Elm Lake IA 02-IOW-657
Wright County S21T92NR24W 1 mi. S of Cornelia.
- Assessment Cycle
- 2024
- Release Status
- Pending
- Data Collection Period
- Overall IR Category
- 5 - Water is impaired or threatened and a TMDL is needed.
- Trophic
- Hypereutrophic
- Trend
- Stable
- Created
- 11/14/2023 3:03:23 PM
- Updated
- 2/5/2024 12:43:11 PM
| Cycle Added | Class | Cause | Data Source | Rationale |
|---|---|---|---|---|
| 2020 | Class BLW | pH | Ambient monitoring: Iowa DNR-shallow lakes & wetlands | New data: WQ improvement (chemical / physical / bacterial) |
The Class BLW use was assessed as "not supported" due to high levels of total suspended solids that lead to an impairment of the narrative criteria protecting against undesirable or nuisance aquatic life. High levels of algae at this shallow lake also suggested impairment due to aesthetically objectionable conditions. 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 2018-2022 22990006 Elm Lake
Class BLW – Shallow Lake TSI: Site ID Data Source ID Parameter Name # Samples / # Years Minimum Value Maximum Value Median Value Median TSI Violation? Assessment Type Support Level 22990006 6 Chlorophyll a TSI 19 / 4 32 87 75 YES Mon Not The TSI value for Secchi depth is not used to evaluate the
attainment of the aquatic life use in shallow lakes. Due to the depth of these
shallow lakes, TSI values for Secchi depth can be misleading. In some
instances, the Secchi disk remains visible at the bottom of the lake and the
depth of the lake is recorded as the Secchi depth. In these instances, water
clarity may be sufficient to support the Class BLW use, but the index value is
limited by the depth of the lake. Thus, the combination of total suspended
solids and chlorophyll a was used to determine whether or not the Class BLW use
was impaired in these shallow systems. Class BLW - Binomial 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 22990006 6 Dissolved Oxygen 19 / 4 5.18 13.24 8.43 0 NA / NA 5 NO Mon Full 22990006 6 pH 13 / 3 7.71 8.99 8.31 0 NA / NA 4 NO Mon Full 22990006 6 Temperature 19 / 4 11.9 28.6 21 0 NA / NA 5 NO Mon Full Elm Lake was assessed as "not supported" for the 2020 assessment/listing cycle due to frequent violations of the state Class BLW criterion for pH. Based on DNR’s assessment methodology the current assessment/listing cycles must have fewer violations of the criterion based on the minimum required by the 10% Rule to propose delisting pH. There were less than 10% of the samples exceeding the single-sample maximum criterion for the 2024 assessment/listing cycle. Therefore, the impairment for pH is suggested for delisting for the 2024 assessment/listing cycle. Class BLW - Protection of Submerged Aquatic Vegetation: Site ID Data Source ID Parameter Name # Samples / # Years Minimum Value Maximum Value Median Value Median Value >=SAV Assessment Type Support Level 22990006 6 Total suspended solids 19 / 4 0.6 86 44 Yes Mon Not Guidelines for wetland assessment from the Upper Mississippi
River Conservation Committee’s Water Quality Technical Section (2003) state
that a median total suspended solids concentration during the growing season of
less than 30 mg/L is necessary to provide sufficient water clarity to support
the growth of submersed aquatic vegetation (SAV) in wetlands and shallow lakes.
High levels of total suspended solids impede the growth of SAV. SAV is critical
to the health of wetland and shallow lake ecosystems. The elimination of SAV
can degrade habitat quality such that undesirable aquatic species such as
cyanobacteria, common carp and fathead minnows dominate. As such, the
suppression of SAV constitutes a violation of Iowa’s narrative water quality
criteria protecting against undesirable or nuisance aquatic life. Class BLW - Toxic Parameters: Site ID Data Source ID Parameter Name # Samples / # Years Maximum Value Mean Value Median Value # Acute / Chronic Violations >1 Acute / Chronic Violation Assessment Type Support Level 22990006 6 Ammonia 8 / 2 0.67 0.18 0.02 0 / 0 NO Evaluated Full Class HH - No Data Note: Additional monitoring of fish and aquatic vegetation
populations at Elm Lake by DNR staff also suggested that the high levels of
total suspended solids and algae have adverse effects on fish populations and
limit the production of rooted aquatic vegetation in this wetland. These results
further indicated that the aquatic life use of this wetland should be assessed
as "not supported."