Iowa Lakes Survey
Summer 2000 Data

John A. Downing

Joy M. Ramstack

Department of Animal Ecology

Iowa State University

January 2001

            The objective of the Iowa Lakes Survey is to sample 132 of Iowa’s principle recreational lakes, and to characterize water quality over a five-year period.  The following data represent the first of five years of sampling of these lakes.  One hundred and fifteen of the lakes were previously studied, and classified for restoration, by Roger Bachmann of Iowa State University in 1979 and again between 1990 and 1992 (Bachmann et. al, 1980; Bachmann et. al, 1994).

            A five-year study window was chosen because a single year’s data can be very far from average conditions (Bachmann et al, 1994).  Therefore, divergence of this year’s data from previous years may be substantial, even if conditions have remained similar.  There is probably even more inter-annual variation in Iowa lakes than seen elsewhere because of land disturbance and extreme nutrient conditions.  In the summer of 2000, rainfall in June and July was close to or above normal (2.29 and 0.04 inches (5.82; 0.10 cm) above normal in June and July, respectively).  However, the end of the summer was much drier (1.13 and 1.68 inches (2.87; 4.27 cm) below normal in August and September, respectively) (Iowa Department of Agriculture and Land Stewardship, State Climatologist’s Office, 2000).  Due to the great temporal variation in Iowa lakes, we suggest refraining from comparisons between this first year’s data and others, as such comparisons could be misleading.

            The 132 study lakes (Appendix 1) were each sampled three times during the summer of 2000, between June 12 and September 12.  Sampling was begun later than it will begin normally because study funding was not secured until May 2000, and equipment and supplies had to be ordered at this time.  Sampling was conducted at the deepest point in each lake basin, as determined by sonar and existing bathymetric maps, and the spatial locations of sampling points were recorded using GPS.  YSI’s 6-Series, Multi-parameter Water Quality Monitors were used in the field to collect profiles of temperature, dissolved oxygen, specific conductivity, pH, turbidity, and chlorophyll.  As these probes were lowered through the water column, the depth of the thermocline was determined (if one was present).  After the depth of the thermocline was determined, an integrated column sampler (which consisted of plastic tubing, weighted on one end, and calibrated in meters) was used to collect water from the upper mixed zone of the lake.  If no thermocline was present, then the entire water column was sampled.  The water from the column sampler was placed into a bucket, thoroughly mixed, poured into polypropylene bottles, and kept cold until it was delivered to the laboratory for analysis the next day.  This method was used to collect water samples for analysis of nutrients, phytoplankton (with Lugol’s solution added as a preservative; American Public Health Association, 1998), chlorophyll, and suspended solids.  Zooplankton samples were collected by vertically towing a Wisconsin net (63 μm mesh size) through the upper mixed layer of the lake (or through the entire water column if no thermocline was present).  Samples were transferred to a polypropylene bottle with distilled water, and Formalin (5% solution, with sucrose added) was added as a preservative.

            Every effort was made to accurately determine the depth of the thermocline in the field.  After generating graphs of the data, however, there were a few cases where the decision made in the field did not accurately reflect the depth of the upper mixed layer.  In the following data tables, the depth of thermocline reflects the decision that was made in the field because this represents the depth from which samples were collected.  Graphs of water depth and temperature are provided to visualize thermal structure.

Phosphorus, nitrogen, and silica analyses were performed on an HP 8453 Spectrophotometer, using standard water-analysis methods.  Phosphorus, ammonia, and silica analyses were performed according to Standard Methods (American Public Health Association, 1998), using Hach chemicals and protocols.  Phosphorus analyses followed the ascorbic acid method, with persulfate digestion (American Public Health Association, 1998), and silica analyses followed the molybdosilicate method (American Public Health Association, 1998).  Nitrate and total nitrogen were analyzed using second derivative spectroscopy (Crumpton et. al, 1992).  Laboratory analyses of chlorophyll a were performed on a Gilford Response Series UV-VIS Spectrophotometer, with acetone and magnesium carbonate extraction (American Public Health Association, 1998).  Methods used were substantially identical to those employed by Bachmann et. al (1980; 1994).  Quality assurance/quality control procedures were routinely employed; calibration standards and blanks were run with each set of samples.  Phosphorus, nitrogen, and silica samples were run in triplicate, with samples rerun if the level of replication was not within 20%.

The field measurements of chlorophyll were determined by fluorometry.  This method may be susceptible to interference by suspended particles in the water column, and provide an inaccurate measurement of chlorophyll.  Therefore, in the following chlorophyll profiles, the scale (in μg/l) should be disregarded and these profiles should be interpreted as a relative amount of chlorophyll in the water column.  Chlorophyll data in the tables are accurate and were determined using standard lab methods.

Phytoplankton and zooplankton samples are currently being processed and these data will be incorporated into future reports.

The following report is arranged alphabetically by lake name.  There are data tables of field measurements and water chemistry for each lake; data are reported for each of the sampling dates as well as a summer average.  In the data tables, “--“ denotes a missing value (or absence of a thermocline), usually due to sample loss or destruction.  For each lake, there are depth profiles of temperature, dissolved oxygen, specific conductivity, pH, turbidity, and chlorophyll, for each of the sampling dates.  Deer Creek Lake in Plymouth County was drained in the summer of 2000; this is the only lake of the 132 that was not sampled during this summer’s work.        

References

American Public Health Association, American Water Works Association, and Water Environment Federation. 1998. Standard Methods for the Examination of Water and Wastewater, 20^th ed. American Public Health Association, Washington, D.C.

Bachmann, R.W., M.R. Johnson, M.V. Moore, and T.A. Noonan. 1980. Clean lakes classification study of Iowa’s lakes for restoration. Iowa Conservation Commission.

Bachmann, R.W., T.A. Hoyman, L.K. Hatch, and B.P. Hutchins. 1994. A Classification of Iowa’s Lakes for Restoration, Iowa Department of Natural Resources, final report.

Crumpton, W.G., T.M. Isenhart, and P.D. Mitchell. 1992. Nitrate and organic N analyses with second-derivative spectroscopy. Limnology and Oceanography, 37(4), 907-913.

Iowa Department of Agriculture and Land Stewardship, State Climatologist Office. Iowa Climate Review. 2000. v14(6-9).

Acknowledgements

             We would like to acknowledge and thank all of the field and laboratory personnel who helped with the project this year.  Mike Barker, Mike Cummings, Nick Schlesser, and Kevin Schulte did an excellent job as the field crews for the project.  Amy Pogge was instrumental in organizing the laboratory aspects of the project, and Alissara Reungsang performed many of the laboratory analyses.  Jean Fitzpatrick, Ben Herman, and John Schomberg also helped with the laboratory analyses.  Nicole Eckles and Becky Cordes helped to train and supervise laboratory personnel, and assisted with a great deal of the laboratory work.  Jeff Kopaska was responsible for the initial organization and planning of the project.  Jamie Anthony helped to solve problems that arose in the field and the laboratory.  Carol Elsberry provided administrative support for the project.  Thanks to Terry Mayberry who flew to the field sites each morning to pick up samples, and the Department of Aerospace Engineering at Iowa State, who let us use their airplane.  Ramesh Kanwar and the Iowa State Water Resources Research Institute provided us with additional laboratory space.