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Iowa Lakes SurveySummer 2001 Data
John A. DowningJoy M. Ramstack Department of Animal Ecology
Iowa State UniversityJanuary 2002
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 second of five years of sampling of these lakes (averages from the summer of 2000 are also included in the data tables). 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). 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 was 2.29 inches (5.82 cm) above normal in June, and 0.04 inches (0.10 cm) above normal in July. 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). In the summer of 2001, the beginning of the summer was wet (average rainfall in May was 3.05 inches (7.75 cm)). However, rainfall was below average for the remainder of our sampling months in 2001 (0.29, 0.92, and 1.05 inches (0.74, 2.34, and 2.67 cm) below normal in June, July and August, respectively) (Iowa Department of Agriculture and Land Stewardship, State Climatologist’s Office, 2001). The 132 study lakes (Appendix 1) were each sampled three times during the summer of 2001, between May 14 and August 9. 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. Ammonia, and silica analyses were performed according to Standard Methods (American Public Health Association, 1998), using Hach chemicals and protocols. Silica analyses followed the molybdosilicate method (American Public Health Association, 1998). Phosphorus analyses were performed in accordance with Standard Methods and followed the ascorbic acid method, with persulfate digestion (American Public Health Association, 1998). Nitrate and total nitrogen were analyzed using second derivative spectroscopy (Crumpton et. al, 1992). For the first round of samples (collected between May 14 and June 7), 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). Samples that were collected between June 11 and August 9 were analyzed in the laboratory for chlorophyll a on a Turner Designs TD-700 Laboratory Fluorometer, with acetone and magnesium carbonate extraction (American Public Health Association, 1998). We switched to a fluorometric method for measuring chlorophyll a in the laboratory to increase precision. 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. Fluorometry that is performed in the field may be susceptible to interference by suspended particles in the water column, and provide an inaccurate measurement of chlorophyll. Therefore, the following chlorophyll 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. During the summer of 2001, lake water samples (taken as an integrated sample from the mixed zone, or from the entire water column when no thermocline was present) were also analyzed for a variety of pesticides during the second sampling round (between June 11 and July 12). All pesticide analyses were performed by the Hygienic Laboratory at the University of Iowa, following standard EPA approved methods. All of the lakes were analyzed for 11 nitrogen containing herbicides. A subset of 36 lakes was also analyzed for organophosphate insecticides, acid herbicides, polychlorinated biphenyls, chlorohydrocarbon insecticides, and an additional 6 nitrogen containing herbicides. The following report is arranged alphabetically by lake name. Data tables of field measurements and water chemistry are presented for each lake; data are reported for each of the sampling dates, with a summer average for 2000, as well as the summer average from 2001. In the data tables, “--“ denotes a missing value (or absence of a thermocline), usually due to sample loss or destruction. No averages are provided in the case of sampling depth and thermocline depth, whereas such averages were deemed of little meaning. 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 and Williamson Pond in Lucas County were both dry during the summer of 2001; these are the only lakes of the 132 that were 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, 20th 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). Iowa Department of Agriculture and Land Stewardship, State Climatologist Office. Iowa Climate Review. 2001. v15(5-8). Acknowledgements We would like to thank everyone who assisted with the Iowa Lakes Project this year. Becky Cordes, Nicole Eckles, Kendra Lee, and Kristian Haapa-aho managed the laboratory and supervised summer employees. Melissa Millman, Polly Ready, Jen Durham, and Emily Brown performed many of the laboratory analyses and helped to organize laboratory aspects of the project. Mike Cummings, Jacob Huck, Ben Hucka, David Schelling, and Nicholas Schlesser performed all of the field work associated with the project. Christy Cherrier and Ben Dodd assisted in the laboratory and have been working with the biological samples. Carol Elsberry provided administrative support for the project. Jamie Anthony and Jeff Kopaska helped to solve problems that arose in the field and the laboratory. Ryan Castro provided computer support for the project. Terry Mayberry flew to the field sites each morning to pick up samples, and the Department of Aerospace Engineering allowed us to use their airplane. Ramesh Kanwar and the Iowa State Water Resources Research Institute have provided us with additional laboratory space over the course of the project. Lakes
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