That time of year is approaching. Hot days are waning, giving way to pleasant afternoons and cool nights. The leaves are taking on color here and there. School buses are rattling down residential roads. And the odor of Grandma’s attic comes spilling out of the faucet.
‘Tis the season for lake churn, when water smells musty, customers complain and water operators must deal with both issues on top of everything else.
This issue of eBulletin will talk about lake churn, or lake turnover, what it is, what can be done (if anything) to counteract it and how to deal with the customers who worry or complain about it.
The Twist
Let’s start with the basics. What exactly is lake churn or turnover, and why does it happen?
It’s a fairly simple concept. Most lakes and reservoirs are deep enough that water settles into layers based on temperature. In the summer, the coldest water settles to the bottom while surface water stays warm. During the fall, dropping air temperatures cool the surface water, making it more dense and causing it to sink into the middle and lower layers of the lake or reservoir. The denser water displaces the other layers, forcing them to the surface. As the water circulates, the higher-oxygen upper layer helps bring organic and nutrient material to the middle and lower layers as well as the bottom of the lake. A basic illustration can be seen in the graphic above from the U.S. Forest Service.
Water systems vary on which layer they use to draw down their water, but lake churn forces extra organics and nutrients into all these layers. It’s those organics, including bacteria and other elements, that give the water that earthy, musty smell and taste.
The opposite holds true for the winter and spring. Cold air temperatures cool the water surface. Ice is actually less dense than cold water, so it floats and keeps the coldest water at the surface. Warm spring temperatures heat the water to the same temperature as the middle layers, and spring winds help send the water circulating. This is spring turnover.
Lake churn occurs more with large, deep reservoirs. Smaller, shallow reservoirs tend to stay more mixed thanks to surface winds that keep the water in motion. In milder climates, such as in the south, fall turnover often has more of an impact than spring, because the water doesn’t get as cold in the winter.
Turnover can be as short as a few hours or as long as several days. The effects, however, can linger as organics in the water mix and resettle.
For an idea on how lake churn affects large bodies of water, check out the EPA’s explanation in its new Great Lakes guide and the Illinois EPA’s PDF document titled “Lake Stratification and Mixing.” All three links are below.
Additional Resources
EPA: The Great Lakes – An Environmental Atlas and Resource Book
http://www.epa.gov/glnpo/atlas/glat-ch2.html#Lake%20Processes [1]
Illinois EPA: Lake Stratification and Mixing
http://www.epa.state.il.us/water/conservation-2000/lake-notes/lake-stratification-and-mixing/ [2]
That Smell
The most obvious sign of lake turnover or churn is the smell. Most describe it as musty, earthy or moldy. Sometimes, even the taste of the water can be affected, giving it a stale or earthy flavor.
This is caused by added bacteria and nutrients dissolved in the water as algae is broken down and circulated during lake turnover. While such bacteria is often present, it usually sticks around the upper and middle layers of water, above most draw-down levels.
The smell and taste change is most often caused by the breakdown of cyanobacteria, or blue-green algae. The biggest culprit of that musty smell is 2-methylisoborneol, or MIB. The chemical can be at least partially removed with powdered, activated carbon, which many systems use to counteract the odor and taste. However, the carbon or other chemicals may not get all of the MIB, especially during heavy churns caused by rapid or significant temperature changes. In that case, water operators and customers may just have to live with the funky odor and flavor for a few days.
Diane Boudreau explores the reasons behind the smell and taste in her article “Stinky Water,” which appeared in the Arizona State University magazine Chain Reaction.
The article discusses the research project by ASU scientists to discover why Phoenix water sometimes took on a musty smell and what could be done to curb or prevent it.
Besides MIBs, she also mentions another chemical that leads to that unusual smell. Geosmin, also produced by algae breakdown, can produce a smell and taste of dirt in drinking water.
Spring and fall turnover may be the most common times to encounter that musty smell, but hot summer days can lead to it as well.
Excessive heat and stagnant or slower flowing water can promote algae growth, which leads to that earthy stink. If this is a common problem during the summer, it may be a good idea to add aerators or agitators to your water source to keep the water from being stagnant too long. It may also require adding chemicals to help prevent algae growth.
Additional Resources
“Stinky Water,” Chain Reaction magazine
http://chainreaction.asu.edu/pdfs/issue4/chreact4_p22_25.pdf [3]
Bridge Over Troubled Waters
The biggest challenge during these events isn’t dealing with lake turnover – it’s dealing with the customers.
Customer complaints are inevitable during lake churn season. Longtime customers probably won’t think anything of it, but the newer ones may be more quick to phone. Some will be nice, calling just to inform you of the smell. Others may be a bit testy or demanding, the standard “for what I pay, my water smells like this?” complaint. Many may be worried and will ask the most common question during lake turnover events. “Is it safe?
So how do you reassure the public that the water that smells like it’s from 1904 really is OK to drink?
The best way is to get the word out about lake turnover. The press is an excellent way to do this. Press releases to local newspapers and television and radio stations should briefly describe what lake turnover is. You should also state how often testing is conducted to make sure drinking water stays in state and federal compliance. Explain what is being done to counteract the turnover effects, and if possible, give an estimate of how long these effects are expected to last.
It also wouldn’t hurt to put that same press release on your water system or city’s Web site, if one is available. Provide contact information as well. You may get a lot of phone calls or e-mails, but it assures the public that someone is there when they need their fears laid to rest.
Another option is to put a brief explanation in with the water bills prior to the usual spring and fall turnover times, often August or September for the fall turnover and March or April for the spring turnover.
There are a few examples of press releases and Web site cautions available online. One example of an informative brief can be found at the Raleigh, N.C., News & Observer’s Web site. The city of St. George City, Utah, provides a good announcement on its Web site. In its case, summer algae growth combined with a lack of powdered carbon to create a musty water supply. The city explained the cause, the symptom and the cures in detail. These could serve as models for crafting your own information based on your reservoir’s annual behavior.
The main thing is to reassure the public that while the water may smell or taste "funny," it is not a health risk and meets or exceeds all state and federal requirements.
Additional Resources
“Algae upsets taste, odor of water”
http://www.newsobserver.com/news/story/674798.html [4]
“Water is safe to drink despite musty taste and odor”
http://www.santaclaracityutah.com/pdffiles/odor_in_water_06.pdf [5]
Don’t Pass Me By
It may be easy during lake churn events to chalk customer complaints up to turnover, but don’t be too quick to dismiss them. Their complaints could be warning signs of other issues.
It’s a good idea to keep track of how long lake churn events occur with your water source. If an event seems prolonged, there could be other issues, such as source water contamination that’s causing explosive algae growth. If a churn event lasts more than a few days, it wouldn’t hurt to inspect the water source to determine if any leaks or contamination have occurred.
Also, listen to the descriptions in the complaints. “Musty” or “earthy” can be attributed to churn, but “rotten eggs” or “sulfur smell” may mean a break in the system, an outside or unnatural contamination or an imbalance of nutrients or chemicals.
Most complaints, however, probably will center around the lake turnover. While it seems to cause a lot of problems, turnover is actually a good thing. It keeps the lake and its nutrient-rich inhabitants alive, and the circulation keeps algae blooms from getting out of control. Too much algae can cause major problems for water systems, because all those broken-down chemicals can exceed state and federal safety standards. That could require costly upgrades or chemicals to counteract the algae bloom.
So take the must and the dust, calm the masses, and churn, baby, churn!