After eight years of collecting water quality data on Beaver Lake during the annual Secchi Day event, it’s possible to make some statistical comparisons. But it’s too soon to state with any confidence whether the lake is improving or degrading, according to Dr. Bob Morgan, Manager of Environmental Quality for Beaver Water District.
Thirty teams of volunteer citizen scientists sampled 35 sites, most in duplicate, on Saturday, Aug. 17th. Teams collected water samples and conducted Secchi depth measurements. Secchi depth is a measure of water transparency that involves lowering a black and white disk into the water and recording when the disk is no longer visible. The 2013 Secchi Day report is available on the District’s website at http://www.bwdh2o.org/education-and-outreach/events/secchi-day/.
This year, the greatest Secchi depth of 5.5 meters, or approximately 18 feet, occurred near Quarry Cove. The lowest depth of .3 meters, about 1 foot, was measured at the confluence of the White River and Richland Creek. In addition to Secchi depth readings, teams collect water samples that are analyzed by Beaver Water District’s lab technicians. The technicians measure chlorophyll a, total phosphorous, and nitrate in each of the water samples. Chlorophyll a is a pigment in algae that is used to measure the density of the algal population in water. Phosphorous and nitrate are both nutrients that promote algal growth.
“What we can say with statistical confidence is that the average Secchi depth measurement during drought years, in 2006 and in 2012, is significantly higher than those measurements made during flood years, 2008 and 2011,” Morgan said. “We can also say with statistical confidence that Secchi depth in late August in Beaver Lake is inversely related to the concentration of chlorophyll a (i.e. Secchi depth goes down as chlorophyll a goes up). This means that the transparency of water in Beaver is negatively affected by the amount of algae in the water. These data are consistent with the scientific literature on reservoirs and a confirmation that our citizen science is working.”
Secchi Day on Beaver Lake is made possible by 11 partners including Audubon Arkansas, Beaver Water District, the U.S. Army Corps of Engineers-Beaver Lake, the U.S. Geological Survey, the University of Arkansas Cooperative Extension Service, Hobbs State Park, Arkansas Master Naturalists, the Association for Beaver Lake Environment, Beaver Watershed Alliance, Arkansas Game & Fish Commission, and Ozarks Water Watch. Secchi Day is one of the premiere water public awareness and education events in Arkansas. Next year’s event will be held on Aug. 16, 2014.