Summer's end signals a shift in Beaver Lake some people can taste.
Blue-green algae, or cyanobacteria, grows in the lake all summer, said Bob Morgan, manager of environmental quality for Beaver Water District. The algae use up nutrients in the lake as the weather begins to cool and trigger a minor ecological crash. The blue-green algae die off and spill the strong-smelling compound inside known as 2-methylisoborneol.
Quality standards
Beaver Lake is the first lake in Arkansas to have site-specific standards mandated by state law for chlorophyll and secchi transparency, both used as indicators of algae levels. The chlorophyll measurement is the pigment of the algae. Secchi transparency is the depth at which a disc used to measure water clarity is visible. Volunteers measure both levels across the lake as part of Beaver Water District’s annual Secchi Day outreach.
A rough average of 8 parts per billion of chlorophyll measured across the May through October growing season is the Arkansas Department of Environmental Quality standard for Beaver Lake. Secchi Day 2014 readings measured the best near Starkey Marina with 1.59 parts per billion and the worst at the White River arm near the Arkansas 412 bridge with 20.03 parts per billion.
A 1.1 meter secchi depth as an annual average is the Arkansas Department of Environmental Quality standard for Beaver Lake. Secchi Day 2014 readings measured the best near Hall Spring Branch with a 3.61 meter reading and the worst at the confluence of White River and Richland Creek with a .58 meter reading.
Source: Staff report
"It takes an amazingly little amount of that to pass the threshold when you can taste it," Morgan said.
A sensitive palate could taste a single bucket of 2-methylisoborneol dumped into Beaver Lake, he said. He could smell it faintly in the water last week.
Beaver Water District supplies much of Northwest Arkansas with purified water from the lake.
Algae settle out in tanks at the water treatment facility or are stripped out of the water in sand filters. A disinfection process kills off pathogens, but the smell sticks.
All water can have a different makeup of minerals and organic chemicals, which will make the taste vary, Morgan said.
"Spinach is not detrimental to your health, but it has flavor," he said.
The taste left behind in the water isn't a concern, but keeping the lake balanced so algae do not grow unchecked is, scientists said.
You can almost set your watch on a Labor Day taste and odor event, said Thad Scott, assistant professor of environmental sciences at the University of Arkansas Fayetteville.
"I can't taste it at all," said Scott, who studies lakes.
Drinking water intakes are close to the cities, but also close to the lake's shallow headwaters, Scott said. Water from the streams carries nutrients like phosphorus and nitrogen and feeds the algae. Algae take nutrients from the water and use sunlight to grow, much like trees take nutrients from the soil and use sunlight to photosynthesize, Scott said.
"Algae are good for sure. No algae, no fish," Scott said.
Algae form the base of the lake food chain, Morgan said. Zooplankton, the smallest creatures of the lake, feed off phytoplankton, the smallest plants. Small fish feed off the zooplankton, and the lake's bass eat a supply of smaller fish.
Algae are the pasture of the lake, said Reed Green, president of the North American Lake Management Society and hydrologist in the U.S. Geological Survey office in Little Rock.
It causes an imbalance if there are too many nutrients in the lake and algae grow quicker than the food chain consumes them.
There are toxic algae strains that can cause skin irritation, neurological damage and liver damage, Green said. Other states have seen outbreaks, but Arkansas' first meeting to discuss harmful algae blooms was held two weeks ago. A high concentration of toxic algae is a low risk in Beaver Lake, Morgan said. In places where it has been a problem there have been floating mats of algae. There isn't that much in the lake now, he said.
"It's not green pea soup," Morgan said.
Water quality would have to drop to allow for any problems, he said. Still, the water district will begin to run enzyme-linked immunosorbent assay tests next year that will detect any toxic algae.
Phosphorus feeds algae, Green said. Phosphorus is stored in silt, clay and other sediment that travel into the lake from eroding stream beds. Reservoirs like Beaver Lake trap between 60 to 80 percent of the sediment that flows in each year, Green said. That makes erosion a potential problem.
"If the stream bank fails and it's 6, 8, 10 feet above the water and 8 feet back into the pasture, how many dump trucks of sediment is that?" Green said.
The annual sediment load for the West Fork White River Watershed was estimated at 35,795 tons with 74 percent of that sediment coming from stream bank erosion, according to a 2004 report from the Arkansas Department of Environmental Quality.
Sediment doesn't go away. It builds up and as the summer warmth leaves the lake. When the colder water from the depths turn to the top, it belches up phosphorus, feeding algae, Green said.
Stopping erosion isn't enough because a problem in one part of the stream can trigger another. John Pennington, executive director of Beaver Watershed Alliance, is aiming for an $8.6 million project to help manage forest and pasture in 40 square miles of watershed on the West Fork of the White River. The project also would restore 2 miles of stream bank to its natural width to depth ratio and add natural grasses and trees to keep it that way. There are matching grants if he can get basic funding, Pennington said, but there is no fee through water bills to fund watershed protection.
Businesses depend on clean water, Pennington said. There could be an economic loss related to a drop in recreational use if the lake becomes prone to algae, Green said. There will be a cost to clean water now or later, Green said.
"They can treat ocean water and turn it into drinking water, but it's really, really expensive," he said.
Lake management plans can be put into place where chemicals strip phosphorus from the water, and there are herbicides that could kill off algae, but Beaver Lake is so large that those options would have to be targeted at specific areas, Green said.
Protecting the water will keep the cost down of getting it to the tap, he said.
Water that runs off a lawn ends up in a stream and everyone has a role to play, Morgan said. Simple things can help, like pulling a car onto the lawn for a wash so the grass can help filter the water.
"It's not 'them' that's causing it," Morgan said. "It's us that's causing it."
NW News on 09/08/2015