| Report Year: 2009 |
| Mitchell Lake, Black Hawk County |
| Summary Data Table |
| Parameter | 6/24/2009 | 7/29/2009 | 2009 | 2007 | 2006 | 2005 | 2004 | 2003 | 2002 | 2001 | 2000 |
| Lake Depth (m) | 16.8 | 17.0 | 16.9 | - | - | 15.1 | 14.8 | 14.0 | 11.9 | 12.3 | 10.4 |
| Thermocline Depth (m) | 1.3 | 4.5 | N/A | N/A | N/A | N/A | N/A | N/A | N/A | N/A | N/A |
| Secchi Disk Depth (m) | 1.6 | 1.3 | 1.5 | - | - | 1.0 | 0.8 | 0.8 | 0.8 | 1.5 | 1.1 |
| Temperature(oC) | 26.0 | 22.8 | 24.4 | - | - | 25.7 | 24.3 | 23.1 | 24.6 | 23.3 | 24.2 |
| Dissolved Oxygen (mg/L) | 8.5 | 6.9 | 7.7 | - | - | 9.8 | 10.8 | 11.3 | 7.7 | 5.4 | 7.4 |
| Dissolved Oxygen Saturation (%) | 105 | 80 | 92.5 | - | - | 120.3 | 131.0 | 133.3 | 92.8 | 67.2 | 87.9 |
| Specific Conductivity (μS/cm) | 400.0 | 400.0 | 400.0 | - | - | 426.6 | 436.7 | 597.5 | 646.4 | 559.8 | 554.3 |
| Turbidity (NTU) | 1.7 | 1.2 | 1.4 | - | - | 11.7 | 17.5 | 10.6 | 7.5 | 10.7 | 31.3 |
| Chlorophyll a (μg/L) | 10.0 | 12.0 | 11.0 | - | - | 47.5 | 46.5 | 25.9 | 19.7 | 12.1 | 4.2 |
| Total Phosphorus as P (μg/L) | 39 | 43 | 41 | - | - | 41 | 103 | 49 | 49 | 49 | 86 |
| SRP as P (μg/L) | - | - | - | - | - | 1 | 1 | 1 | 1 | - | - |
| Total Nitrogen as N (mg/L) | 0.93 | 0.87 | 0.90 | - | - | 0.95 | 1.57 | 1.31 | 1.08 | 1.26 | 0.90 |
| (Phenate)Ammonia Nitrogen (NH3 + NH4+) as N (μg/L) | 71 | 16 | 42 | - | - | 74 | 153 | - | - | - | - |
| (Phenate)Ammonia Nitrogen (NH3) as N (un-ionized)(μg/L) | 11.5 | 2.1 | 6.8 | - | - | 5.2 | 22.8 | - | - | - | - |
| Nitrate + Nitrite (NO3 + NO2) as N (mg/L) | 0.26 | - | 0.26 | - | - | 0.29 | 0.37 | 0.12 | 0.25 | 0.23 | 0.16 |
| TN:TP ratio | 24 | 20 | 22 | - | - | 25 | 16 | 31 | 22 | 31 | 12 |
| pH | 8.5 | 8.6 | 8.6 | - | - | 8.3 | 9.0 | 8.3 | 8.3 | 8.0 | 7.2 |
| Alkalinity as CaCO3 (mg/L) | 151 | 139 | 145 | - | - | 136 | 107 | 120 | 153 | 192 | 174 |
| Silica as Si (mg/L) | - | - | - | - | - | 2.08 | 4.31 | 4.39 | 1.62 | - | - |
| Dissolved Organic Carbon (mg/L) | 3.79 | 4.36 | 4.08 | - | - | 5.46 | 6.23 | 7.79 | 7.18 | - | - |
| Inorganic Suspended Solids (mg/L) | 3 | 2 | 2 | - | - | 5 | 5 | 5 | 4 | 4 | 3 |
| Volatile Suspended Solids (mg/L) | 3 | 5 | 4 | - | - | 8 | 7 | 7 | 6 | 3 | 3 |
| Total Suspended Solids (mg/L) | 6 | 6 | 6 | - | - | 11 | 12 | 12 | 10 | 7 | 7 |
| Carlson Trophic State Index (Secchi)* | 53 | 56 | 55 | - | - | 61 | 63 | 64 | 64 | 55 | 58 |
| Carlson Trophic State Index (Chl a)* | 53 | 55 | 54 | - | - | 68 | 68 | 63 | 60 | 55 | 45 |
| Carlson Trophic State Index (TP)* | 57 | 59 | 58 | - | - | 58 | 71 | 60 | 60 | 60 | 68 |
| *Index values generally range between 0 and 100, with increasing values indicating more eutrophic conditions. |