Environmental Microbiology and Bacteriology of Clear Lake, Iowa

 

John A. Downing and Nicholas Schlesser

 

Special Acknowledgment.  We would like to acknowledge the special financial assistance of the City of Clear Lake for portions of this analysis, as well as the willing help of many volunteers and city employees who collected samples for preliminary analyses leading to these microbiological studies.  Special action taken by the Mayor Kirk Kraft, City Manager Tom Lincoln and the entire City Council in August and September of 1998 was instrumental in stimulating this work.

 

A.        History.  

 

Bacteria are essential to the function of aquatic ecosystems and a natural part of the biota of all environments.  Certain bacteria, usually called “enteric bacteria” or “coliforms” enter aquatic systems from fecal matter produced by humans and other warm-blooded animals, and are thus used as indicators of potential disease-causing organisms in freshwaters.  Shallow, warm-water systems such as Clear Lake frequently receive coliform bacteria from the surrounding watershed during rain events, and the very rich nutrient and sediment environments found in eutrophic and hypereutrophic lakes allows these bacteria and probably the pathogenic bacteria to survive for relatively long periods.

 

It is quite likely that coliform bacteria have been found in Clear Lake and other Iowa lakes for quite a long time.  Analyses performed routinely by the University Hygienic Laboratory (UHL) on the intake water of the old Clear Lake city water system show frequent detections of coliform bacteria dating from as far back as records are available (i.e., early 1960s).  Therefore, fecal coliform bacteria have been a part of the Clear Lake environment for decades.

 

In the summer of 1998, however, a health incident precipitated the testing of the beaches of Clear Lake for coliform bacteria, and some high readings were detected.  Prior to this time there had been little routine beach testing by IDNR so beach closings were attempted as a reaction to these high levels.  Some of the samples were taken just following rain events, so some high values would normally have been expected.  As agencies acquired more information on fecal bacteria levels and testing protocols, however, it became clear that fecal bacteria levels were quite variable but that averaged measurements in Clear Lake were not consistently high.

 

Because of their concern for the well-being of Clear Lake and its safety as a recreational resource, Clear Lake City Council contracted intensive bacterial analyses of the lake, other lakes, and storm drain effluents to gauge the best route to efficient and effective remediation.  The sought to answer three questions: (1) How do coliform levels in Clear Lake compare to those found in other recreational lakes in the region? (2) Are storm drains a potential source of bacteria? (3) Do spatial analyses of bacteria in the lake indicate the greatest potential sources?  The City of Clear Lake has commendably already taken action toward using these data to reduce the City’s contribution of fecal bacteria to the lake.

 

The first question was approached by testing several Iowa beaches immediately following Labor Day weekend.  All showed levels of fecal coliform bacteria within the acceptable norms for recreational waters.  Clear Lake beaches were all in the high 25% of tested beaches, but were all within the acceptable range. Sampling was performed following the standard protocols indicated in Standard Methods for the Examination of Water and Wastewater.  Samples were taken in a way that represents the exposure of swimmers and other recreational users to lake water.  Five sets of samples were taken at each site, halfway between the surface and bottom in approximately three feet of water.  Samples were all taken on September 8, 1998, immediately following Labor Day weekend. The results below show the average level of fecal coliform bacteria found at each site. It should be noted that fecal coliform levels can vary greatly with time and are especially sensitive to rainfall events.

 

 

 

Concentrations

(CFUs/100ml)

 

 

 

 

Lake

Site

Rep. 1

Rep. 2

Rep. 3

Rep. 4

Rep. 5

Average*

Clear Lake

McIntosh Woods

50

70

20

50

<10

38

Rathbun Lake

Island View

10

<10

10

18

50

18

Clear Lake

City Beach

<10

<10

50

10

<10

12

Big Creek

beach

20

10

10

<10

<10

8

Clear Lake

State Park

20

10

<10

10

<10

8

West Okoboji

Gull Point

<10

<10

<10

30

<10

6

Rathbun Lake

dam beach

20

<10

<10

<10

<10

4

Storm Lake

beach

<10

<10

10

10

<10

4

West Okoboji

Terrace Park

10

<10

<10

10

<10

4

Spirit Lake

Marble Beach

<10

<10

<10

10

<10

2

Big Blue Quarry

Mason City

<10

9

<10

<10

<10

2

Spirit Lake

Crandall Park

<10

<10

9

<10

<10

2

Crystal Lake

beach

<10

<10

<10

<10

<10

0

Saylorville Lake

Sandpiper

<10

<10

<10

<10

<10

0

Spirit Lake

Orleans Beach

<10

<10

<10

<10

<10

0

Spirit Lake

Waterworks Beach

<10

<10

<10

<10

<10

0

West Okoboji

Arnolds Park

<10

<10

<10

<10

<10

0

West Okoboji

Emerson Bay

<10

<10

<10

<10

<10

0

West Okoboji

Pikes Point

<10

<10

<10

<10

<10

0

West Okoboji

Triboji Beach

<10

<10

<10

<10

<10

0

 

Federal standards for bacteria are exceeded when fecal coliform counts are greater than 200 colony forming units (CFU) per 100 mL of water.

 

The Ambient Water Quality Criteria for Bacteria - 1986 (USEPA, 1986) had the following recommendations for recreational bathing waters:

Based on a statistically sufficient number of samples (generally not less than five samples equally spaced over a 30-day period), the geometric mean of the E. coli concentrations should not exceed 126 per 100 mL.

Therefore, all Iowa beaches tested following a period of high use and low rainfall had acceptable levels of coliforms.  Clear Lake's beaches had among the highest levels, but were comparable to those found in Rathbun Lake, Big Creek Lake, and at West Okoboji's Gull Point Beach.

 

The second question (storm drain contributions of bacteria) was examined by applying a battery of diagnostic tests assess bacteria levels and attempt to discriminate animal fecal from human sewage bacteria.  Most input of fecal bacteria from storm drains would potentially occur shortly after runoff events.  Storm drain effluents were analyzed immediately after a storm-event on September 23, 1998.  Water samples were analyzed for bacterial constituents including fecal coliforms, Escherichia coli, and enterococcal bacteria.  The indicator-ratios of fecal coliforms/enterococci and E. coli/enterococci were calculated since higher ratios indicate that coliforms are likely of human origin.  Indicator chemical species including caffeine, nitrogen and phosphorus were also measured.  Data indicate that significant amounts of bacteria derive from storm drains and that materials of human origin are most abundant in lakeside storm drains between 7th Avenue South and 4th Avenue North near downtown Clear Lake, and along the north shore between Fareway Drive and Clark Road.  Isolated strong indicators were also present near the 2100 block of North Shore Drive.  Fecal coliforms of animal origin apparently dominate along much of the north shore between 5th Avenue North and Reely Point.  Notably, similar batteries of tests were not performed on county storm drains or those of the City of Ventura.  Based on storm drain nutrient data, it is quite likely that storm drains from other residential and commercial areas around the lake would yield similar conclusions.

 

1.         Methods

 

a.  Field collections.  Storm drain grab samples were collected by employees of the City of Clear Lake, and each storm drain outlet to the lake proper was sampled.  Employees were asked to catch the first flush of water through these systems for analysis.  Five samples were taken for microbiological analysis, and one sample for chemical analysis. Microbiological samples were collected directly into glass bottles provided by the University of Iowa Hygienic Laboratory (UHL).  These five samples were spaced at one-minute intervals.  A time-integrated sample was taken between filling the glass bottles, using a 20-liter chemically clean water container.  Some situations did not allow placement of the water container under the storm drain outfall, so a cleaned and modified one-gallon milk jug was used to collect the water sample and transfer it to the water container.  Care was taken to avoid contamination of the water samples with anything other than the effluent flowing from the outfall.

 

b.  Analytical methods.  We used standard protocols (APHA 1995, Hach Company 1992) to perform sample bottle and glassware preparation, sample preservation and laboratory procedures.  Steps taken for quality assurance and quality control included taking replicate water samples in the field and analyzing triplicate samples in the laboratory.  Assays using these protocols included pH, conductivity, chloride, total alkalinity, total-, volatile-, and inorganic-suspended solids and total phosphorus.  Specifically, pH and conductivity were measured directly using digital meters, chloride was measured by use of an ion-selective electrode, and total alkalinity was measured by titration. Total, volatile and inorganic suspended solids were measured by mass difference after filtration, evaporation and combustion of the sample. Total nitrogen assays were performed using the second derivative spectroscopy technique of Crumpton et al. (1992). Microbiological determinations of fecal coliform bacteria, E. coli and enterococci were conducted by UHL and followed the membrane filtration procedure with confirmation.  Total phosphorus was determined by spectrophotometry using the acid persulfate digestion, ammonium molybdate method, and all samples were run in triplicate for quality asurance/quality control purposes.  Caffeine analyses were performed by methylene chloride extraction and concentration followed by detection using a gas chromatograph / mass spectrometer.

 

2.  Results.  The analytical results of the storm drain samples are shown in Table 1.  Normally, storm drain water should be mostly composed of rainwater and the nutrient materials picked up as the water runs off of streets and lawns.  Most water therefore should be of neutral pH (ca. 7.0) or slightly lower; alkalinity and conductivity should both be low.  Clear Lake's storm drain water is extremely heterogeneous, reflecting diverse sources, including some higher alkalinity measurements that suggest that storm waters are mixed with ground water or pass through soils before they are discharged.

 

a.  Microbial Analyses.  Fecal coliform concentrations in storm drain effluent were high across the board.  No sample yielded concentrations lower than 2700 colony forming organisms per 100 mL of water sample (safe lake water must consistently have <200 colony-formers per 100 mL).  Highest concentrations of fecal coliforms were found in drains along the north shore, especially toward the western extreme of the city limits (Fig. 1).  A very similar pattern was seen in the concentrations of E. coli (Fig. 1).  Most of the fecal coliforms were probably natural enteric forms of E. coli.  Another group of bacteria derived from the digestive systems of all warm-blooded animals, the enterococci, also showed a very similar distribution among the storm drains along the north shore of the lake (Fig. 1). 

 

Because enterococci are less abundant in human sewage than in animal excrement, the ratios of fecal coliforms or E. coli to enterococci can be used to indicate human inputs.  Higher values of these ratios are typical of human sewage while most other animals would show lower ratios.  These ratios both show that human inputs are most likely in storm drains numbered 5-14 and 25-30 in Table 1.  These drains were located along the downtown waterfront and at the extreme west of the city, west of the Harborage.  Thus, bacterial inputs from storm drains were considerable, but downtown and extreme western drains were likely to have a human component.  Much of the bacteria between these areas probably derives from yard, animal and pet waste.  Concentrations of bacteria from all these drains are likely to contribute substantially to the bacterial concentrations seen in tests of lake water.

 

b.  Chemical Analyses.  Alkalinity measures the buffering capacity of water and is therefore a good indicator of how much contact there has been between drainage water and soil.  Several of the drains showed significant alkalinities (>20 mg/L; lakewater measures 130-150 mg/L).  Storm drains showing higher bacterial ratios had higher alkalinities indicating that these waters had been in contact with soil or have a groundwater or surface water component of 10-50%.  This could result from overflow of rivers, streams or holding tanks, or from the discharge of saturated groundwaters.  Chloride (Cl) is a conservative tracer of human sewage because salt (NaCl) is common in the human diet, relatively rare in the environment, and is not broken down or absorbed once it is dissolved.  Chloride measurements show probable human inputs around downtown Clear Lake, in drainage water near 33rd Street West, as well as near Reely's Point and near the Fish Hatchery (Fig. 2). 

 

Caffeine was analyzed because it is a reliable indicator of human sewage inputs.  Urinary caffeine levels in caffeinated soda drinkers (2 per day) are about 1500 mg/L (Bernardot 1996).  Considering that normal urine volume is an average 1400 mL/day, adult urinatation frequency is an average five times/day (Berkow 1977), and normal flush volume is about 2.6 gallons (9.8 liters), raw urinary sewage should contain about 41,000 ng/L of caffeine.  Our minimum analytical level for caffeine (40 ng/L) therefore can reliably detect raw sewage diluted up to 1000-fold.  The Mississippi River below the Twin Cities' sewage outfall contains about 70 ng/L of caffeine (Meade 1995) and therefore corresponds to about a 600-fold dilution of raw urinary sewage.

 

Caffeine was detected in all of the Clear Lake storm drains (Fig. 2).  Concentrations ranged from 24 to 780 ng/L (Table 1).  These concentrations correspond to sewage dilution rates of 50- to 1700-fold.  Highest caffeine concentrations were found clustered around downtown Clear Lake between 7th Street South and 1st Avenue North, and at the western extremity of Clear Lake's storm drain system between 33rd Street West 3800 block of North Shore Drive (Fig. 2).  An isolated high concentration was found in the 2100 block of North Shore Drive near Reely Point.  These areas of concentration correspond well to the areas with high coliform/enterococcus ratios, indicative of human inputs (Fig. 1).

 

Nitrogen and phosphorus concentrations in storm drain inputs show similar patterns to those indicated by bacterial ratios, alkalinity and caffeine.  Phosphorus averaged 2.5-times the concentration found in lake water and was most concentrated at the south and north ends of downtown, near the fish hatchery, at the tip of Reely Point, and at the extreme west end of Clear Lake (Fig. 2).  This pattern was repeated for nitrogen concentrations in storm drains as well as total suspended solids (an indicator of erosion).  N:P ratios in storm drain water were generally in the range seen for sewage, manure and other excretory products (Downing and McCauley 1992), but greatly below those that would result from drainage of agricultural fields.

 

Several of the storm drains show signatures that make them likely to supply substances like bacteria and nutrients derived from human activities.  These substances can enter storm drains due to line breaks yielding cross contamination through soil percolation, through overflows of sanitary systems or fields during rain storms, through saturation of relict septic systems within the city, through backups of sanitary systems by indirect connections (e.g., leakage of domestic sewage through sump systems), through accidental direct connection of sanitary drains to the storm drain system, or through other pathways.  All of the storm drains showed high fecal coliform concentrations, so other avenues, such as pet waste control and elimination of potential livestock inputs might also serve to decrease fecal coliform concentrations at routine lake monitoring stations.  Again, it should be stressed that these analyses concerned only City of Clear Lake storm drains, but all other storm drains around the lake are likely to show very similar signatures.

 

A third bacterial analysis was undertaken in 1998 to determine whether all parts of the lake had equal bacterial concentrations of bacteria, to use bacterial patterns to indicate probable sources, to examine sediments as a source or sink for bacteria and to examine depth profiles of bacteria.  A regular grid of sampling sites, five series of water-column profiles and 20 sediment grid samples were used to determine spatial patterns in fecal coliform bacteria, E. coli, enterococci, chloride and nutrients.  Maps were made to indicate spatial patterns and directions of concentration gradients.  Spatial trends in bacteria concentrations echo the results of storm drain analyses along city shores, but suggest several other potential bacteria sources outside of city limits.  Bacteria were most concentrated along the north shore of the lake, but also near the City of Ventura and in South Bay.  Bacterial ratios suggest that downtown Clear Lake, city lands west of Reely Point, the City of Ventura and developed property in South Bay and along the south shore of Clear Lake constitute potential sources of human input.  Depth profiles of bacteria and nutrients show that bacteria are mixed throughout the water column.  Sediment bacterial numbers are sometimes high, and are most concentrated near shore, near the cities of Clear Lake and Ventura, and in the center of the lake north of the Island.  Spatial patterns across the lake point to the same areas of the City indicated by storm drain analyses, but suggest several other areas of significant potential input.  These analyses were expanded in the Diagnostic / Feasibility Study in 1999 to examine the spatial pattern of bacteria at monthly intervals across the open-water season.

 

3.  Methods. 

 

a.  Sampling Design and Field Collections.  The perimeter of Clear Lake was measured to determine an appropriate spacing for sampling sites.  The shoreline length of Clear Lake is approximately 22 kilometers, and one hundred sampling sites around the perimeter were desired.  Thus, sampling sites were located approximately 220 meters apart, and samples were taken at a distance of 20 m from shore.  An arbitrary point on the western end of Clear Lake was chosen as the starting point, and two teams moved around the perimeter in opposite directions to complete the perimeter sampling.  Location of sampling points were determined and recorded using differentially-correcting GPS.  In addition to the perimeter sites, samples were taken from sites across the body of the lake. A grid with 500 m by 500 m blocks was overlain on the lake, and one sample was taken from each.  Fifty samples were taken from this grid, with sampling sites again being located and recorded using differential GPS.  All samples were taken at a depth of 0.25 meters below the lake surface.  All perimeter samples were taken on October 14, 1998, while the grid samples were taken on October 15, 1998.

 

Water profile and sediment samples were also taken on October 15, 1998.  Depth profiles of bacteria and nutrients were determined by sampling at the surface and one-meter depth intervals with a 5-liter Van Dorn bottle rinsed continuously with ambient lake water.  Nutrient samples were collected into chemically clean, opaque bottles and were transported cold to the laboratory for analysis.  Bacterial samples were collected into sterile bottles and refrigerated until analyzed.  Sediments were collected with a clean Ponar grab at 20 different sites and bacterial analyses were performed on elutriates and by the most probable number (MPN) method on solid sediment samples.

 

b.  Analytical methods.  We used standard protocols (APHA 1995, Hach Company 1992) to perform sample bottle and glassware preparation, sample preservation, and laboratory procedures.  Steps taken for quality assurance and quality control included taking replicate water samples in the field and analyzing triplicate samples in the laboratory.  Assays using these protocols included chloride, total nitrogen and total phosphorus.  Chemical analyses were performed as discussed above. Microbiological determinations of fecal coliform bacteria, E. coli and enterococci were conducted by UHL and followed the membrane filtration procedure with confirmation. 

 

c.  Mapping methods.  Surface concentration contour maps of the different constituents analyzed were created by interpolating the data collected at the different sampling sites by standard geostatistical techniques.  These maps were created using Surfer (Golden Software, Golden, Colorado).  The interpolation method used was a geostatistical procedure called kriging, which allows data trends to be accurately approximated.  This procedure assigned values to 10 m by 10 m blocks of the lake, which allowed fine details of trends to be estimated.  These lake surface maps were then overlain on topographic maps to allow visualization of the relationship between in-lake trends in concentrations and watershed characteristics. 

 

4.  Results.

 

a.  Microbial Analyses.  Fecal coliform concentrations varied significantly across the lake (Fig. 3) with low concentrations in open waters, and higher concentrations along the shore.  Very strong concentrations were found near the City of Ventura and plume-like concentration gradients occurred along the north shore from the extreme west of Clear Lake city limits to the southern side of downtown Clear Lake.  Other significant concentrations were found just west of the Clear Lake State Park near Lekwa Marsh, and northwest of the Park toward Grand View Point.  E. coli concentrations echoed the distribution of fecal coliforms with very similar levels of concentration (Fig. 3).  This suggests that much of the fecal coliform bacteria found in Clear Lake is E. coli.  Enterococci were most concentrated near Ventura, but also showed points of concentration along the north shore.  Along city shores, bacterial abundances are strongly correlated with the points of concentration seen in the storm drain effluents measured in September.

 

b.  Water Column Profiles of Bacteria and Nutrients.  Bacteria were distributed throughout the water column, probably because high wind and wave exposure can mix bacteria to the bottom of a lake the depth of Clear Lake.  The profiles echo the general west to east gradient in bacterial numbers seen in Figure 2.  Some of the highest fecal coliform and E. coli concentrations were found at 4 meters depth (13 feet).  The mixed nature of Clear Lake does not allow water column profiles to shed further light on the potential sources of bacteria.

 

c.  Sediment Bacteria Distributions.  Under certain conditions, enteric bacteria can survive and even reproduce in warm, nutrient rich sedimentary environments.  We therefore sampled twenty random sites to estimate the degree of coliform concentration in sediments.  Virtually all sediment elutriate samples showed very low concentrations of fecal coliforms, E. coli and enterococci, but direct test of sediments for fecal coliforms (using the “most probable number” method) showed very high, often extreme concentrations of fecal coliforms.  Nine out of the fourteen nearshore stations showed fecal coliform concentrations >100 colonies per 100 ml.  All of the stations showing >1000 colonies per 100 ml were in the eastern basin of Clear Lake, toward the City of Clear Lake.  The highest sediment concentration (>10,000 colonies per 100 ml) was found in the deepest part of the lake, off the island near Grand View Point.  The source of sediment fecal coliforms is not known but high concentrations near shore near areas such as downtown, the west end of the City of Clear Lake, and Ventura (areas showing high surface water fecal coliforms and/or high fecal coliform concentrations in storm drain effluent) suggest human origins, while the very high concentration found in the center of the lake could indicate avian or human origins. 

 

B.        Seasonal Variation in the Spatial Distribution of Enteric Bacteria.

 

Initial work in 1998 stimulated an analysis within the Diagnostic / Feasibility study of the seasonal variation of spatial distributions of bacteria.  Therefore, using similar methods to the spatial analyses discussed above, maps of fecal coliforms, E. coli, and fecal enterococci were created during May, June, July, August, September and October of 1999. 

 

1.  Fecal Coliforms.  The maps of bacteria in Fig. 4 indicate several important points.  First, the fact that concentrations are high near shore and low in the center of the lake indicates that bacteria originate on shores, moving into water.  It is unlikely, therefore, that aquatic animals such as water birds are a significant source of bacteria to Clear Lake.  Second, concentrations across the lake become quite elevated in mid-summer, especially after periods of protracted rainfall, such as July 1999.  Third, source areas along shores are quite consistent in where bacteria are concentrated, suggesting that there are source areas that could be localized for remediation.  Fourth, bacteria seem most concentrated in the Little Lake.  This is quite reasonable since much of the water load arises in the west and the periods of intense rainfall apparently bring in substantial watershed bacteria.  Finally, although some concentration is found in the west of the basin, much of the residential and commercial shoreline appears to be a bacteria source.  Therefore, remedial measures taken in the urban area of the shoreline could have a substantial impact on decreasing bacteria concentrations in Clear Lake.

 

2.  E. coli.  Patterns of spatial distribution of E. coli were similar to those seen for fecal coliforms (Fig. 5).  Concentrations were, however, substantially lower and rarely increased above the limits suggested by EPA for long-term average concentrations.  Even during mid-summer when some very high, very localized concentrations were observed, lake-wide concentration of E. coli were quite low.  One surprising result is that these bacteria can spread completely across the lake (e.g., August, Fig. 5).  This is counter-intuitive, since they are supposed to have a very short survival time in freshwater.  The warm temperatures and rich nutrient and organic matter environment is likely to prolong their survival and potentially those of other enteric bacteria.

 

3.  Fecal Enterococci.  Fecal enterococci are more abundant in the excrement of non-human animals so concentrations of it may indicate higher animal inputs.  Fecal enterococci distributions are generally similar to those seen for E. coli, except that strong concentrations are seen around North Beach and in the Little Lake (Fig. 6).  Some of the fecal bacteria especially in the west end may therefore be of animal origin.  Again, these organisms spread out to fairly uniform distributions across the lake in August and September when temperatures are fairly warm and organic matter abundant.

 

4.  General Comments on Spatial Analyses of Bacteria.  Although the aggregate from these maps (Fig. 7) suggests that much of the shoreline is a source of bacteria to the lake, darkest areas are quite consistent in their placement.  This suggests that remediation might be achieved by seeking out and pinpointing the sources of bacteria and correcting a series of localized problems.  It is important to note that E. coli concentrations are very localized within the lake and that few very high levels were observed throughout the study.  The water is generally quite safe from a bacteriological point of view, but most caution should be exercised at specific high-risk areas during very warm weather.

 

C.        Beach Analyses.

 

During 2000, the IDNR monitored fecal bacteria weekly at the two state beaches on Clear Lake.  Fecal coliforms only exceeded the suggested 200 CFU/100 ml limit at one of the beaches (McIntosh Woods) on one occasion.  E. coli was only monitored for five weeks, but never exceeded the EPA suggested limit at either beach, while fecal enterococcal abundance exceeded the limit (26 CFU/100 ml) three times out of 18 weeks at State Park Beach, and six times out of 18 weeks at McIntosh Woods Beach.  State monitoring indicated that bacteria concentrations were routinely higher at McIntosh Woods than at State Park Beach.  The reason for this is clear from Figs. 4-6.

 

 

References:

 

APHA (American Public Health Association). 1995. Standard Methods for the Examination of Water and Wastewater. 19th edition. American Public Health Association, Washington, DC.

 

Bernardot, D. 1996. Caffeine and gymnastic performance. USA Gymnastics Magazine Online (www.usa-gymnastics.org/publications/1996/4/body-balance.html)

 

Burkow, R. (ed.) 1977. The Merck Manual of Diagnosis and Therapy, 13th Edition.  Merck Sharp & Dohme Research Laboratories.  Rahway, NJ.

 

Crumpton, W. G., T. M. Isenhart, and P. D. Mitchell. 1992. Nitrate and organic nitrogen analyses using second derivative spectroscopy. Limnology and Oceanography 37: 907-913.

 

Downing, J.A. and E. McCauley. 1992. The nitrogen:phosphorus relationship in lakes.  Limmnology and Oceanography  37: 936-945.

 

Hach Company. 1992. Water Analysis Handbook. Second edition. Hach Company, Loveland, Colorado.

 

Meade, R.H. (ed.) 1995.  Contaminants in the Mississippi River, 1987-92.  U.S. Geological Survey Circular 113.

 

 


TABLE 1.  Analytical results from tests of water collected from thirty storm drain sites in the City of Clear Lake, Iowa on September 23, 1998.  Data highlighted in red indicate high values indicating human and/or animal input.

 

Site

Location

Fecal Coliforms (colonies/ 100 mL)

E. coli (colonies/ 100 mL)

Enterococci (colonies/ 100 mL)

FC/ent

Ec/ent

Total Nitrogen (TN; mg/L)

Total Phosphorus (TP; mg/L)

TN:TP

Alkalinity mg/L

Conduct-ivity (mmho/ cm)

pH

Caffeine (ng/L)

Chloride (mg/L)

Total Suspended Solids (g/L)

1

2700 block, S. Lakeview Drive

5726

3630

32474

0.18

0.11

1.75

316

5.6

0

68

2.6

120

4.2

0.02468

2

2200 block, S. Lakeview Drive

3659

4185

21646

0.17

0.19

1.27

277

4.6

0

50

2.3

76

1.4

0.04209

3

7th Ave. S., south side of public approach

2736

2924

16074

0.17

0.18

2.20

480

4.6

37

104

6.8

780

3.6

0.02970

4

7th Ave. S., north side of public approach

3903

5487

11846

0.33

0.46

2.37

628

3.8

35

99

6.8

220

8.3

0.20188

5

6th Ave. S., south side of public approach

4127

4878

8640

0.48

0.56

3.88

696

5.6

28

92

6.8

85

8.9

0.12054

6

6th Ave. S., north side of public approach

4199

5624

4967

0.85

1.13

2.06

571

3.6

23

58

7.5

100

3.8

0.09750

7

4th Ave. S. and S. Lakeview Drive

6902

6874

6680

1.03

1.03

1.28

291

4.4

0

56

3.7

240

2.8

0.05877

8

1st Ave. S. and S. Lakeview Drive, south side

8290

10144

7441

1.11

1.36

2.51

326

7.7

21

63

7.1

550

9.5

0.09489

9

1st Ave. S. and S. Lakeview Drive, north side

5578

5407

8712

0.64

0.62

1.61

420

3.8

34

57

8.2

240

8.3

0.06744

10

Main St. Boat Ramp

5785

4707

6010

0.96

0.78

1.09

72

15.2

0

53

3.8

430

8.7

0.01078

11

1st Ave. N. and N. Lakeview Dr., south side

5650

4852

7341

0.77

0.66

1.17

228

5.1

0

44

3.2

190

8.7

0.03278

12

1st Ave. N. and N. Lakeview Dr., north side

5346

4039

5092

1.05

0.79

1.21

250

4.8

0

38

3.5

99

1.8

0.03086

13

2nd Ave. N. and N. Lakeview Dr.

6569

2884

3317

1.98

0.87

0.86

396

2.2

0

35

3.4

86

1.4

0.01044

14

4th Ave. N. and N. Lakeview Dr.

9063

3330

4123

2.20

0.81

1.48

413

3.6

0

57

3.2

84

3.3

0.07766

Site

Location

Fecal Coliforms (colonies/ 100 mL)

E. coli (colonies/ 100 mL)

Enterococci (colonies/ 100 mL)

FC/ent

Ec/ent

Total Nitrogen (TN; mg/L)

Total Phosphorus (TP; mg/L)

TN:TP

Alkalinity mg/L

Conductivity (mmho/cm)

pH

Caffeine (ng/L)

Chloride (mg/L)

Total Suspended Solids (g/L)

15

1101 N. Shore Drive

10411

4302

19774

0.53

0.22

1.94

809

2.4

29

84

7.6

24

10.2

0.07308

16

IDNR Fish Hatchery

14065

4174

15754

0.89

0.26

1.49

359

4.2

0

54

3.0

100

2.6

0.04078

17

1615 N. Shore Drive

13775

4304

19234

0.72

0.22

1.17

160

7.3

0

37

2.6

37

1.0

0.01758

18

18th St. W. Public Approach

13357

6714

18301

0.73

0.37

1.14

273

4.2

0

38

2.6

40

3.7

0.01216

19

2100 block N. Shore Drive

10122

6504

20769

0.49

0.31

2.82

409

6.9

82.5

335

7.5

440

15.1

0.10245

20

2300 block N. Shore Drive

7511

7813

20769

0.36

0.38

1.15

276

4.2

0

63

3.4

58

3.2

0.03592

21

West 2401 N. Shore Drive

7747

8640

26370

0.29

0.33

1.18

195

6.1

0

32

2.2

57

1.4

0.01113

22

2510 North Shore Drive

7910

9106

14877

0.53

0.61

1.22

175

7.0

0

44

2.2

67

1.7

0.01053

23

North Shore Drive and Orchard Lane

8271

9521

16732

0.49

0.57

0.90

135

6.7

0

32

2.3

37

2.1

0.01117

24

2700 block N. Shore Drive

10012

10776

15524

0.64

0.69

1.91

241

7.9

26

74

7.3

83

2.8

0.03365

25

2906 N. Shore Drive

15090

11599

14057

1.07

0.83

1.33

252

5.3

30

77

7.7

130

2.4

0.03137

26

3308 N. Shore Drive

15499

12985

12842

1.21

1.01

1.88

317

5.9

24

61

6.7

190

1.2

0.01953

27

3805 N. Shore Drive

21791

17281

18059

1.21

0.96

1.01

186

5.4

0

32

3.9

190

0.7

0.20974

28

34th St. W

27146

20701

19536

1.39

1.06

2.17

863

2.5

21

60

6.9

380

2.9

0.05205

29

N. Shore Drive and N. 9th St. SW

36860

22334

12094

3.05

1.85

0.65

101

6.5

0

34

2.3

30

1.7

0.00520

30

33rd St. W

38468

26742

20787

1.85

1.29

1.96

675

2.9

34

75

8.1

37

9.4

0.06977

 

 

 

 


FIGURE 1.  Color-coded bacterial concentrations in storm drains around the City of Clear Lake.  Note that storm drain analyses were funded directly by the City of Clear Lake so dozens of storm drains from other residential and commercial areas were not tested but would likely yield similar values.

 


FIGURE 2.  Color-coded chemical concentrations in storm drains around the City of Clear Lake.  Note that storm drain analyses were funded directly by the City of Clear Lake so dozens of storm drains from other residential and commercial areas were not tested but would likely yield similar values.

 

 


FIGURE 3.  Spatial patterns of bacterial concentrations in Clear Lake, Iowa.  These analyses were funded directly by the City of Clear Lake.

 

FIGURE 4.  Spatial patterns of fecal coliform concentrations in Clear Lake, Iowa across the open water season of 1999.  The arrows point up-gradient in bacteria concentration so point toward the likely source of the bacteria.  The larger and darker arrows indicate a steeper gradient.

 


FIGURE 5.  Spatial patterns of E. coli bacteria concentrations in Clear Lake, Iowa across the open water season of 1999.  The arrows point up-gradient in bacteria concentration so point toward the likely source of the bacteria.  The larger and darker arrows indicate a steeper gradient.

 


FIGURE 6.  Spatial patterns of fecal enterococcal bacteria concentrations in Clear Lake, Iowa across the open water season of 1999.  The arrows point up-gradient in bacteria concentration so point toward the likely source of the bacteria.  The larger and darker arrows indicate a steeper gradient.

 


FIGURE 7.  Aggregate patterns of fecal coliforms across the season.  Red lines are drawn along shore in areas where the vectors in Figure 4 indicate shore origin of fecal coliforms.  A new stripe was drawn for every month when the shore appeared to be a source.  Six stripes offshore indicate that the shore is a likely source in all of May-October.