Lake Sarah is a 553-acre lake located approximately 24 miles west of Minneapolis in west central Hennepin County. The Lake Sarah watershed was dominated by woodlands, grasslands, and wetlands before initial European settlement of the Greenfield area in the 1850s. The onset of agriculture brought the removal of the hardwood forests and the draining of wetlands and small lakes in the watershed. Agriculture continues to dominate the landscape in the Lake Sarah watershed, though agricultural parcels are being subdivided to accommodate rural residential development on 2 to 40-acre lots.
Lake Sarah receives runoff from a 4, 454-acre mixed-use watershed which drains land from portions of five municipalities - Greenfield, Independence, Corcoran, Loretto, and Medina. Primary land uses are agriculture (23%), rural residential (22%), medium density residential (7%), wetland (21%), and commercial (3%). Approximately, 3% of the land in the watershed is dedicated to pasture and feedlots for horses and cattle. Most of the shoreline land is occupied by single family residential homes, but the shoreline also includes a horse farm, a cattle farm, wetland areas, and parkland. Property along the western shoreline of the lake is within the Lake Sarah Regional Park, operated by Three Rivers Park District.
In 2006, Lake Sarah was identified for impairment of aquatic recreation (swimming) and placed on the Minnesota Pollution Control Agency's (MPCA) 303(d) list of impaired waters. The impaired water designation was based on an exceedance of state water quality standards: total phosphorus (< 40 µg/L); Chlorophyll-a (< 14 µg/L); and secchi disc transparency (> 1.4 m). Assessment of average water quality conditions (TP = 101 µg/L, Chl-a = 42 µg/L, Secchi = 1.5 m), was based on over ten years of biweekly monitoring data.
Phosphorus in Lake Sarah originates from two primary sources - watershed runoff and in-lake nutrient cycling (i.e. internal loading). Runoff occurs from agricultural sources such as row and forage crops, animal feedlots, and pastures; low and medium residential development, commercial and industrial development, highway and road surfaces, and undeveloped areas such as forests and wetlands.
Internal loading in lakes refers to the re-cycling and re-suspension of in-lake phosphorus into the water column. There are two primary sources of internal loading in Lake Sarah - direct sediment release and curlyleaf pondweed senescence (i.e. die-off). Watershed runoff contributes approximately 38% of the total annual phosphorus load to the lake, and internal loading accounts for 59% of the total annual load. Atmospheric deposition accounts for only a small percentage (3%) of the total phosphorus loading to the lake.
The Lake Sarah TMDL indicates that to consistently meet the state's in-lake water quality standards under average annual precipitation conditions, nutrient loads from watershed and in-lake sources need to be reduced by 4,330 pounds of total phosphorus per year (79% of the existing combined internal and external phosphorus loads to the lake). Approximately 1,108 pounds per year of phosphorus reduction (about 26% of the overall load reduction target) will come from reductions in watershed loadings. The remaining 3,222 pounds per year of reduction in phosphorus loading (or 74% of the load reduction target) will come from control of internal loading in the form of curlyleaf pondweed control and reductions in sediment phosphorus release.
The Lake Sarah TMDL Implementation Plan provides guidance on the specific activities the stakeholders in the watershed plan to undertake to attain the reductions identified in the TMDL.
A detailed implementation strategy was developed through interpretation of the monitoring and modeling results and an ongoing public participation process. Twenty-five stakeholder meetings were held throughout the TMDL development process and the resulting implementation strategy highlights the need to comprehensively address both watershed and internal sources of phosphorus. The Implementation Plan was approved by the Minnesota Pollution Control Agency on September 16, 2011.
Reduction of the watershed load will be achieved by implementing a series of Best Management Practices (BMPs) related to row crop agriculture, feedlot and manure management, residential and commercial development and restoration of stream, wetland and shoreline habitat.
Reductions in internal load will be achieved through a combination of curlyleaf pondweed control and sediment phosphorus sequestration. Total costs for implementation efforts are anticipated to range between $1.22 million and $3.66 million for all in-lake and watershed restoration work. The implementation time frame for all measures is expected to be up to 10-15 years.
The Lake Sarah TMDL received EPA approval April 25, 2011. The last phase of the TMDL project was to create an Implementation Plan for MPCA review and approval. The Implementation Plan details how the Commission planned to meet the load reductions in the TMDL and includes estimated costs and timelines for sequencing.
Dance Hall Creek Subwatershed Assessment
Lake Sarah is a highly utilized and valued public resource in the Pioneer-Sarah creek Watershed. In 2011 the Pioneer Sarah Creek Watershed Management Commission, in partnership with the Minnesota Pollution Control Agency (MPCA) and Three Rivers Park District (TRPD), completed a Total Maximum Daily Load (TMDL) analysis to quantify the phosphorus reductions needed to meet state water quality standards for nutrients in Lake Sarah in accordance with the Clean Water Act. The study identified the Dance Hall Creek watershed as a "hot-spot" for contributing nutrients to Sarah Lake. Dance Hall Creek drains to Sarah Lake which drains via Sarah Creek to the Crow River.
In 2013 the Hennepin County Environmental Services Department (HCES) performed a stormwater retro-fit study for the Dance Hall Creek watershed within the City of Greenfield. The study was a partnership between the HCD, HCES, City of Greenfield, and Crow River Watershed Association. Data from the study will be utilized by the partners to seek Clean Water Legacy BMP funds.
Pioneer-Sarah Watershed Management Commission 3235 Fernbrook Lane N, Plymouth, MN 55447 Phone (763) 553-1144 Fax (763) 553-9326 Email firstname.lastname@example.org