Beaver district keeps eye on water quality

An annual event in which volunteers fan out in boats to help Beaver Lake overseers test water quality provides a snapshot of water clarity, nutrient levels and algae content, but it will be years before the testing will yield meaningful, long-term results, officials there said.

On Friday, the Beaver Water District released the results of its 2012 Secchi Day, which was held on Aug. 18 and was its seventh annual such event since 2006.

This year 33 volunteer teams worked 35 sampling sites in their quest to sink little testers into the water and draw bottled samples.

Launch sites were Hickory Creek, Prairie Creek, Rocky Branch and Lost Bridge.

Besides clarity, levels of nitrate, phosphorus and chlorophyll were tested.

Beaver Lake is the primary drinking-water source for one in eight Arkansans, water district spokesman Amy Wilson said.

Bob Morgan, the district’s manager of environmental quality, said Kent State University has held a national Secchi Day for years, and there is a story behind the name.

In 1865, the pope asked a priest and scientist named Pietro Angelo Secchi to measure the clarity of the Mediterranean Sea. So he invented the Secchi disk.

“It was real clever, because they didn’t have the technological instruments we have today,” Morgan said.

Yet the low-tech disk still holds up, perhaps because of its simplicity.

The easy-to-use device is lowered into the water. The point at which it disappears from view is used as a measure of the water’s clarity, or transparency.

A normal Secchi depth would be a little more than 3 feet at Beaver Lake’s headwaters and about 18 feet to about 20 feet at Beaver Dam.

“If I was to measure in the headwaters of the lake, and I got a measurement of

1 [6/2 feet] I’d be very excited,” Morgan said. “But if I got the same measurement at the dam, I’d think a disaster had happened.”

Disaster could mean too many nutrients, or too much turbidity. Secchi Day volunteers also take Beaver Lake water samples to measure for those.

Secchi depth results this year found the lake “exhibited a slight gradient of increasing Secchi depth from its headwaters to the dam.”

The lowest reading was a little more than 1 foot at War Eagle Arm and the highest reading was about 18 1/2 feet at the dam, which is within normal range by Morgan’s numbers.

Beaver Lake flows north, he said, as he points out a map on the study results from this year.

“The first thing we can see ... when you start measuring the Secchi depth at the headwaters, which are near Fayetteville, and you work downstream to the dam, by Eureka Springs, you see it gets progressively clearer as you work your way down.”

He added: “That’s not surprising at all. That’s what you expect to see in a reservoir.”

Turbidity is another measure.

“It’s kind of the opposite of clarity,” Morgan said. Simply put, the turbidity is a measure of the water’s murkiness, in which a water sample is tested to see how well light scatters when it hits the sample.

August is the perfect time of year to test the water, Morgan said. That’s because there is less sediment present then, and sediment could confuse, or literally muddy up, the various results.

The district will need more than a decade’s worth of results before it will have enough meaningful data to identify long-term patterns in water quality, Morgan said. As it stands now, weather changes from one year to the next can cause significant changes that mask any long-term natural patterns.

The first seven years have mostly been laying the foundation: “We’re doing the base line,” he said. “Fifty years would be even better than 10 years. We just need lots of years.”

For instance, he said, drastic weather changes in recent years have been fodder for theories and a bit of confusion as well.

“One thing that we can see in the data this year” is how the drought stacks up compared with some recent years of heavy rains, he said.

“2008 and 2011 were really wet, we had those big floods,” Morgan said.In each of those years, the average depth was about 7 feet, he said.

That compared with the dry years of 2006 and 2010, when the average depth was about 10 feet.

“This last year,” he said of 2012, “we’ve had a real drought, and something that’s kind of confusing when I look at thedata is that the average Secchi depth is only [8 1/2 feet].

“We would have expected, because it’s such a dry year, that it would have been a little more clear,” he said. One theory at the district is that the 2011 flooding moved lots of nutrients into the lake and a corresponding low generation of electricity by the U.S. Army Corps of Engineers that year didn’t flush out as many nutrients as otherwise would have occurred.

“Chlorophyll a” is a pigment in algae used to measure the density of the lake’s algae population, according to the results, which showed concentrations appear to have been fluctuating in two- to three-year cycles ever since the testing began in 2006.

One nutrient that promotes algal growth, phosphorus, appeared to be on the decline this year from the headwaters to the dam in terms of “total phosphorus.” The latter term covers organic, dissolved inorganic and particulate inorganic phosphorus. Common sources are sewage, detergents and fertilizer runoff.

Another nutrient that encourages algal growth is nitrate. Nitrate is synonymous with the form of nitrogen that plants use. Common sources are leaking septic tanks, animal wastes, fertilizer runoff and car exhaust discharge.

This year, nitrate concentrations appeared to be on the increase from Prairie Creek to the dam, according to the Secchi studies.

Northwest Arkansas, Pages 9 on 12/22/2012

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