Clean Water Partnership Diagnostic Study

PROJECT SPONSOR: Crow Wing County, Minnesota: Chris Pence, Environmental Services Director. CONTRIBUTING SUPPORTERS: City of Crosby, Joel Peck, City Administrator; Crow Wing Soil and Water Conservation District, Melissa Barrick, District Manager; and Serpent Lake Association. MPCA Program Manager: Bonnie Finnerty June 30, 2013

Serpent Lakeshed Protection Investigation Study

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1.0 Table of Contents

1.0 Table of Contents ................................................................................................................. 2

List of Tables, Figures, and Maps ................................................................................................ 4

2.0 Executive Summary .............................................................................................................. 1

2.1 Diagnostic Study ............................................................................................................... 1

3.0 Introduction and Project Background.................................................................................. 1

3.1 History of the water(s) of concern and project area ....................................................... 1

3.1.1 Project area ........................................................................................................................... 1

3.1.2 Known water quality problems ............................................................................................. 2

3.1.3 Historical water quality projects ........................................................................................... 3

3.1.4 Economic significance of the water of concern .................................................................... 3

3.2 Why the project took place .............................................................................................. 4

3.3 Who was involved in carrying out the project ................................................................. 4

3.4 Project costs by program element ................................................................................... 4

3.4.1 Element 1: Develop a project work plan ............................................................................... 5

3.4.2 Element 2: Monitoring program ........................................................................................... 6

3.4.3 Element 3: Modeling ............................................................................................................. 8

3.4.4 Element 4: Fiscal management and administration ............................................................. 8

3.4.5 Element 5: Community stakeholder meetings ..................................................................... 8

3.4.6 Element 6: Final Report submittal ........................................................................................ 8

4.0 Project Milestones ............................................................................................................... 9

5.0 Methods ............................................................................................................................. 10

5.1 Water quality monitoring ............................................................................................... 10

5.1.1 Water quality characterization goals .................................................................................. 10

5.1.2 Water quality monitoring methods .................................................................................... 10

5.1.3 Water quality monitoring quantitative goals ...................................................................... 11

5.2 Watershed assessment .................................................................................................. 11

5.3 Quality control/quality assurance (field, laboratory, and office) .................................. 12

5.4 Water modeling techniques ........................................................................................... 12

6.0 Results ................................................................................................................................ 13

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6.1 Description of project area ............................................................................................ 13

6.1.1 Existing land use .................................................................................................................. 13

6.1.2 Soils ..................................................................................................................................... 14

6.1.3 Population characteristics ................................................................................................... 14

6.1.4 Lake development, property value and economic summary ............................................. 14

6.1.5 Community water supplies ................................................................................................. 14

6.1.6 Point Sources of pollution ................................................................................................... 15

(1) Wastewater and feedlots in the watershed ........................................................................... 15

6.2 Project data and information ......................................................................................... 15

6.2.1 Agricultural watershed assessment .................................................................................... 15

6.2.2 Urban watershed assessment ............................................................................................. 16

6.2.3 Regional runoff and precipitation ....................................................................................... 17

(1) Climate Change ....................................................................................................................... 18

6.2.4 Aquifer assessment ............................................................................................................. 19

6.3 Description of the water(s) of concern .......................................................................... 19

6.3.1 Morphometric data ............................................................................................................. 19

(1) Lake morphometric characteristics......................................................................................... 19

6.3.2 Monitoring stations and sample inventory by tributary, storm ......................................... 20

6.3.1 In-lake samplings ................................................................................................................. 20

6.3.2 Long-term monitored total phosphorus, Chlorophyll-a and Secchi Transparency ............. 20

6.3.3 2012 Total Phosphorus, Chlorophyll-a and Secchi Transparency ...................................... 22

6.3.4 Dissolved oxygen and temperature diagrams .................................................................... 24

6.3.5 Secchi transparency plots ................................................................................................... 26

6.3.6 Map of monitoring network: See Figure 12 ........................................................................ 26

6.3.7 Water balances for the study period .................................................................................. 27

6.4 Peterson Creek ............................................................................................................... 27

6.4.1 Flow-weighted mean concentrations of measured parameters by tributary .................... 29

6.4.2 Nutrient balances ................................................................................................................ 29

7.0 Discussion........................................................................................................................... 32

7.1 Assessment of the project's resource water quality ...................................................... 32

7.2 Assessment of pollutant loads ....................................................................................... 32

7.3 Resource water quality goals ......................................................................................... 32

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7.4 Target reductions of pollutants needed to meet water quality goals ........................... 33

8.0 Conclusions ........................................................................................................................ 34

8.1.1 Future Management Goal Recommendations: .................................................................. 34

9.0 References ......................................................................................................................... 35

10.0 Distribution List .................................................................................................................. 35

List of Tables, Figures, and Maps Figure 1. Minor Watershed 10090 contributes water to Serpent Lake. ........................................ 2

Figure 2. Upper Mississippi Basin and the Mississippi River-Brainerd Watershed. ....................... 2

Figure 3. The Rabbit River Lakeshed (1009005; Aerial Imagery 2008; 1m). .................................. 2

Figure 4 Map of Serpent Lake illustrating bathymetry, lake sample site locations, stream inlets and outlets and aerial land use. ...................................................................................................... 3

Figure 5. Project Organization ........................................................................................................ 4

Figure 6. Map of sampling locations ............................................................................................. 11

Figure 7 Land Cover Classification ................................................................................................ 13

Figure 8 Deerwood Drinking Water Supply Management Area ................................................... 15

Figure 9 Permitted feedlots in the Serpent Lake Watershed ....................................................... 16

Figure 10 2000 impervious cover of the Serpent Lakeshed ......................................................... 17

Figure 11. Serpent Lake (Riverton) Rainfall (2012) ....................................................................... 18

Figure 12. Serpent Lake and Watershed Monitoring Network .................................................... 20

Figure 13. Seasonal Trends in Chlorophyll-a (2012) ..................................................................... 23

Figure 14. Seasonal Trends in Total and Ortho Phosphorus (2012) ............................................ 23

Figure 15. Temperature and Dissolved Oxygen by depth at Site 203 (May 7, 2012) ................... 24

Figure 16. Temperature and Dissolved Oxygen by depth at Site 203 (June 26, 2012) ................ 25

Figure 17. Temperature and Dissolved Oxygen by depth at Site 203 (August 29, 2012) ............. 25

Figure 18. Temperature and Dissolved Oxygen by depth at Site 203 (September 20, 2012) ...... 26

Figure 19. Secchi Transparency Long-term Trends ....................................................................... 26

Figure 20. 2011-2012 Peterson Creek Flows Monitored by the MPCA and daily rainfall totals . 28

Figure 21. Serpent Lake Levels, Volunteer Monitoring (2012) ..................................................... 28

Figure 22. Serpent Lake BATHTUB loading general sensitivity to increases or decreases in total phosphorus loads. ......................................................................................................................... 34

Table 1. Carlson Trophic Index; Years monitored: 1977-1981, 2002-2008 .................................... 2

Table 2 Project Costs by Program Element ..................................................................................... 5

Table 3. Peterson Creek Site (S006-784) Samples and Duplicate Samples .................................... 6

Table 4. Stormwater Sampling Events ............................................................................................ 7

Table 6 Serpent Lakeshed Lake Testing .......................................................................................... 8

Table 5.Serpent Lake Profiling (Lake ID #18-0090, Site 202 and 203) ............................................ 7

Table 7. Project Milestones ............................................................................................................ 9

Table 8. Monitoring sites .............................................................................................................. 10

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Table 9. Key to monitoring map ................................................................................................... 11

Table 10 Land use Serpent Lakeshed 1990 to 2000 ..................................................................... 16

Table 11. 1980-2012 Data Summary (from NOAA, 2012) ............................................................ 17

Table 12. 2002-2012 Warm Season and Annual Precipitation for Riverton, MN (MDNR Site 216972) ......................................................................................................................................... 18

Table 13. Serpent Lake Watershed Summary Morphometric Characteristics* ........................... 19

Table 14. Monitoring station average TP, OP, and TKN (2012) .................................................... 27

Table 15. Summary of Serpent Lake Runoff Used to Construct 2012 Water Budget .................. 27

Table 16. Peterson Creek flow and load summary ....................................................................... 27

Table 17. Peterson Creek flow and load summary ....................................................................... 29

Table 18. Monitoring station average TP, OP, and TKN (2012) .................................................... 29

Table 19. Summary of Serpent Lake Runoff Used to Construct 2012 Water Budget .................. 29

Table 20. Phosphorus Loading Estimated to Serpent Lake 2012 ................................................. 30

Table 21. BATHTUB model water and mass balances .................................................................. 31

Table 22. Phosphorus Loading Estimated to Serpent Lake 2012 ................................................. 32

Table 23. Distribution List ............................................................................................................. 35

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2.0 Executive Summary

2.1 Diagnostic Study Crow Wing County (CWC), Minnesota received a Minnesota Pollution Control Agency Clean Water Partnership (CWP) project grant in 2011 to complete a diagnostic study of the water quality of Serpent Lake. This Report is the final report for this study. The Report includes a summary of previous studies and reports completed for Serpent Lake and its watershed. Lake and tributary water quality data that has been archived since the 1970’s was retrieved and analyzed for water quality trends and current lake water quality status. Water quality data that was collected in 2011 and 2012 was analyzed and presented in this report. Long term data indicates that the water quality in Serpent Lake is declining. The lake water quality indicators are better than the large lake target levels reported by the MPCA; however, water quality trends show declining water quality from 2002-2012 compared to 1977-1981.

3.0 Introduction and Project Background

3.1 History of the water(s) of concern and project area

3.1.1 Project area Serpent Lake is located between the City of Crosby and City of Deerwood, in CWC (CWC), Minnesota. It covers 1,103 acres, which places it in the upper 10% of lakes in Minnesota in terms of size. Serpent Lake has one intermittent inlet on the east end and one intermittent outlet on the west end. The outlet, Serpent Creek, runs under the city of Crosby to Mahnomen Lake. From there the water eventually flows into the Mississippi River. Serpent Lake is found within the Upper Mississippi River Basin, which includes the Mississippi River-Brainerd Major Watershed as one of its sixteen major watersheds (Figure 2). The basin covers 20,000 square miles, while the Mississippi River-Brainerd Watershed covers 1,687 square miles (approximately 1,079,558 acres). Serpent Lake falls within minor watershed 10090, one of the 126 minor watersheds that comprise the Mississippi River-Brainerd Major Watershed (Figure 3). Serpent Lake falls within the Rabbit River (1009005) lakeshed, covering 3,316 acres which includes the lake area (Figure 1).

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3.1.2 Known water quality problems

Water quality data has been collected on Serpent Lake since 1977. The data shows that the lake is mesotrophic (TSI 40-50). Table 1 lists the water quality parameters and mean, maximum, and minimum concentrations. Site 201 has data from 1971-1981, 2002-2008 and Site 203 has data from 2003, 2005-

2008 (Error! Reference source not found.). The transparency data from site 201 was analyzed using the Mann Kendall Trend Analysis. This trend analysis indicated there is 99.9 percent probability that transparency readings are declining at site 201.

Table 1. Carlson Trophic Index; Years monitored: 1977-1981, 2002-2008

Parameters Site 201

Site 203

Total Phosphorus Mean (ug/L): 18.9 15.5

Total Phosphorus Min: 12.0 5.0

Total Phosphorus Max: 38.0 29.0

Number of Observations: 7 19

Chlorophyll a Mean (ug/L): 3.6 4.7

Chlorophyll-a Min: 1.0 1.0

Chlorophyll-a Max: 12.0 11.0

Number of Observations: 7 19

Secchi Depth Mean (ft): 17.1

Secchi Depth Min: 8.0

Secchi Depth Max: 30.0

Number of Observations: 131

Figure 2. Upper Mississippi Basin and the Mississippi River-Brainerd Watershed.

Figure 3. The Rabbit River Lakeshed (1009005; Aerial Imagery 2008; 1m).

Figure 1. Minor Watershed 10090 contributes water to Serpent Lake.

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3.1.3 Historical water quality projects

Serpent Lake Association (SLA) was established in 1975 and has built a very strong working relationship with the SWCD and LGUs. The gradual decline in the lake water quality and concern for lakeshore development and redevelopment caused SLA to seek help from the Minnesota Pollution Control Agency (MPCA), Minnesota Department of Natural Resources (DNR), and CWC. In spring 2009, SLA partnered with DNR, SWCD, Minnesota Board of Water and Soil Resources, City of Crosby, and local civic groups to complete a stormwater retrofit project. The project included valley gutters, two bioretention basins and a 300 feet shoreline buffer in an attempt to protect Serpent Lake from urban runoff. Furthermore, SWCD, MPCA, and SLA are currently monitoring Unnamed Cranberry Lake (18-0433) for phosphorus, chlorophyll-a, and secchi readings which will meet 303(c) or 303(d) state assessments in the Fall of 2011. In further outreach efforts in 2009, the SLA started a petition to request to raise a fee to improve the lake’s water quality by creating a Lake Improvement District. Citizens demonstrated their passion and high for the water quality of the lake when over sixty-two percent of Serpent Lake property owners signed the petition. The Lake Improvement District was not approved by CWC.

3.1.4 Economic significance of the water of concern

The Serpent Lakeshed is located in the heart of the Cuyuna Range State Recreation Area. This recreational area brings over 75,000 people annually for biking, swimming, fishing, and scuba diving which in turn contributes to the large tourism based economy of North Central Minnesota. With over

Figure 4. Map of Serpent Lake illustrating bathymetry, lake sample site locations, stream inlets and outlets and aerial land use.

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417 property owners around Serpent Lake the tax base along is a significant impact to the cities, townships, and the County. Collectively, the property tax value for the 417 parcels is over 1 million dollars in tax revenue according to CWC Assessors Property Tax Assessment 2013.

3.2 Why the project took place

The purpose of the project was to monitor major inflows and outflows of Serpent Lake, and to monitor Serpent, Unnamed Cranberry, Unnamed/Peterson, and Cascade Lakes; determining phosphorus and nutrient loads associated with the inflows and outflows; and using BATHTUB modeling to determine the transport of nutrients, water quality conditions, and responses to nutrient loads. Serpent Lake has transparency readings which are trending downward. This project better defined the sources and magnitudes of nutrients loads to Serpent Lake. Finally, the project created this report and an implementation plan to identify and prioritizes areas of concern along with corresponding corrective actions to be implemented within the lakeshed.

3.3 Who was involved in carrying out the project Melissa Barrick is responsible for project organization to include coordination with the Project Sponsor, Contributing Sponsor, Project Manager, subcontractor and citizen volunteers. Melissa worked with project sponsor Chris Pence, CWC Environmental Services Director and Jason Rausch, Auditor for fiscal affairs, Bonnie Finnerty, MPCA Project Manager and Rhonda Adkins, the MPCA Data Specialist. The project organization is outlined in Figure 5.

Figure 5. Project Organization

3.4 Project costs by program element

The grant amount of $42,744 covered 50% of the expenses for the project. Estimates for in-kind contributions are included in Table 2. Program elements for the Serpent Lake Protection Investigation Study are organized in six parts by discipline and function.

Project Sponsor Crow Wing County

Chris Pence Environmental Services Director

Serpent Lake Association Subcontractor EOR RMB Laboratories

Crow Wing SWCD

Melissa Barrick Project Manager

MPCA Project Manager

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1. Work Plan Development 2. Monitoring Program 3. Modeling 4. Fiscal Management and Administration 5. Community Stakeholder Meetings 6. Final Report Submittal

Table 2 Project Costs by Program Element

Element Item Grant Funds Spent

Cash Match

In-Kind Match Total Project Cost

1. Work Plan Development

$ 660.00 $450.00 $1,110.00

2. Monitoring Program

Monitoring Supplies & Shipping

$7,620.80 $450.00 $8,070.80

2. Monitoring Program

Serpent Lake Monitoring and QA/QC

$966.00 $2,328.00 $6,559.25 $9,853.25

2.Monitoirng Program

Peterson Creek sampling and QA/QC

$1,486.00 $1,585.00 $3,071.00

2.Monitoirng Program

Stormwater Sampling QA/QC

$2,076.00 $1,350.10 $3,426.10

2. Monitoring Program

Small Subwatershed lakes and QA/QC

$0.00 $1,200.00 $4,790.36 $5,990.36

2. Monitoring Program

Coordination and training

$6,360.00 0.00 $3,926.95 $10,286.95

2. Monitoring Program

Serpent Lake Outlet Measurements

0.00 0.00 $,2936.60 $2,936.60

3. Modeling EOR Contract $10,706.00 0.00 0.00 $10,706.00 4. Fiscal Management and Administration

Accounting Pay bills, semi and annual reporting

$4,829.20 $4,340.40 $6000.00 $15,169.60

5. Community Stakeholder Meetings

Coordinate an host community meetings

$1,800.00 $ 1,160.00 $5,315.00 $8,275.00

6. Final Report submittal

Writing Final Report

$6,240.00 $ 900.00 $7,140.00

Total $42,744.00 $9,028.40 $34,263.26 $86035.66

3.4.1 Element 1: Develop a project work plan

After the grant contract was executed, SWCD developed a project Work Plan that is in accordance with the contract and guidelines.

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3.4.2 Element 2: Monitoring program The monitoring program was organized in four units: Serpent Lake profiling and chemistry, lake chemistry for lakes within the lakeshed, flow measurements and chemistry, and rain sampling events (stormwater). The following tables describe the number of sites, number of samples, and cost per sample for Peterson

Creek (Table 43), Rain Event Samples (Stormwater; Error! Reference source not found.), Serpent Lake profiling and chemistry (Table 5.), and lake chemistry for lakes within the Lakeshed (Table 6). SWCD staff established all sites that were not established (Not Est.) in the MPCA STORET/EQuiS Database.

Table 3. Peterson Creek Site (S006-784) Samples and Duplicate Samples

Location Chemistry

Time Frame

Cost # Sites # of

Samples Number of years

Total Cost #

Dups. Cost of Dups.

Peterson Creek (S006-784)

TSS April & Oct. 2 x

per month $9.00 1 4 2 $72.00 1 $9.00

Peterson Creek (S006-784)

TSS May-Sept

2x a month

$9.00 1 10 2 $180.00 2 $18.00

Peterson Creek (S006-784)

TSVS May-Sept

2x a month

$18.00 1 10 2 $360.00 2 $36.00

Peterson Creek (S006-784)

TP May-Sept

2x a month

$12.00 1 10 2 $240.00 2 $24.00

Peterson Creek (S006-784)

TSS April & Oct. 2 x

per month $9.00 1 4 2 $72.00 1 $9.00

Peterson Creek (S006-784)

TKN May-Sept

2x a month

$14.00 1 10 2 $280.00 2 $28.00

Peterson Creek (S006-784)

N +N May-Sept

2x a month

$10.00 1 10 2 $200.00 2 $20.00

Peterson Creek (S006-784)

SRP May-Sept

2x a month

$9.00 1 10 2 $180.00 2 $20.00

Total $81.00 7 64 2 $1,512.00 13 $155.00

SLA volunteers took grab samples, transparency tube readings, photographs, and measured recreational suitability at the Peterson Creek outlet (S006-784). In addition, a continuous operating data logger was installed at the Peterson Creek location. MPCA staff monitored and maintained this equipment. Rhonda Adkins, MPCA entered flow data from Peterson creek and Serpent Creek site S004-304 into HYDSTRA. At Serpent Creek (S004-302) a staff gauge was installed. SLA volunteers and SWCD Staff took daily staff gauge readings. SWCD staff entered Peterson Creek (S006-784) data into EQuIS as required by the grant agreement.

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Stormwater Sampling Events Chemistry

Cost #

Sites # of

Samples # of

Years Total Cost # Dups.

Cost of Dups.

City of Crosby Park (S006-790), Unamed Cranberry Lake/Inlet to Serpent (S006-786),Stormwater culvert (SS00014), Peterson Creek (S006-784)

TSS $9.00 4 5 2 $360.00 4 $36.00

City of Crosby Park (S006-790), Unamed Cranberry Lake/Inlet to Serpent (S006-786),Stormwater culvert (SS00014), Peterson Creek (S006-784)

TSVS $18.00 4 5 2 $720.00 4 $72.00

City of Crosby Park (S006-790), Unamed Cranberry Lake/Inlet to Serpent (S006-786),Stormwater culvert (SS00014), Peterson Creek (S006-784)

TP $12.00 4 5 2 $480.00 4 $48.00

City of Crosby Park (S006-790), Unamed Cranberry Lake/Inlet to Serpent (S006-786),Stormwater culvert (SS00014), Peterson Creek (S006-784)

SRP $9.00 4 5 2 $360.00 0 $0.00

Total $48.00 16 20 $1,920.00 12 $156.00

SLA volunteers took rain event SLA volunteers took grab samples five times per year for two years at the Cascade Outlet/Serpent Lake Inlet (S006-786), Crosby City Park (S006-790), stormwater pipe in City of Crosby (SS00014), and the Peterson Creek (S006-784) site. Rain event is defined as greater than 1” rainfall. For map of the specific sites see Figure 5.

The SWCD and SLA volunteers used a YSI 6820 sonde to collect dissolved oxygen and temperature every one meter on Serpent Lake (18-0090) site 202 and 203 (Figure 5). The SWCD used a Van Dorn to collect soluble reactive phosphate one foot to one meter above the bottom of the lake. Samples were analyzed for total phosphorus, soluble reactive phosphate, chlorophyll a, and transparency.

Serpent Lake Sites Lake Chemistry

Time Frame Cost # Sites # of Samples

Number of years

Total Cost # dups. Cost of Dups.

18-0090 Site 202 & 203

TP May-Sept 2x per month

$12.00 2 4 1 $96.00 0 $0.00

18-0090 Site 202 & 203

SRP May-Sept 2x per month

$9.00 2 18 1 $324.00 6 $54.00

18-0090 Site 202 & 203

SRP May-Sept 2x per month

$10.00 2 20 1 $400.00 2 $20.00

18-0090 Site 202 & 203

Chl-A May-Sept 2x per month

$18.00 2 2 1 $72.00 0 $0.00

Total per site, per sample $39.53 8 44 2 $892.00 8 $74.00

Table 4. Stormwater Sampling Events

Table 5.Serpent Lake Profiling (Lake ID #18-0090, Site 202 and 203)

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Table 6 Serpent Lakeshed Lake Testing

Small Lakes Parameter

s Time Frame Cost

# of Site

s

# of samples

# of Years

Total Cost

# Dups. Cost of Dups.

Unnamed/Peterson (18-0504-00-201)

TP, Chl-a, Secchi

May-Sept. 1x per month

$40.00 1 5 2 $400.00 1 $40.00

Unnamed Cranberry (18-0504-00-201)

TP, Cl-a, Secchi

May,Sept. 1x per month

June-August 2x per month

$ 40.00 1 8 2 $640.00 1 $40.00

Cascade (18-0061-00-201)

TP, Cl-a, Secchi

May-Sept. 1x per month

$40.00 1 5 2 $400.00 2 $80.00

Total 3 18 $1440.00 4 $160.00

The SLA volunteers used integrated samplers to take samples for total phosphorus, chlorophyll-a, secchi disc readings, and recreational suitability on Unnamed/Peterson (18-0504-201), Unnamed Cranberry (18-0504-201), and Cascade (18-0061-201) lakes. The additional data will be used in the model.

3.4.3 Element 3: Modeling

The Crow Wing SWCD provided monitoring data to Emmons & Olivier Resources (EOR), including stream discharge at Peterson Creek and at the Serpent Creek Site S004-302, stream inlets; and stormsewer discharge water quality data, and in-lake water quality data. Annual phosphorus loading to the lake from the monitored subwatersheds was estimated from the monitoring data, using a FLUX model. Phosphorus loading from the unmonitored subwatersheds was estimated by applying the calculated loading rates from the monitored subwatersheds. An in-lake response model was developed using the Bathtub model. The model was calibrated to the monitoring data collected for this project (2011 and 2012). The model was used to predict the response of Serpent Lake’s in-lake water quality if subjected to increases and decreases in phosphorus loading to the lake, and to determine the phosphorus load reductions needed for the lake to meet the water quality goals. These load reductions are the target load reductions for the implementation plan.

The modeling results are included in Section 6.0 Results.

3.4.4 Element 4: Fiscal management and administration

The SWCD established a process with the Fiscal Agent for handling financial commitments and payments, including submittal of financial plans and approved invoices for payment. The SWCD worked with the grant sponsor, laboratory, lake association, and EOR, to pay all bills associated with this project. Data for progress, semi-annual and final reports was collected, prepared and submitted to the Project Sponsor.

3.4.5 Element 5: Community stakeholder meetings

The SWCD coordinated and hosted three community stakeholders meetings. First meeting was held summer 2011, second meeting was spring 2012, and spring 2013. Meetings included local government unit staff, citizens, Serpent Lake Associations representatives, and elected officials. We had over 150 people attend the community stake holder meetings.

3.4.6 Element 6: Final Report submittal

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The SWCD worked with EOR to provide the overall final project report utilizing the information provided by CWC administration, historical background information, and the modeling results from the current project. The SWCD used the basic reporting requirements found in the documents on the MCPA website at http://www.pca.state.mn.us/index.php/water/water-types-and-programs/water-nonpoint-source-issues/clean-water-partnership/final-report-guidance-and-requirements-for-cwp-319-and-tmdl-study-. The project sponsor provided the needed semi-annual reports to the MPCA.

4.0 Project Milestones

Table 7. Project Milestones

Element Task Reasonability Time Frame Work Plan Development

Complete work plan

SWCD March, 2011

Monitoring Program Complete QAPP SWCD March-April 2011 Monitoring Program Visit all Stream

Sites MPCA and SWCD April, 2011

Monitoring Program Establish new sites SWCD May, 2011 Monitoring Program Train Volunteers SWCD March-May, 2011 Monitoring Program Coordinate

monitoring schedule

SWCD

Monitoring Program Collect Water samples and staff gauge readings

SWCD & Volunteers April-Oct 2011 and 2012

Monitoring Program Enter Data into STORET/EQuiS

SWCD, SLA and RMB Labs November 2011 & 2012

Fiscal Management and Administration

Pay bills SWCD Continually

Complete all annual and semi-annual reporting

SWCD Semi-annually

Community Task Meetings

Coordinate community task meetings

SWCD

Host community task meetings

SWCD, NRCS, MPCA, and MNDNR, Citizen groups

Semi-annually

Final Report Compile data for final report

EOR Subcontractor, SWCD, NRCS, MPCA, SLA

December 2012

Write and submit final report

EOR Subcontractor, SWCD, MPCA

Fall 2012-Spring 2013

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5.0 Methods

5.1 Water quality monitoring

5.1.1 Water quality characterization goals Objective 1: Characterize the chemical and physical water quality of the major streams and smaller lakes that feed into Serpent Lake. Objective 2: Model Serpent Lake using the BATHTUB model to understand how much loading Serpent Lake is able to handle to help guide future implementation. The purpose of this project is to provide a chemical and physical water quality baseline over two years. In addition, continued lake monitoring with the addition ofdept profiling will provide data to do BATHTUB modeling for water and nutrient balance, nutrient and chlorophyll a concentration, and oxygen depletion.

5.1.2 Water quality monitoring methods

The monitoring program was organized in four units; Serpent Lake depth profiling and chemistry, lake chemistry for lakes within the lakeshed, stream flow measurements and chemistry, and rain sampling events (stormwater). Sampling locations are provided in Table 8, a map of the locations is in Figure 6, and a color coded key with sampling frequency is below in Table 9 and 10. Water monitoring in the project involved measuring the chemical and physical water quality properties of three significant lakes, one significant stream, and two locations on Serpent Lake. SLA volunteers took grab samples on Peterson creek outlet from April to October during the summer of 2011 and summer 2012. SLA volunteers and SWCD personnel took two-meter water column samples on two sites on Serpent Lake from May to September two times per month. The lake profiling included depth profile vs. temperature, dissolved oxygen, pH and conductivity. In addition, SLA volunteers and the SWCD used a Van Dorn to take soluble reactive phosphorus samples close to the bottom of the lake on Serpent (18-0090) site 202 and 203. The MPCA was responsible for all physical stream flow measurements and provided the stream flow files to EOR. An EOR sub-contractor assembled the flow data along with the water chemistry data needed to run the BATHTUB Model. EOR used a segmented BATHTUB model for water and nutrient balance. The MPCA Brainerd office reviewed the BATHTUB modeling work.

Table 8. Monitoring sites

Site Name Code Station ID Site Name Code Station ID Serpent Lake 18-0090-00 Site 203 Serpent Creek S004-302

Serpent Lake 18-0090-00 Site 202 Peterson Creek S006-784

Unnamed Cranberry 18-0433-00 Site 201

City of Crosby Park S006-790

Unnamed/Peterson 18-0504-00 Site 201

City of Crosby stormwater culvert SS00014

Cascade 18-0061-00-Site 201 Unnamed Cranberry inlet S006-786

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Figure 6. Map of sampling locations

Table 9. Key to monitoring map

Key Type of Monitoring Frequency Parameters Rain Sampling Events

(stormwater) 5 times per year 1” or greater rain event

TSS,TSVS, SRP, TP

Flow Measurements & Chemistry

Daily 2 times per month April-October

TSS-April & Oct Only TSVS, N +N, TNK, TP, SRP,

Serpent Lake Profiling and Chemistry

2 times per month May-September

SRP, TP, Chl-a, Secchi, DO, Cond, pH, Temp.

Lake chemistry for lakes within the Lakeshed

1 sample per month May to September

Secchi, TP, Chl-A

5.1.3 Water quality monitoring quantitative goals

Serpent Lake (18-0090) Site 201 contained seven years of data for phosphorus, chlorophyll-a, and transparency readings (May-September). The CWP program allowed for a better assessment of current water quality trends. Data collected in 2011 and 2012 helped to create the implementation plan. An implementation plan will be part of the final reporting and incorporates the best recommendations based upon the modeling.

5.2 Watershed assessment To view Mississippi Brainerd Watershed Assessment visit link below: http://www.mn.nrcs.usda.gov/technical/rwa/Assessments/reports/elk_nokasippi.pdf. In addition, Watershed Assessment maps are located on the DNR website: http://www.dnr.state.mn.us/watershed_tool/index.html.

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General watershed assessment information involving land use is in Section 3.1.1 Project Area and Error! Reference source not found..

5.3 Quality control/quality assurance (field, laboratory, and office) Local volunteers were trained in quality assurance/quality control, and performed stream and lake water sampling, sample preparation, data collection/organization and shipping to RMB Laboratories Detroit Lakes (Cert # 027-005-336) via a SPEEDEE delivery service. RMB Laboratories completed chemical analysis of stream samples identified in program Section 3, Element 3 (American Fact Finder)and lake total phosphorus samples. RMB Laboratories furnished sample containers, labels, preservatives, coolers, chain-of-custody forms, and supplies. The stream samples were collected by a simple plastic bucket and poured into sample bottles. All collected data were transferred to Excel spread sheets, verified for accuracy and forwarded to EQuiS or modelers as appropriate. QA/QC procedures for RMB Laboratories were furnished upon request.

5.4 Lakeshed modeling techniques The Crow Wing SWCD provided monitoring data to EOR, including stream discharge at Peterson Creek and at the Serpent Creek site S004-302, stream inlets; and stormsewer discharge water quality data, and in-lake water quality data. Annual phosphorus loading to the lake from the monitored subwatersheds was estimated from the monitoring data, using a FLUX model. Phosphorus loading from the unmonitored subwatersheds was estimated by applying the calculated loading rates from the monitored subwatersheds. An in-lake response model was developed using the Bathtub model. The model was calibrated to the monitoring data collected for this project (2011 and 2012). The model was used to predict the response of Serpent Lake’s in-lake water quality if subjected to increases and decreases in phosphorus loading to the lake, and to determine the phosphorus load reductions needed for the lake to meet the water quality goals. These load reductions are the target load reductions for the implementation plan. The projects modeling goals are the following:

1. Compile collected data from the Peterson Creek automotive flow meter and Serpent Creek Outlet staff gauge measurements. See Figure 6. and Table 9.

2. Gather additional data about the lakes in the lakeshed and Serpent Lake including: landuse, well head protection areas, feedlot locations, population characteristics, landownership, and precipitation data.

3. Utilize the current collected data as well as any pertinent existing data, build the lake model scenario within BATHTUB model.

4. Following model development, an effort would be made to look at the effects of water quality changes on Serpent Lake.

5. Complete FLUX and BATHTUB models. Flux model will use Peterson Creek flow rates and water quality sample data to quantify the input nutrients to the Serpent Lake.

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6.0 Results

6.1 Description of project area

6.1.1 Existing land use

Figure 7. Land Cover Classification

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6.1.2 Soils

Higher infiltrating soils include the HSG B Rosholt and Chetek soils covering approximately 25% of the watershed and are generally located in Serpent Lake’s immediate watershed. The predominant coverage of less infiltrating HSG C or D soils is located in much of the remaining (75%) upland areas (LThia, Purdue University SWAT modeling summary). Hence, land areas closest to the lake will have greater potential to treat runoff via infiltration and filtration if treatment practices are properly designed, built and operated. This potential should be considered in future lake and watershed management programs and for this purpose, local units of government should examine the Minimal Impact Design Standards (MIDS) treatment practices (MPCA, 2012).

6.1.3 Population characteristics

According to the 2010 US Census Data, the population of Serpent Lake area is 5,358 this includes respectively, City of Deerwood 532, City of Crosby 2386, Irondale Township 1134, and Deerwood Township 1306. Median Age ranged from 39.7 to 52.3 ( 2010 Census Data).

6.1.4 Lake development, property value and economic summary

Based off CWC 2013 Serpent Lakeshed Parcel Datta, Serpent Lake is comprised of 417 parcels. Furthermore, data indicates Serpent Lake contains 198 homes built from 1887-2010 with a median age of about 36 years. Of these dwellings, 56% (110 homes) were listed as ‘Homestead’ and considered for the purposes of this assessment as occupied year-round with the remainder of the dwellings (87) considered seasonal. The average number of people per dwelling was assumed to be 2.3 capitas/year.

The ‘Estimated Fair Market Value’ for all properties associated with Serpent Lake was $127,787,300 with a total ‘Current Property Tax’ of $1,071,529. Recent economic survey information from Lac Courte Oreilles near Hayward, WI (Wilson, 2010) indicates that the average lake home spends approximately $10,000 to $15,000 per year on local services (groceries, electricians/plumbers/landscaping (trades), restaurants, building supplies, boats/docks/lake recreation industries, utilities, spirits etc.) At this level of average expenditure, Serpent Lake residents may spend about $2.0 million to $3.0 million (with no local multiplier applied) in the regional economy.

6.1.5 Community water supplies

The City Deerwood municipal wells are located within the Serpent Lake Lakeshed. Wellhead protection areas are adjacent to unnamed cranberry. See Fig. 8 below:

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Figure 8. Deerwood Drinking Water Supply Management Area

6.1.6 Point Sources of pollution

(1) Wastewater and feedlots in the watershed

There are no operating wastewater facilities that discharge to Serpent Lake. Deerwood constructed an activated sludge wastewater facility in 1964 that discharged to unnamed Cranberry Lake (MPCA, 1971) and thus into Serpent Lake. According to the City of Deerwood, the Serpent Lake Sanitary Sewer opened in 1986 or 1987 and closed the wastewater facility that discharged into unnamed Cranberry Lake at that time.

6.2 Project data and information

6.2.1 Agricultural watershed assessment

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Figure 9. Permitted feedlots in the Serpent Lake Watershed

6.2.2 Urban watershed assessment

The University of Minnesota Land Department GIS Mapping (2000) identifies Serpent Lakeshed as having one of highest ratios of urban land use and one of highest ratios of impervious surface to the lakeshed area compared to 415 other lakes in CWC. Furthermore, the Serpent Lake Lakeshed has no county tax forfeited, county, state or federal land within the lakeshed to protect the lakes and rivers from development pressures. This creates a greater need for protection strategies for Serpent Lake. Below is

a map and table of land use for the lakeshed from the year 2000 (Error! Reference source not found. and Table 1).

Table 10 Land use Serpent Lakeshed 1990 to 2000

Land Cover Acres Percent

Agriculture 113 3.41

Forest 959 28.92

Grass/Shrub/Wetland 744 22.44

Water 1,134 34.2

Urban 366 11.04

Impervious Intensity %

0 2,982 89.9

1-10 60 1.81

11-25 81 2.44

26-40 76 2.29

41-60 60 1.81

61-80 27 0.81

81-100 30 0.9

Total Area 3,316

Total Impervious Area (Percent Impervious Area Includes Water Area)

119 5.45

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Figure 10. 2000 impervious cover of the Serpent Lakeshed

6.2.3 Regional runoff and precipitation

The general Serpent Lake area has an annual average temperature of about 40 degrees with peak monthly mean temperatures reached in June through August and a growing season of about 90 days ( Table 11). There have been typically about 7 days a year exceeding 90 degrees F and 91 days with less than 32 degrees F.

Table 11. 1980-2012 Data Summary (from NOAA, 2012)

Over the past 10 years, the rainfall has averaged about 28.5 inches (720 mm), with considerably year-to-year variability ranging from 24.6 to 37.4 inches. The latter value was measured in 2012 and reflects over 7.7 inches of rain from the Duluth ‘Superstorm’ of June 17-21, 2012. Considerable variation in rainfall during the warm season (May–September) has been observed over the past 10 years with amounts varying from 11 inches (2006) to 28.4 inches (2012). Evaporation averages about 34 inches (~863 mm) per year. The recently released National Oceanic and Atmospheric Administration (NOAA) Atlas 14 rainfall intensity and duration report indicates that the 2-year storm has increased about 8% to 2.7 inches per 24 hours with the 50 and 100 year 24 hour storms increasing about 10% and 15%, respectively to 5.5 inches and 6.3 inches.

Element JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC ANN

Max °F 18.5 26.0 37.5 54.0 68.6 76.5 81.0 78.8 68.8 56.2 37.4 23.3 52.2

Min °F -7.5 -1.0 13.6 29.3 42.3 51.4 56.2 53.4 42.4 31.4 17.7 1.9 27.6

Mean °F 5.5 12.5 25.6 41.7 55.5 64.0 68.6 66.1 55.6 43.8 27.6 12.6 39.9

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Table 12. 2002-2012 Warm Season and Annual Precipitation for Riverton, MN (MDNR Site 216972)

From Minnesota Climatology Working Group, Wetland Delineation from Gridded Database.

Year

WARM (May-Sept)

ANNUAL

(inches) (inches) (m)

2012 28.38 37.43 0.95

2011 17.83 24.24 0.62

2010 20.25 28.63 0.73

2009 14.61 29.56 0.75

2008 16.00 27.80 0.71

2007 15.80 30.05 0.76

2006 11.07 18.16 0.46

2005 19.49 33.06 0.84

2004 17.22 26.34 0.67

2003 18.52 24.57 0.62

2002 24.45 33.25 0.84

Average 18.51 28.46 0.72

Total rainfall as measured at Riverton (Site 216972) totaled 37.43 inches in 2012, with 21 storms with over 0.5 inches and 11 storms exceeding 1.0 inches of rain per day. Most of these larger storms occurred during the growing season (May – September) as shown in Figure 11 below, providing reoccurring pulses of runoff to the lake during the growing season. Of particular note is the June 2012 ‘Superstorm’ that struck the northern areas of Minnesota causing massive flooding, erosion, and property damage across north-eastern Minnesota with more than 7.7 inches being monitored June 17-21, 2012 in Riverton, MN. This storm is of particular note as it will be referenced in discussions below pertaining to monitored runoff, lake level and lake water quality changes.

Figure 11. Serpent Lake (Riverton) Rainfall (2012)

(1) Climate Change Monitored changes in our climate over the past 30 years have been documented and include:

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1. More intense storms with the distribution of storms shifting to later in the summer; 2. Warmer temperatures and longer growing seasons; 3. Longer periods without ice cover; and 4. Wetter winters/springs/falls with summer dry periods (NOAA, 2013). Minnesota was noted in 2012 to have the third most rapidly increasing temperature in the country. There is a growing pattern observed with about 50% of the annual rainfall occurring in 10 or less days per year (NOAA, 2013). These patterns are not predicted to improve and thus, could have substantial effects on water resources.

6.2.4 Aquifer assessment

According into CWC Geological Survey Serpent Lake area contains buried sand aquifer associated with Brainerd assemblage South. The depth to the surficial aquifer varies from 25-50 on the North East side of Serpent to 0-25 on the south side of serpent.

6.3 Description of the water(s) of concern

6.3.1 Morphometric data

(1) Lake morphometric characteristics The morphometric characteristics for watershed lakes were determined from MDNR lake maps. Individual lake depth contour areas were determined by subtracting island/shoal areas. Volumes were calculated using the volume formula for the frustum of a circular cone: V = 1/3 × H (A1 + A2 + SQRT (A1 × A2)), where H is the depth, A1 is the bottom area, and A2 is the top area. Lake volumes were determined by contour area and summed. All summary morphometric estimates are listed in Table 13.

Table 13. Serpent Lake Watershed Summary Morphometric Characteristics*

*Calculated values from MDNR lake contour maps except no map for Rice Lake - values estimated.

Lake Surface Area Lake Volume Mean Depth Max Depth

Littoral Percent

acres km2 acre-feet hm

3 feet m feet m %

Serpent 1,103.1 4.47 29,400.5 36.3 26.7 8.1 65.0 19.8 31%

Agate 187.6 0.76 2,894.8 3.6 15.4 4.7 25.0 7.6 42%

Cascade 44.1 0.18 321.7 0.4 7.3 2.2 24.0 7.3 84%

Cranberry 15 0.06 45 0.06 ~3 0.9 -- -- 100%

Reno 167.5 0.68 705.7 0.9 4.2 1.3 9.0 2.7 100%

Rice 158 0.64 ~474 0.6 ~3 0.9 6.5 2.0 100%

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6.3.2 Monitoring stations and sample inventory by tributary, storm

Figure 12. Serpent Lake and Watershed Monitoring Network

6.3.1 In-lake samplings

Monitoring Locations 2011-2012 Lake and stream monitoring for this project was conducted at sites depicted in Figure 5 as outlined in Section 3.4.2

6.3.2 Long-term monitored total phosphorus, Chlorophyll-a and Secchi Transparency

Greenish colored water and a Secchi transparency of about 1.9 m was noted in 1949, as cited by MPCA (1971). More recent long-term volunteer Secchi monitoring data for Serpent Lake are plotted in Figure 6 shows higher transparencies in the late 1970’s and 1980’s averaging about 6.0 m (19.7 feet) with six total phosphorus values for that period averaging an anomalous high value of 40 ppb (see Figure 14). There also were no phosphorus data available from 1982 to 2001. Over the time period of 2002-2012, average summer transparency and total phosphorus values were 4.4 m (14.4 feet) and 13 ppb, respectively. The snapshot data from 1977-1981 versus 2001-2012 data records for Secchi transparency and total phosphorus indicate a statistically significant decline in transparency (CWC, 2011) along with a reduction in lake total phosphorus values at site 201. The 1977-1981 occurrences of relatively high total

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phosphorus concentrations coincidentally with high Secchi transparencies is unusual and cannot be explained from available data. Higher average summer total phosphorus concentrations were noted during summers of 2006-2008, that tended to be drier. Concurrently monitored average summer chlorophyll-a values typically have varied from 4 to 6 ppb (Figure 13) which are greater than anticipated based upon typical lake phosphorus-chlorophyll-a relationships.

Figure 13 Secchi Transparency Long-term Trends

Figure 14 Total Phosphorus Long-term Trends

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Figure 15 Chlorophyll-a Long-term Trends

6.3.3 2012 Total Phosphorus, Chlorophyll-a and Secchi Transparency The progression of total phosphorus, chlorophyll-a and Secchi transparency over the 2012 monitoring season is depicted in Figure 17, Figure 16, and Error! Reference source not found.. Figure 17 shows a general increase in lake total phosphorus over the growing season from the spring overturn (mixed waters with generally the same temperatures). Of particular note is the increase in lake phosphorus following the June 17-20, 2012 ‘Superstorm’. Serpent Lake total phosphorus increased from about 12 to 17 µg/L indicating that the lake is responsive to mixing and/or tributary inflows. This will be discussed more in detail later.

Concurrently monitored average summer orthophosphorus values comprised about 43% of average total phosphorus concentrations in 2011-2012, with in-lake concentrations generally peaking following storm events. This indicated relatively steady and significant external and/or internal orthophosphorus source(s) to Serpent Lake. Orthophosphorus is typically immediately available for algal growth, and therefore a priority for future watershed management actions. Elevated Serpent Lake chlorophyll-a responses were similarly greater than typical Northern Lakes and Forests (NLF) ecoregion phosphorus: chlorophyll-a relationships noted in Heiskary and Wilson (2008). A concurrent reduction in Secchi transparency was also noted (due to the increased chlorophyll-a) with a shift away from typical NLF phosphorus: chlorophyll-a: Secchi relationships. BATHTUB model assessments in this study incorporated these effects into the response variables.

Chlorophyll-a shows a delayed increase following increases in lake total phosphorus by about 2-3 weeks as concentrations increased from less than 5 ppb in April-May to summertime concentrations of 5-12 ppb (Figure 16). Lake algal concentrations typically take more than 15 days to respond to the increase in phosphorus such as noted in Serpent Lake. Lake transparency values peaked at over 6.4 m (~21 feet) on May 6, 2012 and steadily declined over the growing season to about 2.5 m (~8 feet) by September, 2012 (Error! Reference source not found.). The steady decline of transparency suggests a relatively steady input of phosphorus into the lake’s surface waters.

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Figure 16. Seasonal Trends in Total and Ortho Phosphorus (2012)

Figure 17. Seasonal Trends in Chlorophyll-a (2012)

Figure 18. Seasonal Trends in Secchi Transparency (2012)

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6.3.4 Dissolved oxygen and temperature diagrams

Volunteer monitoring of temperature and dissolved oxygen concentrations by depth were conducted at two lake stations (-202 and -203 in Figure 5) over the two open-water seasons of the study (2011-2012). Dissolved oxygen and temperature data from the deeper site 203 were selected from the spring, summer, late summer and early fall. Figures 19 to 22 show the 2012 sequence of seasonal effects. The cool/cold waters of early spring and late fall are typically well-mixed and show little difference in oxygen and temperatures from top to bottom. This is called isothermal and occurs at turn-over with the lake is mixing from top to bottom. As temperatures warm, so do the lake waters, creating temperature layers with warmer (lighter) waters on the top separated from the cold bottom waters by a thermocline or zone of rapid transition of temperature. The lake displays a clinograde pattern with very low or no oxygen below the ~ 7 m depth (23 feet) during stratified conditions. Powerful summer storms can disrupt the thermal layers and cause mixing to substantial depths (e.g. 40 feet witnessed in Jessie Lake monitoring; Wang et al, 2004) and cause mixing of phosphorus enriched anoxic bottom waters that may generate algal blooms. With increasingly intense summer storms, this may periodically occur and should be tracked over time. Serpent Lake is considered a dimictic lake based on criteria of Heiskary and Wilson (2005) and monitored 2011-2012 temperature/ oxygen dynamics, meaning it mixes in the spring and fall.

Oxygen was quickly consumed in the bottom (unmixed with surface storms) waters by the end of June, 2012 such that the bottom 5 to 7 feet of water was essentially without oxygen. The cold bottom waters (hypolimnion) continued to lose oxygen affecting the thermocline, such that very low oxygen (e.g. less than 5.0 mg/L) was noted below about 7 m (23 feet) from mid-to-late July until about mid-September.

Figure 19. Temperature and Dissolved Oxygen by depth at Site 203 (May 7, 2012)

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Figure 20. Temperature and Dissolved Oxygen by depth at Site 203 (June 26, 2012)

Figure 21. Temperature and Dissolved Oxygen by depth at Site 203 (August 29, 2012)

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Figure 22. Temperature and Dissolved Oxygen by depth at Site 203 (September 20, 2012)

6.3.5 Secchi transparency plots

Figure 23. Secchi Transparency Long-term Trends

6.3.6 Map of monitoring network: See Figure 12

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6.3.7 Water balances for the study period

Table 14. Monitoring station average TP, OP, and TKN (2012)

Station Identification

Number Average TP

(ppb) Average OP

(ppb) Average TKN

(ppb)

Peterson Creek S006-784 26 7 471

Cranberry Outlet S006-786 173 52 NA

Crosby Park S006-790 134 57 NA

Crosby Stormwater SS00014 122 33 NA

Table 15. Summary of Serpent Lake Runoff Used to Construct 2012 Water Budget

Subwatershed Area (acres / km

2)

Average Runoff (m/year)

Flow-weighted Mean TP (ppb) / Monitored average orthoP (ppb)

Agate Lake 753 / 3.0 Little discharge reported 19

Cascade Lake 193 / 0.8 Little discharge reported 14

Cranberry Discharge 392 / 1.6 0.17 173 / 52

Deerwood Stormwater ~310 / 2.5 0.2 128

Crosby Stormwater 240 / 0.9 0.2 128 / 57

Rice Lake through Peterson Creek

1,287 / 5.2 0.7 20

Reno Lake 1,026 / 4.2 No discharge reported 17

Serpent Lake Immediate Drainage (less lake)

1,628 / 6.6 0.8 40

Total Watershed (including lakes)

6,381 / 25.8 2.8 15

6.4 Peterson Creek Peterson Creek flows (H10090001 in Figure 5) were gauged by MPCA Brainerd staff, from June 10, 2011 through November 14, 2012. Measured flows were coupled with volunteer sampled total phosphorus and total Kjeldahl nitrogen concentrations to determine loads using the USACE FLUX software (Walker, 1996). These loads are summarized in Table 17. Peterson Creek runoff was quite responsive to rainfall (Figure 24). Measured flows increased from less than 1 cubic foot per second (cfs) to over 6 cfs in response to the ‘Superstorm’ of June, 2012 with about 7.7 inches of rain falling in the area from June 17-21, 2012. Correspondingly, Serpent Lake levels increased about 1 foot and slowly dropped over the next three months ( Figure 25).

Table 16. Peterson Creek flow and load summary

Parameter 2011 2012

Monitored volumes (hm3) 0.35 (6/10/11-11/6/11) 0.68 (3/2/12-11/14/12)

Monitored volumes (acre-feet) 8.2 15.6

Flow-Weighted Mean TP (ppb / CVmean)

20 ppb / 0.06

Flow-Weighted Mean Total Kjeldhahl N (ppb / CVmean)

486 ppb / 0.04

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Figure 24. 2011-2012 Peterson Creek Flows Monitored by the MPCA and daily rainfall totals

Note: Flows were not able to be collected after freeze-up in November, 2011 until the spring runoff of March, 2012

Figure 25. Serpent Lake Levels, Volunteer Monitoring (2012)

No flows

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FLUX estimated runoff and flow-weighted mean concentrations for Peterson Creek was based on all available total phosphorus and total Kjeldahl nitrogen grab samples and flows. 2012 annual flow volumes were used to construct the 2012 water inflow-outflow summaries as this time period had the most complete flow monitoring record. Average total phosphorus 2011-2012 values from monitored stations (Peterson Creek, Cranberry Lake discharge, Crosby stormwater, Deerwood stormwater, and Serpent Lake discharge based on average lake concentrations) were used along with estimated runoff for un-gauged flow sites. Average lake total phosphorus concentrations were also used to estimate average runoff from Agate and Reno Lake outlet values.

6.4.1 Flow-weighted mean concentrations of measured parameters by tributary Table 17. Peterson Creek flow and load summary

Parameter 2011 2012

Monitored volumes (hm3) 0.35 (6/10/11-11/6/11) 0.68 (3/2/12-11/14/12)

Monitored volumes (acre-feet) 8.2 15.6

Flow-Weighted Mean TP (ppb / CVmean)

20 ppb / 0.06

Flow-Weighted Mean Total Kjeldhahl N (ppb / CVmean)

486 ppb / 0.04

6.4.2 Nutrient balances

FLUX estimated runoff and flow-weighted mean concentrations for Peterson Creek was based on all available total phosphorus and total Kjeldahl nitrogen grab samples and flows. 2012 annual flow volumes were used to construct the 2012 water inflow-outflow summaries as this time period had the most complete flow monitoring record. Average total phosphorus 2011-2012 values from monitored stations (Peterson Creek, Cranberry Lake discharge, Crosby stormwater, Deerwood stormwater, and Serpent Lake discharge based on average lake concentrations) were used along with estimated runoff for un-gauged flow sites. Average lake total phosphorus concentrations were also used to estimate average runoff from Agate and Reno Lake outlet values.

Table 18. Monitoring station average TP, OP, and TKN (2012)

Station Identification

Number Average TP

(ppb) Average OP

(ppb) Average TKN

(ppb)

Peterson Creek S006-784 26 7 471

Cranberry Outlet S006-786 173 52 NA

Crosby Park S006-790 134 57 NA

Crosby Stormwater SS00014 122 33 NA

Table 19. Summary of Serpent Lake Runoff Used to Construct 2012 Water Budget

Subwatershed Area (acres / km

2)

Average Runoff (m/year)

Flow-weighted Mean TP (ppb) / Monitored average orthoP (ppb)

Agate Lake 753 / 3.0 Little discharge reported 19

Cascade Lake 193 / 0.8 Little discharge reported 14

Cranberry Discharge 392 / 1.6 0.17 173 / 52

Deerwood Stormwater ~310 / 2.5 0.2 128

Crosby Stormwater 240 / 0.9 0.2 128 / 57

Rice Lake through Peterson Creek

1,287 / 5.2 0.7 20

Reno Lake 1,026 / 4.2 No discharge reported 17

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Serpent Lake Immediate Drainage (less lake)

1,628 / 6.6 0.8 40

Total Watershed (including lakes)

6,381 / 25.8 2.8 15

The BATHTUB model was used to formulate water and nutrient balances and to predict in-lake effects resulting from alternative watershed management options based on changes to water and nutrient loading rates. BATHTUB employs a network of empirical models and was developed by William Walker (Walker, 1996) for the US Army Corps of Engineers, Waterways Experiment Station (USACE-WES), Vicksburg, Mississippi. Detailed documentation of the model origins, structures and limitations can be found in Walker (1985 and 1996). Flow-weighted mean concentrations and volumes are summarized in Table 20. The chlorophyll-a model was calibrated to reflect the increased orthophosphorus inputs to the lake that result in increased algal response and dampened Secchi transparency estimates. The model was calibrated to 2012 measured values for total phosphorus, chlorophyll-a and Secchi. A summary of inputs and model outputs is included in the appendix. The predicted lake water residence time was quite long (10.4 years) and is another indication of sediment ‘memory’ or potential for internal loading of phosphorus.

Table 20. Phosphorus Loading Estimated to Serpent Lake 2012

Subwatershed Load

kg/yr % total

Agate Lake WS1 0.9 0.4%

Cascade Lake Ws 0.3 0.2%

Cranberry Lake Ws 26.0 12.3%

Deerwood Stormwater 25.6 12.1%

Reno Lake 0.2 0.1%

Peterson Creek 13.6 6.4%

Crosby Stormwater 24.3 11.5%

SSTS 21.0 9.9%

Shoreline Runoff 24.0 11.4%

Rainfall 67.0 31.7%

Outlet - Discharge 44.4 -21.2

Groundwater 8.4 4.0%

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Table 21. BATHTUB model water and mass balances

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7.0 Discussion

7.1 Assessment of the project's resource water quality

Serpent Lake is extremely sensitive to phosphorus loading from external watershed and in-lake recycling (internal loading) sources and particularly of orthophosphorus sources. In this regard, these rehabilitative measures were modeled to collectively achieve a 10 ppb average summer total phosphorus based on the 2012 flow data:

7.2 Assessment of pollutant loads

The BATHTUB model was used to formulate water and nutrient balances and to predict in-lake effects resulting from alternative watershed management options based on changes to water and nutrient loading rates. BATHTUB employs a network of empirical models and was developed by William Walker (Walker, 1996) for the US Army Corps of Engineers, Waterways Experiment Station (USACE-WES), Vicksburg, Mississippi. Detailed documentation of the model origins, structures and limitations can be found in Walker (1985 and 1996). Flow-weighted mean concentrations and volumes are summarized in Table 22. The chlorophyll-a model was calibrated to reflect the increased orthophosphorus inputs to the lake that result in increased algal response and dampened Secchi transparency estimates. The model was calibrated to 2012 measured values for total phosphorus, chlorophyll-a and Secchi. A summary of inputs and model outputs is included in the appendix. The predicted lake water residence time was quite long (10.4 years) and is another indication of sediment ‘memory’ or potential for internal loading of phosphorus.

Table 22. Phosphorus Loading Estimated to Serpent Lake 2012

Subwatershed Load

kg/yr % total

Agate Lake WS1 0.9 0.4%

Cascade Lake Ws 0.3 0.2%

Cranberry Lake Ws 26.0 12.3%

Deerwood Stormwater 25.6 12.1%

Reno Lake 0.2 0.1%

Peterson Creek 13.6 6.4%

Crosby Stormwater 24.3 11.5%

SSTS 21.0 9.9%

Shoreline Runoff 24.0 11.4%

Rainfall 67.0 31.7%

Outlet - Discharge 44.4 -21.2

Groundwater 8.4 4.0%

An in-lake phosphorus concentration goal defined relative to the ecoregion phosphorus criteria.

7.3 Resource water quality goals

To maintain or improve the water quality of Serpent Lake, phosphorus (and in particular orthophosphorus) needs to be reduced from the following sources. We estimated that these reductions will reduce average summer total phosphorus to about 10 ppb.

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1. Investigate chemical treatment of Cranberry Lake to reduce average phosphorus concentrations to background (e.g. from 173 to 20 ppb). This was predicted to decrease average P loads by 23kg/ year resulting in an estimated average summer total phosphorus concentration reduction in Serpent Lake of about 1 ppb.

2. Employ new stormwater performance goals as described by the Minimal Impact Design Standards (MIDS) for stormwater: treat the first 1.1 inch of runoff from impervious surfaces on-site for new developments. These practices have been shown to decrease total phosphorus by about 80% +.

3. Closely review compliance to SSTS standards and upgrade old systems as the average age of homes along the lake is about 37 years and some of the systems may be out of compliance.

4. Fully buffer the lakeshore with infiltration type practices such as rain gardens and uncompacted native perennial vegetation.

7.4 Target reductions of pollutants needed to meet water quality goals 1. Reduce Cranberry Lake total phosphorus loading from 26 kg/year to 3 kg/year P or from average

concentrations of 173 ppb to 20 ppb; 2. Reduce Crosby and Deerwood Stormwater total phosphorus loading by 50% to about 25 kg

P/year; 3. Reduce subsurface sewage treatment systems by 50% to about 10 kg P/year.

Increased phosphorus loads can be expected from these five general sources unless additional management steps are undertaken:

1. Subsurface sewage treatment systems

The estimated contributions from septic systems were ~20 kg P/year with a 95% attenuation rate for 198 lakeshore homes and seasonal residences. Failing systems or overloaded systems could quickly generate an additional 40 to 80 kg P/year (88 to 176 pounds P/year),

2. New and existing urban stormwater Higher intensity/density lakeshore development and continued development within the Crosby and Deerwood municipal areas can be expected to increase phosphorus loading to the lake unless stormwater volume control approaches are employed to infiltrate stormwater (by use for example of rain gardens) and minimizing new impervious surfaces.

3. Internal loading There is evidence that there is internal P being generated from lake sediments. Lake modeling described herein did not explicitly add additional internal loading. It is strongly suggested that the lake’s bottom waters be monitored for total iron with a general expectation that if total iron is about three times greater than total phosphorus, then internal loading may not be excessive. With low concentrations of iron, future internal loading rates may exceed lake assimilative capacities and thereby cause rapid increases in lake phosphorus concentrations. If the lake were to experience an increase in internal loading of 0.25 mg/m2/day (as modeled in BATHTUB), then an additional 408 kg P (about 900 pounds P) was estimated driving average summer total phosphorus values from 12 ppb to about 25 ppb.

4. Climate change The collective effects of climate change may increase the background loading of phosphorus from watershed sources. Likely sources of increased P loads may be due to dry/wet cycles causing increased wetland P losses, large storms generating shock loads as occurred from the ‘Superstorm’ of June 2012, and increased lake temperatures. Generally it is expected that the summers may tend to have less rainfall, with reduced lake levels a distinct possibility (National Climate Assessment and Development Advisory Committee, 2013).

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To maintain or improve the water quality of Serpent Lake, phosphorus (and in particular orthophosphorus) needs to be reduced from the following sources. We estimated that these reductions will reduce average summer total phosphorus to about 10 ppb.

8.0 Conclusions Future lake sampling should continue based on Secchi Transparency and augmented with surface samples of total phosphorus and chlorophyll-a. It is strongly recommended that bottom waters be sampled 3-5 times a summer for total iron concentrations as a gauge of internal loading sensitivity.

Figure 26. Serpent Lake BATHTUB loading general sensitivity to increases or decreases in total phosphorus loads.

8.1.1 Future Management Goal Recommendations:

Suggested Serpent Lake TP Goal = 10 ppb ±2

0

5

10

15

20

25

0 100 200 300 400 500

TO

TA

L P

M

G/M

3

Total P Load (kg/yr)Means +/- 1 Std Error

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9.0 References American Fact Finder. (n.d.). Retrieved June 28, 2013, from Community Facts: http://factfinder2.census.gov/faces/nav/jsf/pages/community_facts.xhtml Blann, K. L., J. L. Anderson, G. R. Sands and B. Vondracek. 2009. Effects of Agricultural Drainage on Aquatic

Ecosystems: A Review. Critical Reviews in Environmental Science and Technology 39: 909-1001.

Developing Nutrient Criteria.” 3rd Ed.” MPCA. St. Paul MN 150 pp.

Heiskary, S.A. and C.B. Wilson. 2005. “Minnesota Lake Water Quality Assessment Report:

National Oceanographic and Atmospheric Administration, 2013. Regional Climate Trend and Scnearios for the U.S. National Climate Assessment. Part 3. Climate of the Midwest U.S.

National Climate Assessment and Development Advisory Committee. 2013. Draft National Climate Assessment Report. Chapter 18 Midwest. Convening Lead Authors. Pryor, Sara C. and Donald Scavia. www.ncadac.globalchange.gov/...publicreviewdraft-chap18-midwest.pdf

Seaber, P.R., F.P. Kapinos, and G.L. Knapp. 1987. Hydrologic units maps: U.S. Geological Survey Water-Supply

Paper 2294, 63 p.

United States Department of Agriculture, Natural Resources Conservation Service. 2011. Land Resource Regions and Major Land Resource Areas of the United States, the Caribbean, and the Pacific Basin. U.S. Department of Agriculture Handbook 296.

Wilson, C.B. and W.W. Walker. 1989. Development of lake assessment methods based upon the aquatic ecoregion concept. Lake and Reserve. Manage. 5(2):11-22.

Wang, H., M. Hondzo, B. Stauffer and Bruce Wilson. 2004. Phosphorus Dynamics in Jessie Lake: Mass Flux Across the Sediment-Water Interface. Lake and Reservoir Management. 20(4):333-346.

Wilson, C.B. 2010. Lac Courte Oreilles Economic Survey and Assessment. Prepared for COLA, Hayward Wisconsin. 24 pp.

10.0 Distribution List

Table 23. Distribution List

No. of Copies Sent to

2 Chris Pence Director, Crow Wing County Environmental Services Land Services Building 322 Laurel Street, Suite 14 Brainerd, MN 56401

1 Bonnie Finnerty MPCA Pollution Control Specialist 7678 College Road, Ste. 105 Baxter, MN 56425

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1 City of Crosby 2 Second Street SW Crosby, MN 56441

1 Clark Marshall Project Coordinator, Serpent Lake Association Second Street SW Crosby, MN 56441

2 Patrick Conrad and Bruce Wilson Emmons & Olivier Resources (EOR) 651 Hale Ave N Oakdale, MN 55128