Browns Lake IA 06-WEM-1735
Woodbury County S32T87NR47W 2 mi W of Salix.
- Cycle
- 2022
- Release Status
- Final
- Overall IR
- 5 - Water is impaired or threatened and a TMDL is needed.
- Trophic
- Hypereutrophic
- Trend
- Stable
- Created
- 1/4/2022 3:10:17 PM
- Updated
- 1/6/2022 10:37:53 AM
| Cycle Added | Class | Cause | Data Source | Rationale |
|---|---|---|---|---|
| 2016 | Class A1 | Algal Growth: Chlorophyll a | Ambient monitoring: Iowa DNR-lakes | New data: WQ improvement (chemical / physical / bacterial) |
The Class A1 use was assessed (monitored) as “not supported” due to poor water transparency and aesthetically objectionable conditions caused by algae blooms. The Class BLW use was assessed (monitored) as “fully supported.” All other designated uses were "not assessed."
Data Sources: Data Source Data Source ID Data Type Data Age Site ID Site
Name Site
Description Iowa DNR 6 WQ CY 2016-2019 22970001 Browns
Lake
Class A1 - Indicator Bacteria: Site ID Data Source ID # Samples per Year (2018/ 2019/2020) 2018 Geometric Mean 2019 Geometric Mean 2020 Geometric Mean Violates Annual Geometric Mean? # 2018 SSM violations / SSM Violations needed for impairment # 2019 SSM violations / SSM Violations needed for impairment # 2020 SSM violations / SSM Violations needed for impairment Violates Annual SSM Significantly >10% Rule? Assessment Type Support Level 22970001 6 3/3/0 3 16 NA NO 0 / NA 0 / NA NA NO Evaluated Full Class A1 - pH: Site ID Data Source ID # Samples / # Years Minimum Value Maximum Value Mean Value # Violations Violations needed for impairment Violates Significantly >10% Rule? Assessment Type Support Level 22970001 6 12 / 4 8 8.7 8.3 0 4 NO Monitored Full Class A1 - Lake TSI's: Site ID Data Source ID Parameter Name # Samples / # Years Minimum Value Maximum Value Median Value Median TSI Violation? Assessment Type Support Level 22970001 6 Chlorophyll a TSI 12 / 4 44 75 56 NO Monitored Full 22970001 6 Secchi TSI 12 / 4 55 83 74 YES Monitored Not 22970001 6 Total Phosphorus TSI 12 / 4 67 82 76 NA NA NA 22970001 6 Inorganic suspended solids 12 / 4 0.6 30 13.5 NA NA NA DNR's assessment methodology indicates that at least two
assessment/listing cycles with a TSI value less than or equal to 63 are
necessary to suggest de-listing of an impairment. The chlorophyll a
TSI value for the 2016 assessment listing cycle was 67, which based on DNR's
assessment/listing methodology indicated an impairment based on the narrative
criteria protecting against aesthetically objectionable conditions. Because the
TSI value for the 2020 assessment/listing cycle was less than the trigger of 65
(2020 listing for chlorophyll a was 63), and because the TSI value for the
current listing cycle is also 56, based on DNR's methodology, these values
suggest "full support" of the Class A1 uses protecting against
aesthetically objectionable conditions and the impairment (5a) for chlorophyll
a is suggested for delisting for the 2022 assessment/listing cycle. Class BLW - Conventional Parameters: Site ID Data Source ID Parameter Name # Samples / # Years Minimum Value Maximum Value Mean Value # Violations # Acute / Chronic Violations Violations needed for impairment Violates Significantly >10% Rule? Assessment Type Support Level 22970001 6 Ammonia 12 / 4 0.0003 0.267 0.09 NA 0 / 0 4 NO Monitored Full 22970001 6 Dissolved Oxygen 12 / 4 6.7 12.1 8.8 0 NA / NA 4 NO Monitored Full 22970001 6 pH 12 / 4 8 8.7 8.3 0 NA / NA 4 NO Monitored Full 22970001 6 Temperature 12 / 4 14.9 28.1 22.7 0 NA / NA 4 NO Monitored Full Class BLW - Lake Planktonic Cyanobacteria: Site ID Data Source ID # Samples Maximum Cyanobacteria Wet Mass Maximum Cyanobacteria % Composition Median Cyanobacteria Wet Mass Median Cyanobacteria % Composition Median Cyanobacteria Concentration = 75th Percentile Assessment Type Support Level 22970001 6 6 27.33 57.6% 13.91 47.7% NO Evaluated NA Class HH: No Data The Class HH "full support" based on fish tissue monitoring was removed based on the age of the data.