About St. Mary's
Photo Album
St. Mary's Wilderness Liming Project

 Liming Information Sheet



What is liming?

Liming is a method used to treat acid in streams and lakes that have acid levels above normal levels due to acid rain or mine drainage. It is a general term that means a base is added to neutralize the acid.  In Virginia,  limestone (calcium carbonate) is used as the base because it is a natural material, is mined locally, is of high purity and dissolves slowly producing a long lasting treatment.


Where does the acid in St. Mary's Wilderness originate?

Acid rain is a general description of all forms of precipitation that have levels of acid above natural levels due to human activity. Rainfall is naturally acidic, but it is about 5 to 10 times more acidic in this area than natural levels due to the combustion of coal and other fossil fuels for power and motor vehicle exhaust.


What is the importance of geology?

To best understand why acidity is a problem in some streams, but not in others, the underlying bedrock geology and soils must be described.  The water chemistry of a stream is made of the chemicals that have been derived from the geology from which it originates.  In the Shenandoah Valley, large valley floor streams like the Shenandoah River flow over natural deposits of limestone which maintains a high level of base in the stream water.  Thus acid rain has little impact on the low lying streams.  The St. Mary's River and its Tributaries flow from low solubility bedrock formations (quartzite) typical of higher elevations that contains little natural base. The injection of acid in rainfall and other precipitation thus results in significant changes relative to the water chemistry prior to the industrial age.


What water chemistry changes occur due to acid?

The measure of acidity in stream water is called pH. The lower the pH, the higher the acidity.  Low pH causes aquatic life to suffer due to stress in mucous membranes and gills. Loss of calcium ion and other electrolytes occur which lead to disease and mortality. Aquatic insects and juvenile fish are most affected.  Aluminum is a naturally occurring element that is toxic to fish.  It is mobilized from minerals into the water when acidity levels increase. The decrease in pH is the result of the acid in rainwater and other precipitation removing the stream's acid neutralizing capacity or ANC. Measurement of ANC is an important means of establishing the vulnerability of a stream or lake to acid rain.


What does liming do?

When calcium carbonate dissolves it provides both calcium ions and carbonate ions.  The calcium ions are beneficial for aquatic life as mentioned above.  The carbonate ion reacts with acid to form bicarbonate.  This reaction neutralizes the acid which, in turn, improves the pH and causes aluminum to convert to an inert, nontoxic form.


What is the history of liming?

Liming has been used to fertilize lakes for many years.  In the 1980s, liming for mitigation of acid rain was studied extensively as part of the National Acid Deposition Mitigation program. In our neighboring state of West Virginia, expensive liming stations were constructed on some streams.  In Virginia we sought to develop a low cost approach. A study conducted from the late 1980s through the present time as a cooperative effort on the part of the US Forest Service, Virginia Department of Game and Inland Fisheries and James Madison University Chemistry Department involved a low cost method of introducing limestone sand directly into a stream (Little Stony Creek) at a single point and a single time. The intention was to replace ANC that had been lost due to acid rain with a minimum cost and a maximum amount of time before re-liming was necessary. Tests were done at JMU to determine the best particle size, best purity and amount of limestone needed to obtain multi-year treatment. The momentum of the stream flowing over the sand spread it down stream for 100-200 meters. Then as the stream flowed over it, the sand gradually dissolved providing a time release of the needed base. Extensive water chemistry monitoring and data collection has verified that the simple, low cost single application liming method can provide five years of treatment. Biological monitoring by VDGIF and the Forest Service has shown that fish and other aquatic organisms increased in numbers and diversity.  It is important to note that by this liming method we are seeking to replace lost ANC, not provide levels higher than would naturally have been available.  Thus the ecosystem should be in an ANC environment closer that which existed pre-industrial age.  In the ten years since the first liming was done, this liming method has been used to treat six other streams and two lakes in Virginia with significant success in water chemistry improvement and biological response.


What is unique about liming St. Mary's?

St. Mary's River is an important stream as it is the featured part of the Wilderness Area within which it lies.  As it is within a wilderness, no vehicles can be driven in to deliver the limestone. Thus a helicopter will be used to transport the material to the headwaters of the river including the feeder tributaries.  Dosages based on the existing water chemistry, the needed improvement and a desired treatment time of five years have been estimated and will be delivered to six locations.  This is not the first time helicopters have been used to transport limestone for acid mitigation in Virginia. Fridley Gap in Rockingham County was limed in 1993 and the headwater stream of Laurel Bed Lake in Russell County was treated in 1997.  But this is the first time a helicopter has been used to treat the main tributaries along with the main stem of the stream in a watershed treatment that will benefit most of the stream system.


How will the project be assessed?

Before and after the liming both water chemistry and biological data will have been collected.  More than twenty sites throughout the watershed will be monitored regularly for water chemistry by the JMU Chemistry Department. Aquatic insects will be surveyed by the JMU Biology Department.  The Virginia Department of Game and Inland Fisheries and US Forest Service will monitor six stations along the stream for trout and other species of fish. Physical measurements such as stream flows will be monitored by US Forest Service staff. Water chemistry parameters will include pH, ANC, base cations, acid anions and aluminum levels.  These parameters will be used to judge the effectiveness of the treatment and its longevity.


Is liming a cure for acid rain?

Liming only benefits the stream from the point of introduction downstream. It does not improve the forest or upstream of the liming site.  Since the limestone is slowly dissolving it will have to be replenished at some future time to continue the treatment. One justification for liming is that it can serve as an effective tool to protect an important aquatic ecosystem until such time as the overall problem of acid rain is solved.  Liming demonstrates to the public that there are real costs associated with the problem of acid rain adversely affecting aquatic ecosystems.


This summary was prepared by Dr. Dan Downey, JMU Chemistry Professor, to briefly describe liming in Virginia to non-scientists interested in the subject.


Top Of Page