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The purpose of the Blue Earth River Watershed study was to (1) characterize common pollutant levels in the Blue Earth River and selected tributaries; (2) create a Geographic Information System (GIS) for the Blue Earth River watershed to provide spatial natural resources data for each sampling sub watershed, that will serve as a tool for continued planning and management of natural resources in the watershed; and (3) determine the loading of the Blue Earth River to the Greater Blue Earth River Watershed and to the Minnesota River.

In 1992, the Minnesota River Assessment Project (MRAP) indicated that sediment is a pollutant of primary concern and recommended a 40 percent reduction in sediment loading. Consequently, the monitoring program and watershed assessment for the Blue Earth River Watershed, which occurred during 1996, focused on the concentration and loading of sediment, as total suspended solids (TSS). A Geographic Information System (GIS) was used to develop land use/land cover and physical data (hydrographic, soil, slope, updated land use, feedlots, monitoring sites, sub watersheds); derived layers were created to analyze the 16, 99, and 300 foot riparian zones, locate potentially restorable wetland areas, and to identify highly erodible areas. The Blue Earth River Watershed Team met during 1998 - 2000 to review watershed data, identify priority areas, and develop an implementation plan for improved water quality in the Blue Earth River Watershed.

The Blue Earth River Major Watershed is one of the twelve major watersheds of the Minnesota River Basin located in south central Minnesota with a total area of approximately 1,550 square miles or 992,034 acres. Of the 992,034 acres, 775,590 acres are located in Minnesota and 216,444 acres are located in Iowa. Physical and land use data were collected only for the Minnesota area of the watershed; however, land use data were normalized for the Iowa portion of the watershed. The Blue Earth River Watershed is a region of gently rolling prairie and glacial moraine with river valleys and ravines cut into the landscape. As the mainstem of the Blue Earth River flows north-northeast, it is joined by the Watonwan River at 16.3 river miles and by the Le Sueur River at 3.3 river miles from the Blue Earth RiverĘs confluence with the Minnesota River. The watersheds of the Blue Earth, Le Sueur and Watonwan rivers define a sub-basin of the Minnesota River Basin referred to as the Greater Blue Earth River Watershed.

The Blue Earth River Major Watershed drainage network is defined by the Blue Earth River and its major tributaries: the East Branch of Blue Earth River, the West Branch of Blue Earth River, the Middle Branch of the Blue Earth River, Elm Creek, and Center Creek. Other smaller streams, public and private drainage systems, lakes, and wetlands complete the drainage network. The total length of the stream network in Minnesota is 1,178 miles of which 414 miles are intermittent streams and 764 miles are perennial streams. Extensive artificial drainage made up of public and private ditch and tile systems facilitate the movement of water throughout the watershed. Pollutants such as nutrients, bacteria and sediment can be transported with the water. Approximately 86 percent of wetlands were lost through drainage. Remaining lakes and wetlands comprise about 2% of the watershed. Predominate land use within the watershed is agriculture, which includes cultivation and feedlot operations. Various land uses as well as areas prone to erosion (steep slopes, unprotected vertical stream banks) are sources of sediment observed in streams. Areas of concern were identified in the riparian zone of the mainstem of the Blue Earth River, Elm Creek, Lily Creek, Willow Creek and Center Creek.

The monitoring protocol used the designation of primary, secondary, and tertiary water monitoring sites. More resources (time and parameters) were used on the primary sites and secondary sites than on the tertiary sites. As a result, sediment measured as TSS and levels of turbidity were the only consistent pollutant parameters measured at all sites. These were practical limitations based on the scale and budget of the overall project. The flow and water quality monitoring of the watershed from April to November in 1996 provided concentration, load, and yield estimates of total suspended solids (TSS) and other selected parameters at two primary and four secondary monitoring sites. Concentration, load, and yield estimates of TSS and levels of turbidity were determined for 11 tertiary sites. Two sites, BT7 and BT8, were located to analyze water quality and flow data from the majority of the Iowa area. Data reported for the Blue Earth River at Mankato, site BP1, characterized the collective water quality and flow resulting from the Blue Earth, Le Sueur and Watonwan rivers; these data are discussed as part of the Greater Blue Earth River Watershed.

Data reported for the Blue Earth River near Good Thunder, site BP2, characterized the watershed before the addition of flow and pollutants from the Le Sueur and Watonwan rivers and is the basis for sub watershed comparisons. Monitoring of the watershed at BP2 estimates total discharge for the monitoring season at 274,954 acre feet. The TSS load of the Blue Earth River at BP2 was estimated at 98,630 tons or an average yield of 202 pounds per acre for the monitoring period. Loading of TSS was highest on the mainstem of Blue Earth River at two sites, although the yield of TSS as pounds per acre was highest at the lower reach of the Blue Earth River and at Elm Creek. Results from 8 of the 16 sub watersheds estimated individual watershed yields of TSS exceeding 150 pounds per acre. The phosphorus load of the Blue Earth River (BP2) was estimated at 130 tons of total phosphorus and 23 tons of ortho-phosphorus; the nitrate-nitrogen load was estimated at 2,752 tons. The phosphorus yield of the Blue Earth River (BP2) was estimated at 0.27 pounds per acre of total phosphorus and 0.05 pounds per acre of ortho-phosphorus; the nitrate-nitrogen yield was estimated at 5.63 pounds per acre.

The concentration data were compared to the ecoregion values (IQR) for least impacted areas in the Western Corn Belt Plains (WCBP) Ecoregion. The TSS, phosphorus, turbidity, nitrate-nitrogen and ammonia concentrations measured in 1996 exceeded, and in some cases significantly exceeded the water quality concentrations for minimally impacted streams in the same ecoregion. The water quality standard for coliform bacteria concentration is 200 cfu per 100 ml. Measured fecal coliform bacteria in the Blue Earth River Watershed exceeded this standard ranging from 5 to 12,040 cfu per 100 ml with highest counts found in the upper reach of the Blue Earth River.

The Le Sueur River, the Watonwan River and the Blue Earth River watersheds are collectively referred to as the Greater Blue Earth River Watershed; these watersheds were monitored concurrently during 1996. Data from the diagnostic study may be compared on the basis of percent distribution among the three watersheds at their primary sites, BP2, LP1, WP1, characterizing each watershedĘs flow and water quality prior to the confluence of the rivers. Data may also be compared using each of the watershedĘs primary sites, BP2, LP1, WP1, as a percent of the Blue Earth River site BP1, resulting in an estimate of each watershedĘs contribution of flow and load to BP1 and to the Minnesota River. An additional means of comparison for the three watersheds is to use normalized data. The yield of pollutants expressed as pounds per acre or tons per acre of watershed normalizes the data allowing the comparison among watersheds with varying area.

Site BP2 characterizes the Blue Earth River near Good Thunder before the addition of flow and pollutants from the Le Sueur and Watonwan rivers; LP1 is near the outlet of the Le Sueur River, and WP1 is near the outlet of the Watonwan River. When comparing the three watersheds, the percent distribution (Table 1) indicates that the Le Sueur and the Blue Earth contribute the majority of the TSS load and TP load. These data suggest that the Le Sueur River Watershed is the most significant source of sediment of the three watersheds, considering the contribution of TSS loading from the Le Sueur is considerably more than its proportion of flow, and that the Le Sueur generates approximately 256 pounds per acre of TSS. Although the Le Sueur generates the highest yield of TSS, the Watonwan generates the highest yield of TP, suggesting the impact of point source discharges of TP from the Watonwan. The Blue Earth generates the highest load of N-NO3, however the Watonwan generates the highest yield of N-NO3, followed by the Blue Earth, and then the Le Sueur. Historical studies of the Minnesota River Basin report that these three watersheds cumulatively contribute the majority of N-NO3 to the Minnesota River.

Table 1. Percent Distribution of Total Watershed Area, Flow and Pollutant Load

Site BP2 of Blue Earth River and the discharge from the Watonwan River are upstream of the Rapidan Reservoir; the Le Sueur River enters the Blue Earth River downstream from the reservoir. The reservoir is part of the small watershed, subBP1 (35,562 acres); subBP1 is the area located between the primary sites ( BP2, LP1, WP1) and the Blue Earth River at Mankato, site BP1as shown in Figure 1. The flow summary for the 1996 monitoring season, showed the total discharge of BP2, LP1, and WP1 was less than the discharge at BP1, indicating a gain of 6% flow from subBP1.

Figure 1. Location of subBP1 watershed.

The calculated percent contribution from the Blue Earth, Le Sueur, and Watonwan watersheds as shown in Table 2, may not equal 100 percent due to the loss or gain of pollutants before BP1. The results from the 1996 monitoring season indicate significant load and yield contributed from the Blue Earth, Le Sueur and Watonwan rivers; however, a reduction of sediment load occurred prior to the delivery of sediment to the Minnesota River. Significant reductions of pollutants occurred in subBP1, with the exception of nitrate-nitrogen, which increased in loading as well as in yield. The 1996 loading and yield data indicate that the Greater Blue Earth River Watershed generates significant loading of TSS to the Minnesota River Basin consistent with historic data.

Table 2. Percent Distribution of Watershed Area, Flow and
              Pollutant Load to the Minnesota River

In addition to the monitoring results, the Blue Earth River Watershed Team used land use and physical watershed characteristics to identify areas of concern. The load, yield, and concentration of TSS for the primary, secondary and tertiary sites were of crucial importance in identifying priority areas for implementation. The watershed team developed the Implementation Plan following an organized methodology. Priority management areas and management strategies were selected to improve water quality, considering both nonpoint source and point source pollution. Upon completion of implementation planning, the consensus was to target implementation efforts within the following priority management areas: the Blue Earth River (BS2), Lily Creek (BT1), and Center Creek (BT4) based upon land use, physical and chemical data collected as well as size and locations of the sub watershed. Elm Creek (BS1), Willow Creek (BT5), and the Blue Earth River (BP2) watersheds were also identified as priority management areas. Focused-Geographic Goals were developed to target initial efforts in priority management areas over the next 3 to 6 years. Watershed-Wide Implementation Strategies were developed, providing long-term, watershed-wide strategies to continue watershed efforts over 10-20 years. The anticipated time frame needed for coordinated implementation in the Blue Earth River Watershed is projected over the next 6 to 10 years and into the next 10 to 20 years.

Priority management areas selected for immediate implementation over the next 3-6 years were Lily Creek (BT1) and Center Creek (BT4), sponsored by Martin County. The direction of the implementation plan is to focus initial efforts in the priority management areas. Additional watershed management activities, conservation efforts, monitoring and the promotion of existing programs are the broad based components of the Blue Earth River Watershed Implementation Plan, which will be recognized and supported. The watershed team chose the route of selecting priority management areas and phasing them in over the life of the project as a result of funding constraints, a large project area, feasibility of work load, and cost effectiveness. Following the completion of goals and successful implementation efforts in the priority management areas, additional funding will be pursued to complete similar activities throughout the Blue Earth River Watershed. The estimated cost for coordinated implementation over the next 3 to 6 years for implementation funded through the Clean Water Partnership Program include a $450,000 grant for agricultural BMPs, technical assistance, monitoring/evaluation, GIS/Data management, education, and administration/coordination; and a $300,000 loan for ISTS and feedlot upgrades.

Implementation practices applied in the Blue Earth Watershed will contribute to water quality improvement on three scales: the Blue Earth River Watershed, the Greater Blue Earth River Watershed and the Minnesota River. These three scales represent a continuum of perspective from bottom up (watershed view) to top down (basin view). Partnerships involving local, state, and federal participants will result in compatibility of goals and strategies for the three scales.

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