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 2020 - 2022
Stream/River Water Quality Data	CY 2020 - 2022
Lake Water Quality Data	CY 2018 - 2022
Biological Sampling Data	CY 2018 - 2022*
Fish Kill Data	CY 2018 - 2022
Fish Tissue Sampling Data	CY 2018 - 2022
Continuous Dissolved Oxygen Sampling Data	CY 2018 - 2022
*Biological sites sampled in both 2017 and 2021 were also assessed.

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Cycle: 2024
Release Status: Final
Overall IR: 5 - Water is impaired or threatened and a TMDL is needed.
Trophic: Eutrophic
Trend: Stable
Created: 12/14/2023 1:39:46 PM
Updated: 3/29/2024 10:48:03 AM

Use Support

Class A1

Recreation - Primary contact

Not Supported

Algal Growth: Chlorophyll a

Support Level

Not Supported

Impairment Code

5* - 303(d)-impaired last cycle; fully supporting this cycle; potential de-listing.

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

WINOFI

Algal Growth: Cyanobacteria

Support Level

Further Investigation Needed

Impairment Code

3b - Use potentially impaired based on an evaluated assessment.

Cause Magnitude

Slight

Status

Continuing

Source

Agriculture

Source Confidence

Moderate

Cycle Added

2022

Impairment Rationale

Adverse impacts on plant/animal communities

Data Source

Ambient monitoring: Iowa DNR-lakes

Class HH

Human Health -

Not Assessed

Impairment Delistings

No delistings for this assessment cycle.

Documentation

Assessment Summary

The Class A1 use remains as “not supported” due to aesthetically objectionable conditions caused by algal blooms until the TMDL study currently in process is completed. The Class BLW use was assessed (evaluated) as “WINOFI” due to cyanobacteria blooms. All other designated uses were “not assessed.”

Assessment Explanation

Data Sources:

Data Source	Data Source ID	Data Type	Data Age	Site ID	Site Name	Site Description
Iowa DNR	6	WQ	CY 2018-2018	14000239	Hawthorn 2
Iowa DNR	6	WQ	CY 2018-2022	22620001	Hawthorn Lake

Class A1 - Indicator Bacteria: No Data

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
14000239	6	10 / 1	7.55	9.26	8.29	1	3	NO	Mon	Full
22620001	6	25 / 5	7.4	9.1	8.3	2	5	NO	Mon	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
14000239	6	Chlorophyll a TSI	10 / 1	57	74	64	NO	Evaluated	Full
22620001	6	Chlorophyll a TSI	26 / 5	35	74	62	NO	Mon	Full
14000239	6	Secchi TSI	10 / 1	55	76	63	NO	Evaluated	Full
22620001	6	Secchi TSI	26 / 5	49	76	64	NO	Mon	Full
14000239	6	Total Phosphorus TSI	10 / 1	61	74	65	NA	NA	NA
22620001	6	Total Phosphorus TSI	26 / 5	49	73	62	NA	NA	NA
22620001	6	Inorganic suspended solids	15 / 5	0.6	13	4	NA	NA	NA

Although the index value for Chlorophyll a was below the impairment threshold of 65 for this assessment cycle, the Class A1 use of Hawthorn Lake remains “not supported” until the TMDL study currently in process is completed.

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
14000239	6	Dissolved Oxygen	10 / 1	5.17	14.08	8.6	0	NA / NA	3	NO	Mon	Full
22620001	6	Dissolved Oxygen	25 / 5	4.4	12.7	8.1	2	NA / NA	5	NO	Mon	Full
14000239	6	pH	10 / 1	7.55	9.26	8.29	1	NA / NA	3	NO	Mon	Full
22620001	6	pH	25 / 5	7.4	9.1	8.3	2	NA / NA	5	NO	Mon	Full
14000239	6	Temperature	10 / 1	11.7	28.5	22.2	0	NA / NA	3	NO	Mon	Full
22620001	6	Temperature	25 / 5	12	29.5	23.6	0	NA / NA	5	NO	Mon	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
22620001	6	5	193.1284185	98%	43.11786597	84%	YES	Evaluated	3b

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
14000239	6	Ammonia	9 / 1	0.3	0.1	0.02	0 / 0	NO	Evaluated	Full
22620001	6	Ammonia	23 / 5	0.35	0.09	0.02	0 / 0	NO	Mon	Full

Class HH - Toxic Parameters: No Data

Monitoring and Methods

Assessment Key Dates

4/30/2018

Monitoring Start

9/27/2022

Monitoring End

Methods

200

Physical/Chemical Monitoring

340

Primary producer surveys (phytoplankton/periphyton/macrophyton)