LIST OF FIGURES

 

 

CHAPTER 1

 

Figure   1.    Location of Clear Lake within Cerro Gordo and Hancock counties and the state of Iowa.

 

FIGURE   2.    Location of Clear Lake within Cerro Gordo and Hancock counties.

 

FIGURE   3.    Map of Clear Lake watershed representing prairie and forest derived soils.

 

FIGURE   4.    Distribution of common soil series in the Clear Lake watershed.

 

FIGURE   5.    Distribution and percentage of soil hydrogroups in the Clear Lake watershed.

 

CHAPTER 2

 

FIGURE   1.    Clear Lake activities.

 

FIGURE   2.    Importance points.

 

FIGURE   3.    Projects: visitors.

 

FIGURE   4.    Projects: local residents.

 

FIGURE   5.    Land use changes: visitors.

 

FIGURE   6.    Land use changes: local residents.

 

FIGURE   7.    Willingness to pay for Plan A: visitors.

 

FIGURE   8.    Willingness to pay for Plan A: local residents.

 

FIGURE   9.    Willingness to pay for Plan B, low improvement: visitors.

 

FIGURE  10.   Willingness to pay for Plan B, low improvement: local residents.

 

FIGURE  11.   Willingness to pay for Plan B, high improvement: visitors.

 

FIGURE  12.   Number of trips taken at varying quality levels.

 
CHAPTER 5
 
FIGURE   1.    Trend in total phosphorus and Secchi disk transparency since the early 1970s.

 

FIGURE   2.    Open water sampling points in Clear Lake, Iowa.

 

FIGURE   3.    Trends in water temperature in Clear Lake, Iowa during 1998-2000.

 

FIGURE   4.    Trends in water clarity in Clear Lake, Iowa during 1998-2000.

 

FIGURE   5.    Trends in oxygen concentrations in Clear Lake, Iowa during 1998-2000.

 

FIGURE   6.    Trends in alkalinity concentrations in Clear Lake, Iowa during 1998-2000.

 

FIGURE   7.    Trends in pH of Clear Lake, Iowa during 1998-2000.

 

FIGURE   8.    Trends in total dissolved solids (TDS) in Clear Lake, Iowa during 1998-2000.

 

FIGURE   9.    Trends in silica in Clear Lake, Iowa during 1998-2000.

 

FIGURE  10.   Trends in whole-lake, volume weighted concentrations of silica in Clear Lake, Iowa during 1998-2000.

 

FIGURE  11.   Comparison of total suspended solids concentrations in Clear Lake with those found in the 2000 Iowa Lake Water Quality Survey (Downing & Ramstack 2001).

 

FIGURE  12.   Trends in total suspended solids (TSS) in Clear Lake, Iowa during 1998-2000.

 

FIGURE  13.   Volume weighted trends in suspended solids in Clear Lake, Iowa during 1998-2000.

 

FIGURE  14.   Trends in inorganic suspended solids (ISS) in Clear Lake, Iowa during 1998-2000.

 

FIGURE  15.   Trends in volatile suspended solids (VSS) in Clear Lake, Iowa during 1998-2000.

 

FIGURE  16.   Comparison of total phosphorus concentrations in Clear Lake with those found in the 2000 Iowa Lake Water Quality Survey (Downing & Ramstack 2001).

 

FIGURE  17.   Comparison of total phosphorus and total nitrogen concentrations in Clear Lake with those found in the 1990 (Bachmann et al 1992) and 2000 Iowa Lake Water Quality Surveys (Downing & Ramstack 2001), as well as world lake data (Downing and McCauley 1993).

 

FIGURE  18.   Trends in total nitrogen in Clear Lake, Iowa during 1998-2000.

 

FIGURE  19.   Trends in nitrate in Clear Lake, Iowa during 1998-2000.

 

FIGURE  20.   Trends in ammonia nitrogen in Clear Lake, Iowa during 1998-2000.

FIGURE  21.   Trends in volume weighted concentrations of various forms of nitrogen in Clear  Lake, Iowa during 1998-2000.

 

FIGURE  22.   Trends in total phosphorus concentrations in Clear Lake, Iowa during 1998-2000.

 

FIGURE  23.   Trend in volume weighted concentrations of total phosphorus in Clear Lake, Iowa during 1998-2000.

 

FIGURE  24.   Trend in the volume weighted ratio of total nitrogen to total phosphorus  concentration in Clear Lake, Iowa during 1998-2000.

 

FIGURE  25.   Trends in the volume weighted chlorophyll a concentrations in Clear Lake, Iowa during 1998-2000.

 

FIGURE  26.   Trends in percentage taxonomic composition of phytoplankton in Clear Lake, Iowa during 1998-2000 (by biomass). 

 

FIGURE  27.   Photograph of Bacillariophycaea (Melosira sp.) from Clear Lake.

 

FIGURE  28.   Photograph of Bacillariophycaea (Asterionella sp.) from Clear Lake.

 

FIGURE  29.   Photograph of Cyanobacteria (Spirulina sp.) from Clear Lake.

 

FIGURE  30.   Photograph of Cyanobacteria (Oscillatoria sp.) from Clear Lake.

 

FIGURE  31.   Photographs of Cyanobacteria (Anabaena sp.) from Clear Lake.

 

FIGURE  32.   World trend in Cyanobacteria abundance as related to the total phosphorus concentrations in lakes.

 

FIGURE  33.   Secchi disk measurements and macrophyte abundance in Clear Lake from 1896 to 2000.

 

FIGURE  34.   Clear Lake bathymetric map, 2000.

 

FIGURE  35.   Clear Lake bathymetric map, 1935.

 

FIGURE  36.   Clear Lake bathymetric map, original post-glaciation estimate.

 

FIGURE  37.   Clear Lake sediment deposition map, 1935-2000.

 

FIGURE  38.   Clear Lake sediment deposition map, original lake basin estimate-2000.

 

FIGURE  39.   Little Lake section of Clear Lake sediment deposition map, original lake basin estimate-2000.

 

FIGURE  40.   Changes in ambient total phosphorus concentration in Clear Lake predicted from the Canfield/Bachmann model for various levels of reduction in phosphorus input from the watershed.

 

FIGURE  41.   Changes in ambient water clarity in Clear Lake predicted form the Canfield/Bachmann model for various levels of reduction in phosphorus input from the watershed.

 
CHAPTER 6

 

FIGURE   1.    Color-coded bacterial concentrations in storm drains around the City of Clear Lake. 

 

FIGURE   2.    Color-coded chemical concentrations in storm drains around the City of Clear Lake. 

 

FIGURE   3.    Spatial patterns of bacterial concentrations in Clear Lake, Iowa. 

 

FIGURE   4.    Spatial patterns of fecal coliform concentrations in Clear Lake, Iowa across the open water season of 1999. 

 

FIGURE   5.    Spatial patterns of E. coli bacteria concentrations in Clear Lake, Iowa across the open water season of 1999. 

 

FIGURE   6.    Spatial patterns of fecal enterococcal bacteria concentrations in Clear Lake, Iowa across the open water season of 1999. 

 

FIGURE   7.    Aggregate patterns of fecal coliforms across the season.

 

CHAPTER 7

 

FIGURE   1.    Locations of the sonde (·), Clear Lake Municipal Water Treatment Facility (·), and 3700 points used for calculation of physical wave characteristics (·).

 

FIGURE   2.    Turbidity (NTU) (·), chlorophyll a concentrations (mg·L-1) (·), and wind speed (m·s-1) (·) observed at Clear Lake between July 25, 2000 and October 19, 2000. 

 

FIGURE   3.    Peaks and troughs in spectral trends in Turbidity (NTU) (¾) and wind speed (m·s-1) (¾), both averaged over one hour intervals, are similar, implying a role of wind–induced turbulence in sediment resuspension at Clear Lake.

 

FIGURE   4.    Wave velocities (cm·s-1) at the lake bottom during a 5m·s-1 wind event along the prevailing Northwest-Southeast (330°-170°) wind axis.

 

FIGURE   5.    Wave velocities (cm·s-1) at the lake bottom during a 10m·s-1 wind event along the prevailing Northwest-Southeast (330°-170°) wind axis.

 

FIGURE   6.    Wave velocities (cm·s-1) at the lake bottom during a 15m·s-1 wind event along the prevailing Northwest-Southeast (330°-170°) wind axis.

 

FIGURE   7.    Wave velocities (cm·s-1) at the lake bottom during a 20m·s-1 wind event along the prevailing Northwest-Southeast (330°-170°) wind axis.

 

FIGURE   8.    Wave velocities (cm·s-1) at the lake bottom during a 25m·s-1 wind event along the prevailing Northwest-Southeast (330°-170°) wind axis.

 

FIGURE   9.    Wave velocities (cm·s-1) at the lake bottom during 10 m·s-1 and 15 m·s-1 wind events along a North-South (0°-180°) wind axis.

 

FIGURE  10.   Wave velocities (cm·s-1) at the lake bottom during 10 m·s-1 and 15 m·s-1 wind events along an East-West (270°-90°) wind axis.

 

FIGURE  11.   Wave velocities (cm·s-1) at the lake bottom during 10 m·s-1 and 15 m·s-1 wind events along a Northeast-Southwest (225°-45°) wind axis.

 

FIGURE  12.   Flux of (a.) turbidity (NTU) (¾), (b.) ammonium (mg·L-1) (¾), and (c.) total phosphorus (mg·L-1) (¾) during a significant wind event (10m·s-1) (¾) on September 27, 2000. 

 

FIGURE  13.   Violations of the No Wake Zone on Clear Lake, Iowa

 

FIGURE  14.   Trends in the mean number of boats passing the sonde per 10 minute interval (¾), turbidity (NTU) (¾), and wind speed (10m·s-1) (¾) between August 25, 2000 and September 3, 2000.

 

CHAPTER 8

 

FIGURE   1.    Private well log downloaded from the IGSB’s Virtual GEOSAM database.

 

FIGURE   2.    Hydraulic heads in major aquifers in relation to Clear Lake stage.

 

FIGURE   3.    Map of Clear Lake watershed showing location of seepage meter measurements in 1999 and 2000.  North is to the top of the map.  Sections are 1 mi (1.6 km) square.

 

FIGURE   4.    Boxplots showing seepage measurements at the 21 sites (see Figure 3).

 

FIGURE   5.    Cross-sectional diagram showing piezometers in a nested configuration.

 

FIGURE   6.    Topographic map showing location of piezometer nests (blue dots) and boundaries of cross-sections (lines) for discharge calculations by Darcy’s Law.

 

FIGURE   7.    Simulation of groundwater flow in the vicinity of Clear Lake using the AE model GFLOW2000. 

 

FIGURE   8.    Calibration curve for the AE simulation shown in Figure 7. 

 

FIGURE   9.    Boxplots showing Total P concentrations in groundwater.

 

FIGURE  10.   Boxplots showing concentrations of Total P at each piezometer.  Differences in concentrations exist between piezometers.

 

FIGURE  11.   Vertical profile of Total P concentration in groundwater at all sites.  Highest values occur at shallow depths, but there is no consistent trend with depth.

 

FIGURE  12.   Variation of Soil P (Olsen method) with depth in core. 

 

FIGURE  13.   Total N concentrations in groundwater.

 

FIGURE  14.   SiO2 concentrations in groundwater. 

 

FIGURE  15.   SiO2 concentrations in groundwater among the piezometers. 

 

FIGURE  16.   Relationship of Na and Cl concentrations (meq/L) in groundwater. 

 

FIGURE  17.   Profile of 3H (TU) in groundwater in the piezometers. 

 

CHAPTER 9

 

FIGURE   1.    Map of Clear Lake watershed showing land use and the location of Ventura Marsh and the reference system (Little Lake).

 

FIGURE   2.    Map of Ventura Marsh showing the water quality, plankton, and benthic sampling sites

 

FIGURE   3.    Inorganic suspended solids and Secchi disc transparency for Ventura Marsh from April 14, 1999 to September 27, 2000.

 

FIGURE   4.    The relationship between total phosphorus and phytoplankton biomass was examined. Figure 4A is of the turbid phase (4/12/99 –6/6/00) and Figure 4B is of the clear water phase (6/7/00 – 9/27/00).

 

FIGURE   5.    The relationship between Inorganic suspended solids and Secchi disk transparency was examined.

 

FIGURE   6.    Phytoplankton biomass and percent composition for Ventura Marsh from May 13, 1999 to September 27, 2000.

 

FIGURE   7.    Zooplankton biomass and percent composition for Ventura Marsh from April 12, 1999 to September 27, 2000.

 

FIGURE   8.    Box-whisker plot of cladoceran and copepod lengths during premanipulation (4/12/99 – 8/16/99), postmanipulation 1 (8/17/99 – 10/15/99), postmanipulation 2 (3/14/99 – 6/6/00), and postmanipulation 3 (6/7/00 – 9/27/00). 

 

FIGURE   9.    Grazing rate and phytoplankton biomass for Ventura Marsh from May 13, 1999 to September 27, 2000.

 

FIGURE  10.   Benthic biomass and percent composition for Ventura Marsh from April 12, 1999 to September 27, 2000.

 

FIGURE  11.   Box-whisker plot of chironomid and oligochaete lengths during premanipulation (4/12/99 – 8/16/99), postmanipulation 1 (8/17/99 – 10/15/99), postmanipulation 2 (3/14/99 – 6/6/00), and postmanipulation 3 (6/7/00 – 9/27/00).

 
CHAPTER 10

 

FIGURE   1.    Sampling sites and sub-basins used for modeling purposes in the Clear Lake watershed.

 

FIGURE   2.    Watershed areas differentiated for nutrient flux calculations in the Clear Lake watershed.

 

FIGURE   3.    1998-1999 Total Phosphorus load (kg).

 

FIGURE   4.    1999-2000 Total Phosphorus load (kg).

 

FIGURE   5.    Average Total Phosphorus load (kg).

 

FIGURE   6.    Land uses in the Clear Lake watershed.

 

FIGURE   7.    Present conditions modeling results from AGNPS model for the Clear Lake watershed.

 
CHAPTER 11

 

FIGURE   1.    Soil samples taken in Clear Lake watershed summer of  1999.

 

FIGURE   2.    Cropping and tillage systems in the Clear Lake watershed.

 

FIGURE   3.    Soil survey of the Clear Lake watershed.

 

FIGURE   4.    Olsen-P in sub-sections of the Clear Lake watershed.

 

FIGURE   5.    Bray-1 P in sub-sections of the Clear Lake watershed.

 

FIGURE   6.    Mehlich-3 P in sub-sections of the Clear Lake watershed.

 

FIGURE   7.    Iron-oxide strip P in sub-sections of the Clear Lake watershed.

 

FIGURE   8.    Water extractable P in sub-sections of the Clear Lake watershed.

 

FIGURE   9.    Soil pH in sub-sections of the Clear Lake watershed.

 

CHAPTER 14

 

FIGURE   1.    Present conditions modeling results from AGNPS model for the Clear Lake watershed.

 

FIGURE   2.    Top 1%, 5%, and 10% of phosphorus exporting cropland cells determined by AGNPS model.

 

FIGURE   3.    Proposed wetland restoration and construction in the Clear Lake watershed.

 

FIGURE   4.    Schematic diagram of nutrient retention wetlands and their nutrient retention rates.

 

FIGURE   5.    Aerial view of Ventura Marsh at the present time, and a visual representation of it in the future.

 

FIGURE   6.    Aerial view of Ventura Grade at the present time, and a visual representation of it in the future.

 

FIGURE   7.    Wind rose for Clear Lake.

 

FIGURE   8.    Proposed area of dredging and dredging depths in the Little Lake.

 

FIGURE   9.    Containment site for dredge spoil.

 

FIGURE  10.   Bathymetric map of the Clear Lake after dredging.

 

FIGURE  11.   Post restoration water quality monitoring sites.