We don’t hear as much about acid rain in the news any more. Certainly not like we used in to the 70’s or 80’s. Back then, new research was emerging that indicated that rainwater was becoming more acidic due to emissions of sulphur dioxide and nitrogen oxide. Most of these emissions come from the burning of fossil fuels released by automobiles, or power plants that use coal or oil to generate electricity. Nature can also produce some of these gases, such as when volcanos release various gases into the air.
The gases that are produced from these processes end up combining with water vapor in the atmosphere and form nitric and sulphuric acids. So the term “acid rain” is actually quite accurate in it’s description.
But a question came up regarding acid rain. Since we don’t hear so much about it anymore, is it still happening? Is it a problem? And specifically for a pond owner (which is who this article is mainly for), can it affect my pond in any way?
Let’s cover first things first here.
Although there’s no question that in most places around the U.S. air quality standards have improved since the 1980’s. How much is probably debatable but with some technological improvements, there is evidence of emissions from the sources mentioned above being a bit more limited. Despite this, some emissions are still taking place, and with other countries around the world becoming more modernized, it’s a good bet that acid rain is still a common issue, even though you might not hear about it in the news as much.
Here’s a recent article from Science Now that discusses research in the recovery or improvement in soils once affected by acid rain and it does show signs of improvement. However it doesn’t really take a scientist to realize that we still use coal to provide power, we still drive a lot of cars, albeit with improvements, volcanos still spew gases, and we’re still affecting the atmosphere with these kind of activities.
What all this comes down to is the fact that acid rain still does exist. To some extent it continues to affect the soil and plant life, but it can also affect water and more specifically, pond water.
How Acid Rain Affects A Pond
We’ve talked in the past about the chemistry of pond water. One of the main things we like to keep an eye on is the pH of the pond in terms of where it reads, but also how stable it might be. By definition, pH describes the acidity or alkalinity of a solution, or of water.
pH is measured on a scale of 0 to 14, with 7 considered neutral, below 7 being acidic, and greater than 7 defined as basic. A lower number represents a greater number of hydrogen ions, and each pH unit represents a 10-fold change in the hydrogen ion concentration and amount of acidity. For instance, a pH of 6 has ten times more free hydrogen ions than a pH of 7, and one hundred times more free hydrogen ions than a pH of 8.
And there is fairly conclusive evidence that acid rain can affect pond water.
In fact the Environmental Protection Agency has stated that, “the ecological effects of acid rain are most clearly seen in the aquatic, or water, environments, such as streams, lakes, and marshes.”
The EPA has created a webpage that details the effects of acid rain on aquatic life, and I’d encourage you to read this in it’s entirety when you have some time. To summarize things a bit, when acid rain falls, it will saturate the soil and the acid causes aluminum to leach from the soil and the runoff goes into streams, ponds, etc. Along with this, the acid in rainwater will cause the pH of the pond water to shift downward and this combination of low pH, and increased aluminum levels can create an environment that’s directly toxic to fish.
More moderate changes in these readings may simply create stressful conditions for the fish which may not kill them outright, but it can retard growth rates and reproduction. Some species tolerate changes better than others. For instance snails can be affected with a pH below 6.0. Bass are prone to issues at 5.5 or less, and trout at readings of 5.0 and lower. Most fish eggs won’t hatch in readings of 5.0 as well.
For small pond owners who tend to have a more controlled ecosystem to work with, acid rain’s main influence is with the pH of the water. Since there is usually some turnover of the water in small ponds, where fresh water may be added fairly often, the source water that’s used probably has a greater influence on pH, but rain water certainly can have an affect as well.
Probably the most troublesome thing for pond owners and their fish, isn’t simply a low pH. As the numbers pH numbers indicate above, fish can handle a pretty wide range. Usually they’ll do OK with anything between 6.0 and 9.0 or even a bit higher. So it’s not so much the pH that’s the problem, but trouble comes when the pH shifts rapidly. Throughout the day, pH may never be constant, it can always shift, but wide swings create more problems for fish, than more moderate ones.
So What Can You Do To Protect Your Fish?
Since our primary consideration with pH and fish, is to limit any big swings in the numbers during a short period of time, the goal here is simply one of stability. Despite the influence of weather and other things, we want the pH of the water to remain as stable as possible and to do that, we need to focus on it’s buffering capacity.
I put together an article and video on buffering pond water a few years ago and it’s still a good resource for some basic ways you can bring stability to a pond. For small ponds this can include the use of baking soda or sodium bicarbonate. For larger farm ponds you can consider adding lime to help buffer the pH. Searching online will usually provide some helpful advice and dosages for liming, but here’s one good example from the Sound Carolina Department of Natural Resources.
When all is said and done, acid rain probably isn’t too much of an issue for most pond owners, but some may be affected by it. I wouldn’t lose sleep over this every time it rains. Like we always say here in Iowa, we can’t do much about the weather, other than to live with it and complain about it. And it’s true, we can’t control the weather, but with a few simple steps, you can protect your pond and your fish a bit more just in case things get a little crazy in your part of the world.
Do you think your pond or fish have ever been affected by acid rain? Share your experience in the comments below…