History and effectiveness

Liming lakes and ponds is a tried and tested method for treating acidified surface waters, with studies is Sweden going back to 1984 (Nyberg). The aim of his studies was to study whether lime treatment was a possible method of protecting waters of special value for fisheries, nature conservation or recreational uses. In all waters where liming was tested it resulted in a sufficient and durable pH increase, the fish started to reproduce again, even if the populations were composed of very few and old individuals at the time of treatment.

Time treatment is not however a definite cure all for acidified waters, but may protect fish populations in lakes with long turnover times in areas with relatively low acid deposition. Areas of high runoff in streams, rivers and lakes with short turnover times are a lot more difficult to treat with lime and not recommended. In areas with a high acid load and acidified watersheds, liming of lakes and running waters will not prevent acid groundwater with elevated concentrations of toxic metals from entering surface waters.

Identifying liming needs can be accomplished by taking either a water or soil sample from the pond. Measuring the total alkalinity of water in the pond is the most effective and easiest way to determine if liming is necessary.

Liming enriches a lake by adding calcium, an important nutrient, and releasing phosphorus, another important nutrient, from the lake bottom muds. Production within the entire food chain (plankton-insects-fish) is stimulated by liming, and the increased abundance of natural food items supports sport fish growth and reproduction. Enhanced growth of rooted aquatic plants that serve as nursery areas for young sport fish can result from liming.

Adding limestone and fertilizer are conventional fisheries management practices for enhancing sport fish production in ponds, even in those waters that are not impacted by acid. They should not be applied simultaneously however because limestone may precipitate phosphorus and reduce its availability.

Liming is an effective tool in fish production and pond management. However, lime is casually used to describe two different types of materials, used for very different purposes.

Agricultural limestone refers to calcite (calcium carbonate) and dolomite (calcium magnesium carbonate). The calcium and magnesium components raise the hardness of water, essential to the health of many aquatic species. The carbonate component raises the alkalinity and the pH. Buffering daily fluctuations in pH increases microbial activity in the pond soil and also increases the availability of phosphorous to phytoplankton. Pond water with total alkalinity less than 20 ppm can benefit from liming.

Hydrated lime (calcium hydroxide) is an inexpensive and effective pond sterilizer, raising the pH quickly and dramatically above tolerable levels for most aquatic organisms. It should be used carefully, avoiding contact to the applicator, and never used in ponds containing desirable fish.