2.7.10.1. About Dunns Creek/Crescent Lake
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- East of the St. Johns River in Flagler County
- Primary Land Use: Forested/Wetlands
- Current TMDL reports:
Nutrient (2606B) - 2022 Verified Impairment for Nutrients (Chlorophyll-a) (2606A) and Fecal coliform (2606A)
- WBID Area: 585 sq. mi.
- Beneficial Use: Class III F (Recreational – Freshwater)
2.7.10.2. Data sources
Data were historically downloaded from the FL STORET website (DEP 2010f), with recent data downloaded from WIN WAVES (DEP 2022f). Data were filtered based on the stations in the Dunns Creek/Crescent Lake WBIDs 2606A/B (DEP 2023b) shown above. The filtered dataset reflects water column concentrations and was used to generate Table 2.15, with freshwater stream WQC’s generally reported; the listed WQC for total phosphorus is the site-specific alternative criterion for average total phosphorus levels in colored lakes. These should be regarded as guidelines only because Dunns Creek (2606A) is accessed as a stream, Crescent Lake (2606B) is accessed as a lake and has different WQC’s.
2.7.10.3. Discussion
Water quality data for Dunns Creek/Crescent Lake are shown in Table 2.15. Dunns Creek (WBID 2606A) was identified as being impaired for mercury, based on elevated levels of mercury in fish tissue, however this was delisted (DEP 2016f) as it has been addressed by the statewide mercury TMDL (DEP 2013c). This tributary is a significant non-point-source contributor to nutrient levels in the St. Johns River (Magley and Joyner 2008), and a TMDL for Nutrients was adopted (DEP 2021c) for Crescent Lake (2606B) based on its Trophic State Index (TSI), calculated from the total nitrogen (TN), total phosphorus (TP), and chlorophyll-a levels, with a 34% reduction in total nitrogen and 58% reduction in total phosphorus.
Dunn’s Creek (2606A) was listed as Impaired for nutrients (chlorophyll-a) and fecal coliform in 2022 (DEP 2016h; DEP 2020e; DEP 2022). The average total phosphorus concentrations remained above the site-specific criterion value (0.05 mg/L) from 2020-2022. Mean chlorophyll-a levels exceeded the WQC in 2020 and 2022 and were near the WQC in 2021. Fecal coliform data were not available for 2021-2022.
Table 2.15 Water quality data for Dunns Creek/Crescent Lake.
| Water Quality | Average and Number of Samples º | |||
|---|---|---|---|---|
| Parameter | Criteria (FW) | 2020 | 2021 | 2022 |
| Dissolved Oxygen (mg/L) | ≥34% sat. (≥3.0) | 7.5 (0 of 71 samples) | 7.41 (1 of 31 samples) | 6.70 ± 0.19 (0 of 36 samples) |
| Total Nitrogen (mg/L) | <1.54‡ | Not available | Not available | 1.32 ± 0.10 (3 of 10 samples) |
| Total Phosphorus (mg/L) | <0.05‡ | 0.11 (19 of 22 samples) | 0.07 (14 of 23 samples) | 0.09 ± 0.01 (9 of 10 samples) |
| Chlorophyll-a (µg/L) | <20‡ | 31.15 (13 of 22 samples) | 15.08 (3 of 11 samples) | 38.29 ± 5.38 (9 of 10 samples) |
| Arsenic (µg/L) | ≤50 | 2.75 (0 of 11 samples) | 2.33 (0 of 6 samples) | 2.25 ± 0.50 (0 of 5 samples) |
| Cadmium (µg/L) | ≤0.3 | 0.05 (0 of 11 samples) | 0.03 (0 of 6 samples) | 0.03 ± 0.000 (0 of 5 samples) |
| Copper (µg/L) | ≤9.3 | 1.84 (0 of 11 samples) | 2.33 (0 of 6 samples) | 0.75 ± 0.50 (0 of 5 samples) |
| Iron (mg/L) | ≤1 | Not included in 2021 SORR | Not included in 2022 SORR | 0.20 ± 0.05 (0 of 5 samples) |
| Lead (µg/L) | ≤3.2 | 0.3 (0 of 11 samples) | 0.32 (0 of 6 samples) | 0.28 ± 0.000 (0 of 5 samples) |
| Nickel (µg/L) | ≤52 | 0.48 (0 of 11 samples) | 0.25 (0 of 6 samples) | 0.25 ± 0.000 (0 of 5 samples) |
| Silver (µg/L) | ≤0.07 | 0.05 ( 1 of 11 samples) | 0.03 (0 of 6 samples) | 0.03 ± 0.000 (0 of 5 samples) |
| Zinc (µg/L) | ≤120 | 2.5 ( 0 of 11 samples) | 2.50 (0 of 6 samples) | 2.50 ± 0.000 (0 of 5 samples) |
| Fecal Indicator Bacteria (E. coli) (CFU/100 mL) | E. coli <410 | 11 ( 0 of 10 samples) | Not available | Not available |
| Turbidity (NTU) | <29 | 7.73 (0 of 18 samples) | 2.86 (0 of 10 samples) | 6.12 ± 0.42 (0 of 9 samples) |
° = Number of samples below Water Quality Criteria for Dissolved Oxygen; Number of samples above Water Quality Criteria for all other parameters.
FW = freshwater; SW = saltwater (marine). Values denoted with (*) indicate a proposed criterion, which has not yet been adopted.
Values denoted with (‡) are reference values based on EPA criteria (EPA 2010b), but the water body is not regulated by this standard.