pond. It is comprised of sediment and soil, and usually has a high demand for oxygen.
Thermal stratification, or layers of temperature in water, is more likely in deeper ponds and lakes. As the sun shines, the pond surface warms and encourages more plant and algae growth. The cooler, denser water settles to the bottom. This becomes more significant as the summer progresses, and finally there is distinctive layering, and the layers do not mix. The line between the layers is called the thermo cline. The thermo cline acts as a physical barrier to prevent mixing between the top and bottom of the pond.
In the fall, as the water cools, the stratification is reversed, and the pond "turns over." The pond "turns over" again as the water warms in the spring.
Water Quality Parameters
The most important factors influencing water quality are: amount of sunlight/water temperature, nutrients in the water, pH of water, and oxygen levels.
Sunlight/water temperature
Sunlight is the primary energy source for a pond. It drives photosynthesis in plants and also drives water temperature. Shallow bodies of water, less than six feet deep, are generally more difficult to manage than deeper ponds because full light penetration and warmer water can cause more frequent and severe algae blooms.
Dissolved Oxygen (DO)
Adequate DO levels are important in maintaining superior water quality. Cold water holds more DO than warm water. In warm water zones the DO level is lowered, which has an adverse effect on most organisms. Additionally, with no turnover, DO is kept away from the bottom section of the pond. Low DO levels can lead to reduced microbial growth and minimal aerobic digestion of nutrients. DO is supplied to ponds by several sources such as photosynthesis and wind or wave action. Aquatic plants and algae produce oxygen-using photosynthesis whenever light is present. When there is no light, the plants and algae use oxygen. Wind and wave action allows oxygen to mix with surface waters, and allow oxygen to diffuse into the water. DO may also be increased mechanically through aeration. DO levels below three to four part per million will cause stress situations in the pond. The most immediate signs of low oxygen levels are fish kills and odor.
pH
The pH measurement is a ratio of acid to base. If a substance has one acid for each base, it is neutral and has a pH value of 7.0. Less that 7.0 is more acid and greater than 7.0 is more base (also known as alkaline). The pH level in a pond can vary widely due to the soil, algae, plants, source of water, or time of day the measurement is taken. For most ponds, the pH should normally be between 6.5 and 8.0 with the ideal range being 7.0 to 7.5. Unless the pH is below 6.0 or above 8.5, then it is usually best not to try to adjust it.
Alkalinity or buffering capacity
Alkalinity is the ability of the water to resist sudden pH changes. It is related to the amount of dissolved calcium, magnesium, lime and other compounds in the water. Alkalinity tends to be higher in hard water. If the alkalinity is low, it indicates that even a small amount of acid can cause a large change in pH. Alkalinity can be increased by evaporation, which concentrates the compounds or can be decreased through bacterial action, which produces acidic compounds that combine with and reduce the alkalinity components. In an established pond, the alkalinity measurement should be between 80 ppm and 180 ppm, with the ideal around 100 ppm.
Nutrients and runoff
Un-decomposed organic matter like leaves, grass clippings, fish and waterfowl waste, fertilizer and animal waste runoff, chemicals, and dead aquatic plants that end up in the water are a major source of nutrients that can cause an overload on the pond or lake promoting excessive plant and algae growth.
There is a direct correlation between amount of available nutrients and the population of algae and aquatic plants. It is important to understand the source of these nutrients, and the most important nutrients are phosphorus and nitrogen. Phosphorus has been identified as the single biggest contributor to aquatic plant growth. A single gram of phosphorus will produce one hundred grams of algae.
The three most common sources of nutrients are dead vegetation/silt, runoff from the area surrounding the pond, and components of the incoming water.
As vegetative life ends, it sinks to the pond bottom, adding to the nutrient level for future aquatic growth. This is called nutrient cycling. The sediment or sludge at the bottom of the pond can accumulate at a rate of one to five inches per year or more. This rate is higher in warm, nutrient rich waters. From a practical perspective, in an irrigation pond of roughly one acre of surface area, this type of sedimentation reduces water storage capacity by 80,000 gallons per year. Naturally occurring bacteria are present in all ponds, but generally are not present in large enough numbers to combat the sedimentation and extra nutrients available.
The second source of nutrients is from runoff from the area surrounding a pond. Reports state that up to 4% of the fertilizer applied to the area adjacent to a pond may runoff into the pond. This nutrient rich runoff is called nutrient loading. Leaves, grass clippings, and animal waste further add to the nutrient loading.
Nutrients, like all things in a pond, are continuously recycled. Nitrogen, phosphorus, sulfur and carbon undergo complex cycles as they are converted from one form to another to satisfy different parts of the food chain.
Finally, nutrients can be added to ponds through incoming water. The incoming water may be effluent water from a treatment plant, or nutrient rich water from other sources. Incoming water, in addition to the composition of the lake bottom, contribute to pH of the pond water. The pH describes how acidic, or how basic the water is. Rainwater is in the 6.5-7.5-pH range. Vinegar has a pH of 3 or less, soap has a pH of 10 or higher. If the pH is below 6 or above 8, the water will not allow naturally occurring bacteria and other microscopic creatures to function at their peak efficiency. This allows algae to take over.
In summary, balance is critical in the pond. A healthy pond contains balanced amounts of oxygen, nutrients, and water clarity.
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