| Report Year: 2009 |
| North Twin Lake, Calhoun County |
| Summary Data Table |
| Parameter | 7/28/2009 | 6/4/2009 | 2009 | 2007 | 2006 | 2005 | 2004 | 2003 | 2002 | 2001 | 2000 |
| Lake Depth (m) | 3.1 | 3.0 | 3.1 | 3.3 | 3.2 | 3.4 | 3.7 | 3.5 | 3.4 | 3.8 | 3.3 |
| Thermocline Depth (m) | NIL | Nil | N/A | N/A | N/A | N/A | N/A | N/A | N/A | N/A | N/A |
| Secchi Disk Depth (m) | 0.6 | 0.7 | 0.6 | 0.7 | 0.6 | 1.5 | 1.0 | 2.4 | 1.6 | 0.7 | 0.4 |
| Temperature(oC) | 24.7 | 20.2 | 22.5 | 23.9 | 25.4 | 24.7 | 23.1 | 22.5 | 25.2 | 23.9 | 25.2 |
| Dissolved Oxygen (mg/L) | 8.8 | 9.5 | 9.1 | 8.4 | 11.8 | 8.3 | 8.1 | 10.1 | 9.0 | 9.2 | 9.0 |
| Dissolved Oxygen Saturation (%) | 106 | 105 | 105.4 | 99.0 | 142.8 | 99.1 | 94.1 | 115.2 | 109.2 | 106.7 | 108.2 |
| Specific Conductivity (μS/cm) | 450.0 | 450.0 | 450.0 | 520.5 | 494.8 | 496.6 | 499.0 | 517.4 | 604.5 | 542.2 | 463.7 |
| Turbidity (NTU) | 21.7 | 12.1 | 16.9 | 22.2 | 23.5 | 176.0 | 43.0 | 13.7 | 22.0 | 23.1 | 27.7 |
| Chlorophyll a (μg/L) | 40.0 | 13.0 | 26.5 | 40.4 | 41.3 | 47.0 | 30.1 | 11.5 | 28.2 | 102.4 | 101.9 |
| Total Phosphorus as P (μg/L) | 82 | 57 | 69 | 50 | 68 | 51 | 67 | 69 | 61 | 169 | 199 |
| SRP as P (μg/L) | - | - | - | 1 | - | 1 | 2 | 5 | 1 | - | - |
| Total Nitrogen as N (mg/L) | 1.73 | 0.28 | 0.92 | 2.04 | 1.83 | 1.80 | 1.50 | 1.75 | 1.47 | 3.38 | 2.23 |
| (Phenate)Ammonia Nitrogen (NH3 + NH4+) as N (μg/L) | 16 | 50 | 27 | 125 | 16 | 188 | 119 | - | - | - | - |
| (Phenate)Ammonia Nitrogen (NH3) as N (un-ionized)(μg/L) | 0.5 | 12.1 | 6.3 | 12.7 | 1.8 | 16.3 | 14.3 | - | - | - | - |
| Nitrate + Nitrite (NO3 + NO2) as N (mg/L) | 0.12 | 0.24 | 0.14 | 0.82 | 0.29 | 0.45 | 0.24 | 0.65 | 0.40 | 0.49 | 0.16 |
| TN:TP ratio | 21 | 2 | 12 | 48 | 27 | 38 | 22 | 30 | 31 | 26 | 11 |
| pH | 8.6 | 8.9 | 8.8 | 8.4 | 8.5 | 8.3 | 8.5 | 8.5 | 8.3 | 8.4 | 8.2 |
| Alkalinity as CaCO3 (mg/L) | 148 | 160 | 154 | 172 | 159 | 161 | 157 | 122 | 174 | 134 | 167 |
| Silica as Si (mg/L) | - | - | - | - | - | 12.11 | 4.26 | 8.43 | 10.12 | - | - |
| Dissolved Organic Carbon (mg/L) | 6.70 | 13.71 | 10.21 | 19.52 | 8.43 | 10.36 | 7.69 | 12.27 | 13.02 | - | - |
| Inorganic Suspended Solids (mg/L) | 5 | 7 | 6 | 7 | 12 | 7 | 7 | 5 | 5 | 7 | 34 |
| Volatile Suspended Solids (mg/L) | 23 | 12 | 18 | 8 | 17 | 7 | 6 | 7 | 10 | 12 | 11 |
| Total Suspended Solids (mg/L) | 28 | 20 | 24 | 14 | 29 | 11 | 14 | 12 | 15 | 19 | 45 |
| Carlson Trophic State Index (Secchi)* | 68 | 65 | 66 | 65 | 67 | 54 | 61 | 48 | 53 | 65 | 74 |
| Carlson Trophic State Index (Chl a)* | 67 | 56 | 63 | 67 | 67 | 68 | 64 | 55 | 63 | 76 | 76 |
| Carlson Trophic State Index (TP)* | 68 | 63 | 65 | 60 | 65 | 61 | 65 | 65 | 63 | 78 | 80 |
| *Index values generally range between 0 and 100, with increasing values indicating more eutrophic conditions. |