As winter weather gives way to longer days and warmer weather, a ponds shows signs of emerging from dormancy. Unfortunately, algae blooms are one of these signs. All ponds can get algae growth, so there is no need for alarm. But you should address algae blooms quickly, so you can avoid problems later. Some of the causes for algae growth are within your control.
Like other plants, algae photosynthesize, which means they need sunlight. The amount of sunlight each day grows longer after the winter solstice, which encourages algae growth. You can limit how much sunlight the pond gets by adding aquatic plants along the edges of the pond, or in the pond. An example is hardy water lily (Nymphaea "Comanche"), which grows in U.S. Department of Agriculture plant hardiness zones 4 through 10, and sports broad leaves that shade water. Wait until the days are warm enough to support plant life before adding aquatic plants. You may also have plants from the previous year that spent the winter in dormancy, but will emerge in spring.
Nutrients in ponds come from a variety of sources, including fish waste, detritus -- decaying organic matter, often from plants -- fish food that was never eaten and fertilizer carried into the pond through runoff. The result is an algae bloom as conditions become favorable. Rake out any dead and decaying organic matter from the bottom of the pond and skim the surface, removing algae.
Ponds need a certain amount of beneficial bacteria as another means of keeping the system in balance. These bacteria may die off or go dormant during the winter. The result is that there are fewer organisms to consume the abundance of nutrients accumulating in the pond. You can add more beneficial bacteria to the pond, which you can buy from pond supply stores, but you may need to wait until the pond’s temperature rises to a level that supports bacteria, somewhere around 40 degrees Fahrenheit. You can also turn on your pond’s biological filter system, which you may have turned off for the winter.
Dissolved oxygen levels are low in a stagnant pond. Algae thrive in low-oxygen environments, which is why ponds with no circulation are often coated in a film of bright green algae. When oxygen levels are low, and nutrient levels are high, the algae blankets the pond, preventing sunlight from penetrating. The tumbling action of circulating water adds dissolved oxygen to the water. Turn on the pump to create water movement in your pond to increases oxygen levels.
- Natural Environmental Systems, LLC: Algae Control 101 -- What Causes Algae and How Do You Control It?
- Live Aquaria: Pond Algae Control & Maintenance
- Pond Algae Solutions: Pond Algae in the Winter?
- The Ohio State University Extension: Planktonic Algae in Ponds
- University of Arkansas Cooperative Extension Program: Algal Blooms, Scums and Mats in Ponds
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