Elm Lake IA 02-IOW-657
Wright County S21T92NR24W 1 mi. S of Cornelia.
- Assessment Cycle
- 2020
- Release Status
- Final
- Data Collection Period
- Overall IR Category
- 5 - Water is impaired or threatened and a TMDL is needed.
- Trend
- Stable
- Created
- 7/22/2020 3:17:43 PM
- Updated
- 10/13/2020 1:11:55 PM
The Class BLW use is assessed as "not supported" due to high levels of total suspended solids that leads to an impairment of the narrative criteria protecting against undesirable or nuisance aquatic life and due to violations of the Class BLW criterion for pH. High levels of algae at this wetland also suggest impairment due to aesthetically objectionable conditions. All other designated uses are “not assessed”.
Sources of
Data: Data Source Data Source ID Data Type Data Age Site ID Site Name Site Description Iowa DNR 6 WQ CY 2016-2018 22990006 Elm Lake
Class BLW - TSI's 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 15 / 3 32 82 68 YES Monitored Not 22990006 6 Inorganic suspended solids 15 / 3 0.06 69.2 16 NA NA NA The TSI
value for Secchi depth is not used to evaluate the attainment of aquatic life
goals 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 uses, but the index value is limited by the depth of the lake.
Thus the combination of total suspended solids and chlorophyll a will be used
to determine whether or not the Class BLW uses are impaired in these shallow
systems. Class BLW -
Conventional Parameters: Site ID Data Source ID Parameter Name # Samples / # Years Maximum Value Mean Value Median Value # Acute / Chronic Violations % Acute/ Chronic Violations Significantly >10% Violations Assessment Type Support Level 22990006 6 Ammonia 10 / 2 0.36195 0.14 0.03 0 / 1 0% / 10% NO Monitored Full 22990006 6 Dissolved oxygen 9 / 2 9.36 8.05 7.91 NA / 0 NA / 0% NO Evaluated Full 22990006 6 pH 10 / 2 11.8 9.14 8.96 4 / NA 40% / NA YES Monitored Not 22990006 6 Temperature 10 / 2 28 23 23 0 / 0 0% / 0% NO Monitored Full 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 15 / 3 0.6 122.5 31 Yes Monitored Not Guidelines
for wetland assessment from the Upper Mississippi River Conservation
Committee’s Water Quality Technical Section (2003) state that an average 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 in wetlands and shallow lakes. High levels of
total suspended solids impede the growth of submersed aquatic vegetation (SAV).
Submersed aquatic vegetation 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 HH - No
Data Note: Additional monitoring of fish and aquatic vegetation populations at Elm Lake by DNR staff also suggests 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 indicate that the aquatic life uses of this wetland should be assessed as "not supported."