Long-term citizen-collected data reveal geographical patterns and temporal trends in lake water clarity.
We compiled a lake-water clarity database using publically available, citizen volunteer observations made between 1938 and 2012 across eight states in the Upper Midwest, USA. Our objectives were to determine (1) whether temporal trends in lake-water clarity existed across this large geographic area and (2) whether trends were related to the lake-specific characteristics of latitude, lake size, or time period the lake was monitored. Our database consisted of >140,000 individual Secchi observations from 3,251 lakes that we summarized per lake-year, resulting in 21,020 summer averages. Using Bayesian hierarchical modeling, we found approximately a 1% per year increase in water clarity (quantified as Secchi depth) for the entire population of lakes. On an individual lake basis, 7% of lakes showed increased water clarity and 4% showed decreased clarity. Trend direction and strength were related to latitude and median sample date. Lakes in the southern part of our study-region had lower average annual summer water clarity, more negative long-term trends, and greater inter-annual variability in water clarity compared to northern lakes. Increasing trends were strongest for lakes with median sample dates earlier in the period of record (1938-2012). Our ability to identify specific mechanisms for these trends is currently hampered by the lack of a large, multi-thematic database of variables that drive water clarity (e.g., climate, land use/cover). Our results demonstrate, however, that citizen science can provide the critical monitoring data needed to address environmental questions at large spatial and long temporal scales. Collaborations among citizens, research scientists, and government agencies may be important for developing the data sources and analytical tools necessary to move toward an understanding of the factors influencing macro-scale patterns such as those shown here for lake water clarity.
Center for Limnology Trout Lake Station, University of Wisconsin Madison, Boulder Junction, Wisconsin, United States of America.
Noah R
NR
Lottig
U.S. Geological Survey, Pennsylvania Cooperative Fish and Wildlife Research Unit, Pennsylvania State University, University Park, Pennsylvania, United States of America.
Tyler
T
Wagner
Department of Fisheries and Wildlife, Michigan State University, East Lansing, Michigan, United States of America; Department of Outreach and Engagement, Oregon State University, Tillamook, Oregon, United States of America.
Emily
E
Norton Henry
Department of Fisheries and Wildlife, Michigan State University, East Lansing, Michigan, United States of America; Lyman Briggs College, Michigan State University, East Lansing, Michigan, United States of America.
Kendra
K
Spence Cheruvelil
School of Natural Sciences, Trinity College, Dublin, Ireland.
Katherine E
KE
Webster
Department of Ecology, Evolution, and Organismal Biology, Iowa State University, Ames, Iowa, United States of America.
John A
JA
Downing
Great Lakes Environmental Research Laboratory, National Oceanic and Atmospheric Administration, Ann Arbor, Michigan, United States of America.
Craig A
CA
Stow
D003625:Data Collection / Q000379:methods*; D005843:Geography; D060106:Lakes; D015146:Midwestern United States; D060753:Water Quality