You don’t miss your water — till it turns toxic
On Aug. 2, half-a-million residents of Toledo, Ohio were told to quit drinking city water that was laced with microcystin, a toxin produced by a carpet of blue-green algae in Lake Erie, Toledo’s water source. after concentrations dropped, the water ban that put the long-simmering problem of harmful algal blooms in the headlines was lifted on Aug. 4.
The shutoff was a public wake-up call about the harm of allowing lakes to get too fertile, but it was no surprise to experts who have long warned that excess plant nutrients in freshwater can feed blooms of toxic algae, properly called cyanobacteria. Agriculture, development and population growth are all stressing freshwater, which is so essential that the search for life in space concentrates on planets warm enough to have liquid water.
Ohio is remembered for the highly polluted Cuyahoga River, which caught fire in Cleveland in 1969, helping set the stage for the Clean Water Act in 1972. The Act was highly effective for cleaning up “point sources” like factories and sewage treatment plants, says Katrina McMahon, an associate professor of civil and environmental engineering and bacteriology at the University of Wisconsin-Madison. “In the United States, we assume that we fixed all the major water quality problems in the first round of responses to the Clean Water Act. We did a good job of cleaning up point sources, and have spent billions to trying reduce phosphorus concentrations [from them], but we haven’t spent nearly as much on non-point sources like fertilizer from farm runoff and manure from feedlots.”
HAB a nice day!
Toledo’s problem was, in the jargon, a harmful algal bloom (HAB). The toxin in question, microcystin-LR, is toxic to the liver; but HABs can also create nerve toxins and many other poisons. These toxins may be hazardous on contact, or when inhaled or ingested. Even blooms of non-toxic “nuisance algae” can annoy swimmers and boaters, or change the ecosystem by blocking sunlight or depriving water of oxygen as they decay.
Although do-not-drink orders are rare, outbreaks of cyanobacteria and other HABs are widespread in the United States, China and Europe. HABs are one common aspect of eutrophication – a complicated process of decline initiated in large part by over fertilization.
The long-term-trend is toward greater eutrophication, says Todd Miller, assistant professor of in the school of public health at UW-Milwaukee. “A well-cited study, Eutrophication of U.S. Freshwaters: Analysis of Potential Economic Damages, Dodds et al, Environ. Sci. Technol., 2009, 43 (1), pp. 12–19, looked at the environmental cost of eutrophication, which we can use as an indicator for the occurrence of cyanobacteria” in lakes like Erie that are shallow and warm in summer. “They find an overall increase in number of lakes and rivers classified as eutrophic over the last two or three decades.”
Some of the concern about toxic algae results from a combination of more effort and better analytical equipment, Miller acknowledges. “But there is a general sense that we detect toxins more frequently and detect new toxins that we have not seen before. Part of it is that we are looking more, and part is that they are becoming more widespread.”
Cyanobacteria, some of the oldest living organisms, have evolved into countless strains with differing toxicity. The most common toxin, microcystin-LR, “appears to be one of the most toxic forms,” says Miller, “and we primarily target that.” With so many genes making toxins, “There are 300,000 possible microcystin toxins.”
So far, Toledo has focused on microcystin-LR, but the potential diversity raises the cost of monitoring and treatment. “Cyanobacteria are like little pharmaceutical factories, and they make other compounds that have bioactive effects,” Miller says. “Some that we are detecting in (Wisconsin’s) Lake Winnebago have been explored for drug treatment… such as microginin, which is being considered for blood pressure reduction.” We remarked that this sounded, well, a bit healthier than a liver toxin, but Miller responded, “Do you want that in your drinking water? You’d rather get it from a doctor on a prescription.”
P stands for problem
If cyanobacteria cause myriad problems – endangering swimmers, harming wildlife, ruining drinking water – the options for prevention focus on reversing the tide of plant nutrients flowing from sewage treatment plants, lawns and especially farms. Scientists long debated the roles of the critical nutrients nitrogen and phosphorus in HABs, but today’s consensus focuses on phosphorus. “There was a lot of research in 1970s that showed if a lake was nutrient-poor, when you stimulated it with nutrients, you did not get algae unless you added phosphorus,” says Richard Lathrop, an honorary fellow at the Center for Limnology at UW-Madison. “It’s the limiting nutrient.”
Eventually, however, nitrogen may play a bigger role, Lathrop adds. “Sometimes really fertile lakes have so much phosphorus that algae doesn’t need more, and then the algae are limited by light or nitrogen.” Still, Lathrop says, most management efforts “are geared toward phosphorus, as it’s proven to be the nutrient that caused the lake to become fertile, and nitrogen is a little harder to control.”
Like an unwanted guest, phosphorus, once in a lake, tends to stay around for decades. In shallow lakes like Erie, which warm quickly in the summer, toxic cyanobacteria can explode and release a variety of toxins. A similar problem plagues much smaller lakes. Lake Winnebago in Wisconsin, for example, supplies water to the nearby cities of Neenah, Menasha, Oshkosh and Appleton.
Miller has measured 10-fold changes in the concentration of toxin in Lake Winnebago within 12 hours, as wind and water turbulence affect their abundance. Gas chambers in cyanobacteria inflate during the day to take advantage of sunlight that drives photosynthesis.
Toledo’s toxic troubles have raised the local profile of toxic algae, Miller says. “The public has gotten somewhat concerned, because Lake Winnebago is very similar to Lake Erie, and both have problem with excess nutrients, especially phosphorus, from agriculture.”
There are no federal standards for HAB toxins in freshwater, but the liver toxin microcystin-LR has appeared above 2000 micrograms per liter in Lake Winnebago. Another cyanobacteria product, the potent neurotoxin anatoxin-A, occurs at much lower concentrations.
The water supply plants in the four cities use filtering, treatment with ozone or ultraviolet light and chlorination, and Miller and his colleagues are testing which methods or combinations work best on several toxins. They have found that these treatments appear to be holding microcystin-LR below the World Health Organization drinking water standard of 1 microgram per liter.
Despite the headlines from Toledo, Miller says, “there is no mandate to test for microcystin in the drinking water, there is no budget to do that. I am unaware of any regular monitoring for microcystins or other algal toxins in the lake or finished drinking water other than what we are doing.”
Getting a better handle on the growth and movement of cyanobacteria is part of a Clean Lake Alliance project on the shore of Lake Mendota, in Madison, Wis. “We focus on near shore water quality,” says Katie Van Gheem, watershed engagement coordinator for the non-profit environmental organization. The 44 volunteers “sample at the end of the pier or where they can get knee deep in the water at beaches or parks. They look at water clarity, temperature, the presence of cyanobacteria, total phosphorus, the height and direction of waves.”
Most volunteers live along the lakeshore, Van Gheem says, and “are really interested to see how the clarity changes — is it clear or murky?”
Although Lake Mendota does not supply drinking water, it is eutrophying and contains cyanobacteria. The lake is called the “best studied lake in the world” due to the presence of the world’s first department of limnology (freshwater science) on the shore at UW-Madison.
The Clean Lake project aims to fill gaps in other efforts that sample other parts of the lake, says director of policy and communication Elizabeth Katt-Reinders. “We are interested in better understanding how harmful algae blooms form and move, and so we need to know more about the near shore locations.”
Progress, or holding the finger in the dike?
Despite programs and grants to reduce phosphorus, control non-point pollution and combat eutrophication, levels have not fallen in Mendota and its watershed, says Lathrop, who is an authority on a well-studied lake. “Progress has been made, but the frustrating part is it seems like things are about the same in the lakes.”
The sense of treading water is unmistakable. In the Lake Mendota watershed, Lathrop says, “More manure is being generated, each farm is getting bigger, they are confining cows so they have more head of cattle on the same size farm, and producing more manure that they don’t have the land base to dispose of responsibly, so there is a lot of runoff of soil that’s been enriched by manure.”
Aiding the fight against phosphorus are two large manure digesters, where microbes digest manure and make methane, which is burned for electricity. The liquid is drained off, leaving phosphorus concentrated in the dry, light solids that are easy to transport so they can be spread as fertilizer. “Now we can take it to a field that is lower in phosphorus,” Lathrop says. “Historically, fields close to the farms are overloaded with phosphorus.”
All other things being equal, higher levels of phosphorus in the soil equate to more runoff.
The digesters reduce wintertime spreading of manure, when it’s likely to run off into streams, Lathrop adds. “We can put it on when its warmer, and it will stay with the soil. The digesters, together with no-till planting, buffer strips and cover crops, do a better job of keeping the soil in place, but if you keep adding more fertilizer and manure to the land,” phosphorus runoff will not drop.
“In the Yahara watershed, the technology is there, the best management practices are there, but they are not being implemented where they need to be,” says McMahon, an expert on toxic algae. “Partly it’s financial. Making a change to the operation is expensive, or is perceived as expensive. It’s also culture. For a few, the attitude is, ‘DNR or county, you don’t tell me what to do. This was my grandpa’s farm; he did it this way, and we still do it that way.’ A lot of folks are engaging, but the few bad apples are super emitters, and until you can convince them to change, it’s hard to make a difference.”
Shall we cooperate?
Given opposition by the agricultural and fertilizer industries, nutrient regulation seems unlikely, leading to the testing of dozens of voluntary programs to reduce over-fertilization. A key selling point: phosphorus is costly, and there’s no sense wasting money on unneeded fertilizer.
“We are having great success building relationships with farmers, having them look at conservation practices and water quality as components of their farming practices,” says Katt-Reinders of the Clean Lakes Alliance. “An affiliate, Yahara Pride Farms, is led by farmers who adopt this brand that is synonymous with practices that protect water quality. They are trying to make a business case for conservation, trying to run a profitable farm while adapting practices to be more protective of water.”
Farmers get certified into the program after a crop and soil assessment, and a conversation with a farm conservationist. Certified farms are eligible for cost-sharing for contour and conservation tillage, and injection and composting of manure.
Warming and storming
So far, phosphorus reductions are being seen in streams near farms, but not yet in Lake Mendota, and the struggle continues. Despite use of good management to keep phosphorus in the soil, the intensifying rainstorms due to global warming are having an effect. “If we have a 200-year flood every couple of years, that washes a lot of soil into the lake that normally would not have washed in,” says McMahon. “A lot of phosphorus is stored in the watershed, and in one big flood, it all ends up in the lake.”
The efforts to reduce phosphorus pollution from agriculture and other sources are “confounded by climate change and a lack of patience,” says McMahon. “There is so much phosphorus in the soil and it takes a long time for it to work its way out of the system.”
It’s the same story in the lakes, she McMahon adds. “It’s in the nature of eutrophication. You have put a lot of nutrients in the lake and they are recycled year after year. With phosphorus, as with cyanobacteria, there is no quick fix.”
– David J. Tenenbaum