Hawthorn Lake IA 03-NSK-862

Mahaska County S10T77NR14W 1 mi S of Barnes City.

Open Data Collection Period Modal

For purposes of developing stream/river water quality assessments for integrated reporting, three years of water quality data are typically used for both conventional pollutant parameters (e.g., indicator bacteria) and the less frequently monitored toxic parameters (e.g., toxic metals). Since the 2004 IR cycle, DNR has used a three-year data gathering period for streams, rivers, and beaches. For most assessments, the use of three years of data increases the number of samples upon which the decision on use support is based and helps address the problem of weather-related year-to-year fluctuations in water quality.

Due to the lower sampling frequency in Iowa’s ambient lake, biological, fish kill, and fish tissue monitoring programs, five years of data are used for developing IR assessments and for identifying Section 303(d) listings.

Data Type	Data Timeframe
Beach Sampling Data	CY 2014 - 2016
Stream/River Water Quality Data	CY 2014 - 2016
Lake Water Quality Data	CY 2012 - 2016
Biological Sampling Data	CY 2012 - 2016*
Fish Kill Data	CY 2012 - 2016
Fish Tissue Sampling Data	CY 2012 - 2016
Continuous Dissolved Oxygen Sampling Data	CY 2012 - 2016
*Biological sites sampled in both 2011 and 2015 were also assessed.

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Cycle: 2018
Release Status: Final
Overall IR: 5 - Water is impaired or threatened and a TMDL is needed.
Trophic: Eutrophic
Trend: Stable
Created: 4/3/2019 2:01:32 PM
Updated: 3/29/2024 10:46:49 AM

Use Support

Class A1

Recreation - Primary contact

Partially Supported

Algal Growth: Chlorophyll a

Support Level

Partially Supported

Impairment Code

5a - Pollutant-caused impairment. TMDL needed.

Cause Magnitude

Moderate

Status

Continuing

Source

Natural: Internal Nutrient Recycling (Primarily Lakes)

Source Confidence

Moderate

Cycle Added

2010

Impairment Rationale

Narrative criteria violation: aesthetically objectionable conditions

Data Source

Ambient monitoring: Iowa DNR-lakes

TMDL Priority

Tier I

Class BLW

Aquatic Life - Lakes and wetlands

Fully Supported

Class HH

Human Health -

Not Assessed

General Use

General Use water -

Not Assessed

Impairment Delistings

No delistings for this assessment cycle.

Documentation

Assessment Summary

The Class A1 (primary contact recreation) uses are assessed (monitored) as “partially supported” due to aesthetically objectionable conditions caused by algal blooms. The Class B(LW) (aquatic life) uses are assessed (monitored) as “fully supported”. Fish consumption uses remain “not assessed” due to a lack of fish contaminant monitoring at this lake. Sources of data for this assessment include (1) results of the statewide survey of Iowa lakes conducted from 2012 through 2016 by Iowa State University (ISU), and (2) information from the IDNR Fisheries Bureau as summarized by Flammang and Ellison (2008).

Assessment Explanation

For the 2018 assessment/listing cycle, the Class A1 (primary contact recreation) uses of Hawthorne Lake are assessed (monitored) as "partially supported" based on information from the ISU lake survey. Using the median values from these surveys from 2012-2016 (approximately 15 samples), Carlson 's (1977) trophic state indices for Secchi depth, chlorophyll a, and total phosphorus were 63, 64, and 62 respectively for Hawthorne Lake. According to Carlson (1977) the Secchi depth, chlorophyll a, and total phosphorus values all place Hawthorne Lake in the Eutrophic category. These values suggest moderately high levels of chlorophyll a and suspended algae in the water, moderately poor water transparency, and moderately high levels of phosphorus in the water column. The data show one violation of the Class A1 criterion for pH in 15 samples (7%).

These results suggest "full support" of the Class A1 uses, however, Hawthorn Lake was listed as "partially supporting" the Class A1 uses for the 2016 assessment/listing cycle due to algal. Based on DNR's assessment methodology, median-based TSI values for chlorophyll a must be 63 or less for two consecutive assessment/listing cycles before a lake can be removed from the state's Section 303(d) list (IR Category 5). Therefore, Hawthorn Lake remains assessed as "partially supported" due to high levels of algae for the 2018 assessment cycle.

The level of inorganic suspended solids was relatively low at Hawthorne Lake, and does not suggest water quality problems due to non-algal turbidity. The median level of inorganic suspended solids in Hawthorne Lake (2.59 mg/L) was ranked 54th among the 138 lakes by the ISU lake survey.

Data from the 2012-2016 ISU lake survey suggest a moderately large population of cyanobacteria exists at Hawthorne Lake. These data show that cyanobacteria comprised 96% of the phytoplankton wet mass at this lake. The median cyanobacteria wet mass (24.6 mg/L) was ranked 93rd of the 138 lakes sampled.

The Class B(LW) (aquatic life) uses are assessed (monitored) as "fully supported." Results of the ISU lake survey from 2012-2016 show there were no violations of the criterion for ammonia in 15 samples(0%), no violations of the criterion for dissolved oxygen in 15 samples(0%), and one violation of the criterion for pH in 15 samples(7%). Based on DNR's assessment methodology these violations are not significantly greater than 10% of the samples and therefore suggest (fully supported/monitored) of the Class B(LW) uses of Hawthorne Lake.

Based on information from the DNR Fisheries Bureau [Flammang, M.and B.Ellison. 2008. Identification of the fishery and water quality status and needs of Hawthorn Lake, Iowa. Fisheries Bureau, Iowa DNR, 9 p.]. According tothe Lake Restoration Program2015 Report and 2016 Plan,Hawthorn Lake was drawn down in 2010 and watershed and lake restoration projects were completed throughout the assessment period.The DNR designed eight sediment control ponds for watershed improvement on public and privateground. Five of the eight structures on public property are now completed. Additionally,lakes fishery has redeveloped quickly following completion of the 2010 restorationproject.Largemouth bass abundance and quality are excellent.This suggests that the Class B(LW) (aquatic life) uses assessment should be assessed as(monitored) and "fullysupported”.

Fish consumption uses remain "not assessed" due to the lack of fish contaminant monitoring in this lake.

Note:A watershed assessment was completed in 2010. Multiple structures were completed since that time and 4 more are currently under construction. Sedimentation in the two main arms has been substantial and up to 20% of the storage capacity has been lost in those sections. The fish community was renovated in 2010.

Monitoring and Methods

Assessment Key Dates

6/18/2012

Fixed Monitoring Start Date

9/19/2016

Fixed Monitoring End Date

Methods

120

Surveys of fish and game biologists/other professionals

222

Non-fixed-station monitoring (conventional during key seasons and flows)

340

Primary producer surveys (phytoplankton/periphyton/macrophyton)