Governor Bond Lake TMDL
Final Report 5 September 2002
need another source. With abundant nitrogen availability, any addition of the limiting nutrient (e.g., TP)
results in rapid growth.
2.1.3 Trophic Status: Fertility Status
Trophic status often is used to describe the nutrient enrichment status of a lake ecosystem. Higher trophic
status is equated with more nutrient availability and higher productivity. Generally, mesotrophic to
eutrophic lakes are considered to be the best for supporting a variety of uses including fishing, aquatic life
support, swimming, boating, and others. Excessive nutrient load to lakes can result in nuisance algal
blooms and excessive turbidity. Very low nutrient status also can limit support of aquatic life by lack of a
sufficient nutrient supply.
Carlson Trophic State Indexes (TSIs) use measured parameters as indicators of trophic status. These TSIs
are based on TP concentration (TSI-TP), Chlorophyll-a concentration (TSI-Chla), or Secchi depth (TSI-SD).
The individual indices are often averaged for an overall TSI. However, in general, TSI-TP is
considered the best indicator of potential trophic status. The following diagram depicts the relationship
between TSI, trophic status, and nutrient status according to IEPA guidelines.
Figure 2-1 Trophic State Index Relationship to Lake Fertility
Governor Bond Lake is considered to be eutrophic to hypereutrophic (fertile to highly fertile); Trophic
State Indexes (TSI) are > 50 < 70 for eutrophic lakes and > 70 for hypereutrophic lakes. The 1998 Illinois
305(b) Report mean TSI-SD = 75.2, TSI-TP = 73.8, and TSI-Chla = 59.6, with the average TSI = 69.6. In
1999, these values were similar with TSI values as follows: TSI-SD = 73.7, TSI-TP = 67.6, and TSI-Chla
= 72.4, with and overall TSI of 71.2.
Governor Bond Lake is a constructed reservoir on the Kingsbury Branch within the Shoal Creek
Watershed HUC (07140203). As a Public Water Supply system, outflow is controlled by a rectangular
dam (40 ft high and 1,200 ft long) with a gravity driven maximum discharge of 15,568 cfs. Normal
reservoir storage as-built (original volume) is 9,900 acre-ft and maximum storage is 22,400 acre-ft
(USEPA, 1999b.). Siltation of the reservoir has resulted in current storage volume of 6,324 acre-ft
(Illinois State Natural History Survey, 1994) to 4,874 acre-ft (Bond County SWCD, 1999) or a reduction
20 30 40 50 60 70 80 90
Low Nutrients High Nutrients
Oligotrophic Mesotrophic Eutrophic Hypereutrophic
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