What is Water Runoff?
Runoff is precipitation that did not get (infiltrated) absorbed into the soil, or did not evaporate, and therefore made its way from the ground surface into places that water collect. Runoff causes erosion, and also carry chemicals and substances on the ground surface along to the ponds, lakes and rivers where the water ends up. (eschooltoday.com)
Phosphorus and Nitrogen in Water Runoff
Ponds and lakes are categorized by their total phosphorus level and high phosphorus waters are considered polluted or “eutrophic”. Phosphorus is one of the key elements necessary for growth of plants and animals and in lake ecosystems it tends to be the growth limiting nutrient.
Biologically available phosphorus is found in lakes, waterways and wastewater in the form of phosphates. The discharge of reclaimed wastewater and watershed drainage will increase a lake’s phosphate level. Lawn and landscape fertilizer runoff are another major source of phosphate in lakes and their use should be avoided near the water.
Nitrogen is a product of the natural metabolism of plant and animal matter, and fertilizer runoff. Organic nitrogen can take many forms in water, including nitrate, nitrite, and ammonia. If ammonia is present in significant quantities, it can indicate that the water column does not have sufficient oxygen to oxidize ammonia to nitrite and nitrate. Reduced fertilizer applications near shorelines can sometimes help prevent increases in these. Both aeration and dredging can reduce this internal loading.
Water Runoff Can Reduce Oxygen Levels
Oxygen levels also can be reduced through over-fertilization of water plants by water runoff from farm fields containing phosphates and nitrates (the ingredients in fertilizers). Under these conditions, the numbers and size of water plants increase. Then, if the weather becomes cloudy for several days, respiring plants will use much of the available Dissolved Oxygen. When these plants die, they become food for bacteria, which in turn multiply and use large amounts of oxygen. And this depleting all the oxygen. (Lenntech.com)
How much Dissolved Oxygen an aquatic organism needs depends upon its species, its physical state, water temperature, pollutants present, and more. Consequently, it’s impossible to accurately predict minimum Dissolved Oxygen levels for specific fish and aquatic animals. For example, at 5 oC (41 oF), trout use about 50-60 milligrams (mg) of oxygen per hour; at 25 oC (77 oF), they may need five or six times that amount. Fish are cold-blooded animals. They use more oxygen at higher temperatures because their metabolic rates increase. (Lenntech.com)
Change the Water RunOff Effects
To slow or reverse the eutrophication process from water run off and maintain a lake or pond, beneficial microbes are critical. These beneficial microbes improve water quality by reducing the excess nutrients that flow into your pond.
1. Beneficial Microbes. AquaTron™ targets dissolved nutrients in the water column. These nutrients, if left unchecked, lead to poor water quality and increased speed of eutrophication. The beneficial microbes in AquaTron™ consume excess nutrients to improve water quality, increase water clarity, and slow or reverse pond degradation and eutrophication. Read More about Microbes.
2. Aeration. As anaerobic (devoid of oxygen) conditions begin to develop in the deeper water, naturally occurring aerobic microbes can no longer perform beneficial tasks, such as waste digestion or water purification. When compressed air is released at the bottom it will naturally begin to migrate towards the surface of the water. Read More about aeration.
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1. Lenntech.com http://www.lenntech.com/why_the_oxygen_dissolved_is_important.htm
2. ESchoolToday.com http://www.eschooltoday.com/water-cycle/what-is-runoff-in-water-cycle.html