I’ve been asked for information about removing iron from your pond water being used for irrigation. We have dealt with this problem many times during our 31 years in business. Rust from oxidized iron in irrigation water can stain driveways, sidewalks, fences and even ornamental plants. Lakes and ponds can be very good irrigation water sources. But, just like all other water supply sources, problems can occur that need solutions.
It is important to know that high iron is not the only potential cause for yellow, brown, orange or red stains from irrigation water. Planktonic algae and tannin pigments from decaying leaves and pine straw are other potential sources for the discoloration. I will assume that your problem is indeed high iron content.
Iron can occur in several different forms in your pond. The depth, chemistry and dissolved oxygen content of the water determine the form of your iron. There are also certain bacteria in water that may affect the form and availability of iron in your water. Acidic water (pH less than 7) favors the dissolved (ferrous) form. The precipitate (ferric) form is rust because the iron is oxidized by being exposed to oxygen. Rust will usually settle to the pond bottom but may change back to the soluble form if the bottom water is oxygen deficient. Agricultural lime can be added, usually 2 – 3 tons per acre of pond surface, if acidic water is an issue.
Irrigation problems with water high in iron are common and several solutions are relatively simple and inexpensive. In my experience simply aerating and circulating the water along with properly positioning the irrigation pump intake solves the vast majority of the problems. If that is not sufficient, the solution to your problem will require determining the form of iron causing your problems. Analysis of a properly collected water sample can help determine the most cost effective solution, usually some sort of filtration.
One of the easiest solutions is having the irrigation pump intake at the proper depth in the water. The pump intake should be between 18 and 30 inches from the pond water surface. Intakes too close to the pond bottom can suck up iron rich sediment that has settled to the bottom. Intakes too close to the surface can suck up iron fixing bacteria and more of the oxidized form of iron that has not settled to the bottom. The depth of the pump intake can be set by suspending the intake below a float or building a rack or stand for the intake. We usually suspend the intake below a float. Then, it is easy to lift the float and clean the intake if it becomes clogged.
Most of the iron in problem ponds I have seen can be precipitated and caused to sink to the bottom of the pond if the pond is aerated and circulated. Diffused air systems are usually very efficient and cost-effective for aerating and circulating ponds. Diffused air systems use a small compressor, located on the pond shoreline, to push air through weighted tubing to diffusers installed on the pond bottom. The diffusers produce millions of small bubbles with the compressed air. The bubbles each enlarge as they rise towards the pond water surface (due to declining pressure) and the column of bubbles spreads out significantly as it rises through the water column. The resulting column of bubbles transfer some oxygen to the surrounding water and, more importantly, pulls a very large volume of water from the pond bottom to the surface. At the surface the water is exposed to air as it spreads out in all directions from the “boil” of bubbles.
The iron in the water is oxidized by the oxygen in the bubbles and atmospheric air at the surface. The water is circulated throughout the water column. Diffusers in deeper water are more efficient because they circulate greater volumes of water. Much of the oxidized iron will form a precipitate (particles of rust) and settle to the bottom of the pond. If the pump intake is suspended off the bottom of the pond the “rust” will not be pumped into the irrigation system. The size of the compressor needed will be determined by the number of diffusers needed. The number of diffusers will be determined by the depth and the shape of the pond. We are experts at designing these systems and most customers are surprised at the low cost for purchasing and operating the systems.
Foster Lake & Pond Management provides the full range of lake, pond and stormwater BMP services and products. These include: construction, repairs, maintenance, certified inspections, fish stocking, fisheries management, lake mapping, vegetation management, docks, fountains and aeration.
We have provided aquatic and stormwater solutions to our North Carolina customers for 30 years. Call us at: 919-772-8548 or visit: www.FosterLake.com.