UNIVERSITY PARK, Pa. -- A study of water clarity in Midwest lakes during a 70-year period that spanned passage of the Clean Water Act reveals a steady improvement over time, according to a researcher in Penn State's College of Agricultural Sciences.
The research was unique because it analyzed nearly a quarter of a million observations taken over a period of 70 years on 3,251 lakes in eight Midwestern states by citizen scientists -- lakefront homeowners, boaters, anglers or other interested members of the public wanting to know a little more about what's going on in "their" lake.
Study co-author Tyler Wagner, adjunct associate professor of fisheries ecology and assistant leader of the Pennsylvania Cooperative Fish and Wildlife Research Unit at Penn State, noted that ecologists increasingly are looking at big-picture issues, such as how changes in land use or climate affect ecosystems at a state, national or even continental scale.
"There aren't enough scientists in the world to collect data for these projects," he said. "But, thanks to citizen scientists, there's a lot of information out there. Really, citizen data has been underutilized."
Wagner and a team of freshwater scientists from across the United States combed through state agency records and online databases of water-clarity measurements taken by nonscientists using a circular, plate-sized instrument called a Secchi disk.
Used in aquatic sciences since the mid-1800s, Secchi disks hang from a rope and are lowered into the water until their distinct black and white pattern disappears from view, a distance that marks the "Secchi depth." Lake associations and other citizen groups have used the disks for decades to document conditions on their waters.
"Previous studies have shown that citizen Secchi readings are nearly as accurate as professional scientists' measurements," said Wagner. "With a dataset covering more than 3,000 lakes and stretching back to the late 1930s, we were able to look for long-term changes in water clarity over a large area."
In the study, which was published in the April 30 online issue of PLOS ONE, researchers examined water-clarity measurements before and after passage of the Clean Water Act, which was signed into law in 1972. The act set water quality goals for all U.S. waters.
"Thanks to the data collected by citizen scientists during decades both before and after the Clean Water Act came into effect, we thought we might detect a landscape-scale shift over time to clearer water -- indicating cleaner water," Wagner said.
"What we found was a 1 percent average annual increase in water clarity across all lakes. However, there was considerable variability in water-quality trends among individual lakes."
For example, many lakes were relatively stable in water clarity over time, and most of the increases in water clarity occurred in lakes at more northern latitudes, in states such as Minnesota and Wisconsin. In fact, some lakes at the southern portion of the study area have long-term declining trends in water clarity.
"We expect that much of the north-south gradient in water clarity is related to land use and climate," Wagner said.
He believes the study demonstrates that citizen science can play an important role in shaping future research -- a sentiment shared by the National Science Foundation.
"This study highlights the research opportunities that are possible using data collected by citizens engaged in making important environmental measurements," said Elizabeth Blood, program director for the NSF's Directorate for Biological Sciences. "Their efforts provide scientists with data at space and time scales not available by any other means."
Also participating in the study were the Center for Limnology, University of Wisconsin; Department of Fisheries and Wildlife, Michigan State University; Department of Outreach and Engagement, Oregon State University; Lyman Briggs College, Michigan State University; School of Natural Sciences, Trinity College, Dublin, Ireland; Ecology, Evolution, and Organismal Biology Department, Iowa State University; and theNational Oceanic and Atmospheric Administration, Great Lakes Environmental ResearchLaboratory.
The National Science Foundation funded the research.