Teams of volunteers who headed out on Beaver Lake for the annual Secchi Day on Saturday were on a mission of citizen science. That is, to measure the reservoir's water clarity from one end to the other as they do each August.
The event gives water-quality officials at the Beaver Water District a lake-wide snapshot of water clarity on nearly the same day each August from year to year, said Bob Morgan, the district's manager of environmental quality. Beaver Water District treats water from the reservoir to provide drinking water to much of Northwest Arkansas and beyond. They're chief sponsor of Secchi Day.
Volunteers used Secchi Disks to take the measurements at 30 sites from the headwater of the lake near Fayetteville to Beaver Dam near Eureka Springs. Measurements were all taken at the same time.
A Secchi Disk is a black and white sinking disk that is lowered through the water column. When the disk is no longer seen in the water, volunteers note the depth on report sheets.
Clarity was a few feet or less in the headwater to 12 feet near the dam. Volunteers also took water samples that will be analyzed in the Beaver Water District lab. Educational events at Prairie Creek park on the lake are a major part of Secchi Day.
Secchi Day makes one thing perfectly clear. A number of factors affect water clarity from year to year, Morgan said.
The sky was cloudy Saturday morning and that can mean lower clarity measurements than on a sunny day. The amount of rainfall during summer can affect the measurements. The lake water is usually less clear during a rainy summer than a dry one, Morgan said.
Secchi Day measurements were generally lower this August than last, Morgan said, then showed data dating back to 2006.
Average clarity of all 30 sites in 2006 was 10.5 feet. "Then 2008 was a big flood year and the average dropped to 7.2 feet.," Morgan said.
Clarity improved the next two years until another flood in 2011 decreased clarity on Secchi Day that year.
Why do water officials need to know this? If clarity steadily deteriorates from year to year or other trends develop, it tells water professionals that steps need to be taken.
Families make up a number of the volunteer teams on Secchi Day. They give their measurement sheets to Beaver Water District officials, then take part in hands-on educational exhibits and lunch festivities.
Palika Morse and her husband, James Morse, made Secchi Day a teaching moment for their family. Their children and friends took part in an educational scavenger hunt and a quiz game. Other exhibits taught them about aquatic insects and causes of pollination.
"They're learning lots of things about the Beaver Lake watershed and water quality," Palika said.
Education opportunities at Secchi Day are as important as the water clarity measuring, said Mark Curtis, a board member with the Association For Beaver Lake Environment.
"It's extremely valuable from a scientific standpoint for the people of Northwest Arkansas. We are whole-heartedly behind this event," he said.
Outdoors on 08/17/2014